East Glendalough School Declan Cathcart & Russell Harris Form 3 The Human Reproductive System Sexual reproduction involves the fusion of male and female gametes. Gametes are also known as sex cells The male gamete is the sperm cell. The female gamete is the egg. Part Function Testis Makes Sperm Sperm Duct Transports sperm from testis to penis Transports sperm into the female Keeps testes below body temperature so that sperm can be made Penis Scrotum The Male Reproductive System The Female Reproductive System Part Function Ovary An egg is released from here monthly Fallopian tube Site of fertilisation Uterus (womb) Where the embryo/foetus develops Cervix The “neck” of the womb Vagina Sperm is released here during intercourse. The baby exits through here during birth. 1 The Menstrual Cycle The menstrual cycle is a series of changes that take place in the female body approximately every 28 days. The menstrual cycle stops when the woman is pregnant Menstruation is the shedding of the lining of the womb. The menstrual cycle begins with menstruation. The menopause is the age at which a woman stops forming eggs. Day 1 to 5 An egg forms in the ovary. The lining of the uterus breaks down. It is then passed out of the body. The shedding of the lining of the womb is called menstruation. Days 6 to 13 The lining of the womb builds up again. It becomes filled with blood in preparation for the arrival of embryo. Day 14 Ovulation is the release of an egg from the ovary Day 15 to 28 The lining of the uterus has been fully built up. If no fertilisation occurs, then the egg arrives in the womb and dies by day 16. At the end of day 28 the lining of the womb is expelled from the womb. The cycle starts again. The Fertile Period The fertile period is the time during the menstrual cycle during which it is most likely to become pregnant. The egg can survive for 2 days after ovulation The sperm can survive for at least 3 days after intercourse This means there are at least 5 days during which it is most likely But it could happen outside this window outside this period Sexual Intercourse This occurs when the penis is placed inside the vagina. During ejaculation, sperm cells are propelled from the penis as part of a liquid called semen. 2 Semen is a mixture of sperm cells and seminal fluid. The sperm swim through the cervix, into the uterus and up the fallopian tubes. Fertilisation This can occur when male and female gametes (i.e. sperm and egg) meet in the Fallopian tube Fertilisation is the joining of sperm and egg to form a zygote The fusion of sex cells forms a new cell which splits into 2 cells, then 4 , 8 and so on. This group of cells is called an embryo. Implantation The newly formed embryo travels down the Fallopian tube to the uterus It then attaches itself to the lining of the uterus (womb). This is implantation. Pregnancy starts at the moment of implantation. Implantation is the attaching of the embryo to the lining of the womb. Embryo Development The embryo develops in the mother’s uterus. The umbilical cord carries food and oxygen to the baby from the mother and carries waste from the baby to the mother. The placenta is an organ that connects the umbilical cord of the embryo to the uterus, and is where the exchange of nutrients and waste occurs. Pregnancy Pregnancy is the time the baby spends developing in the uterus. Pregnancy lasts from implantation to birth, i.e. 40 weeks During pregnancy the menstrual cycle stops. 3 Part Function Amnion Sac containing amniotic fluid Amniotic fluid Protects the embryo Placenta Allows the passing of food and oxygen from the mother to the embryo Umbilical cord Also allows the waste to pass from the developing embryo to the mother Carries the blood between the embryo and the placenta Labour and Birth Muscular contractions in the uterus begin. This is known as labour. The amnion bursts and the amniotic fluid is released (as in “my waters broke!”). Usually the baby is born head first through the vagina. The umbilical cord is clamped and cut. The placenta passes out shortly after (the “afterbirth”). Puberty is the time during human development when hormones cause changes in the body. In boys, the voice gets deeper, body hair grows around sex organs, and testes start to produce sperm. In girls, hips widen, breasts develop, hair grows around sex organs and the ovaries begin to produce eggs monthly. The menstrual cycle begins. Contraception is the means by which pregnancy is prevented. Natural: not having intercourse during the fertile period. Artificial methods: Condom: rubber sheath covering the penis, prevents the sperm reaching the egg. Contraceptive pill: contains hormones which prevent ovulation. 4 Extra Stuff: 5 Genetics Genetics is the study of inherited characteristics. Inherited characteristics • are passed on from parents to their children • e.g. eye colour, skin colour, blood group, ear lobe shape etc. • are controlled by genes Non-inherited characteristics • acquired or learned • e.g. riding a bike, being able to speak a language, accent etc. • not controlled by genes Chromosomes Chromosomes are long strands or threads of DNA wrapped up with protein. Each nucleus contains lots of thin threads called chromosomes. Chromosomes carry information which controls how your body works and what you look like. Most cells in the human body contain 46 chromosomes. Human sex cells (gametes) contain 23 chromosomes. At fertilisation, the zygote receives one set of chromosomes from each gamete. In this way the zygote contains 23 pairs of chromosomes DNA Each chromosome is made up of threads made of a chemical called DNA The DNA is tied together with some protein. DNA molecules are very very long, which is why they need to be wrapped up in packages (chromosomes) so that they fit in the nucleus Genes Some sections of the long DNA strands are called genes. Each gene gives instructions for a different characteristic. A gene is a section of DNA which contains the instructions for making a protein. Proteins give cells (and organisms) their characteristics like eye colour, skin colour, etc. 6 Extra Stuff: 7 Microbiology Micro-organisms are very small living things. Most can only be seen by a microscope. There are 3 main types of micro-organisms: • Bacteria • Fungi • Viruses. Bacteria Bacteria can only be seen by a microscope, They are single cell organisms, and are smaller than human cells. Most bacteria live off dead material. These bacteria are important as decomposers returning nutrients to the soil. Some bacteria are parasites. This means that they live off living organisms e.g. throat infection, tooth decay, food poisoning. Bacterial diseases can be treated with antibiotics. Effects of Bacteria Useful Harmful Decay dead plants and animals Cause some diseases. Used in food industry to make yoghurt, cheese, butter. Spoil foods – cause milk to go sour. Used in Biotechnology to make insulin, antibiotics. Destroy crops in fields. 8 Fungi Some fungi cause food spoilage e.g. bread mold Potato blight is a plant disease caused by a fungus. Athletes foot is a human disease caused by a fungus. Many decomposers are fungi, feeding on dead plant and animal material, and returning nutrients to the soil. Viruses: Viruses are smaller than bacteria, and are too small to be seen with a light microscope. All viruses are parasites – they must live in or on another organism to survive. Viruses cause the common cold, flu, measles, mumps, chickenpox, AIDS. Our bodies’ white blood cells produce antibodies (not antibiotics) which destroy viruses. Vaccines help the body to create antibodies to particular diseases e.g. the MMR vaccinates children against measles, mumps and rubella. Biotechnology Biotechnology is the use of micro-organisms to make useful substances. Fungi and bacteria can be used to make food, drugs, alcohols, hormones and enzymes. Food manufacture: Bread, beer, yoghurt, salami, olives. Medicines: antibiotics, insulin, human growth hormone, vaccines. Genetic engineering means that organisms can now be altered to produce all kinds of different products. 9 To investigate the presence of micro-organisms in air and soil Agar and Petri Dishes: Sterile petri dishes contain no micro-organisms unless opened. The sterile agar inside the dishes contains food for microorganisms to grow on. Method 1. 4 sterile petri dishes containing agar are labelled A, B, C, and D. 2. A is opened fully to the air for 5 minutes and the lid is replaced B is left closed as a control. C is opened just enough to place a sprinkling of fresh soil. D is opened just enough to place a sprinkling of heat-sterilized soil (a soil control). 3. With all lids closed and taped to the bases, the plates are placed in an incubator at 2030°C for one week. Results A: individual colonies of bacteria and mould growing. B: no micro-organisms present (unchanged) C: lots of different furry moulds and bacterial colonies around the soil and spread across the agar. D: not micro-organisms present (unchanged) Conclusion: air and soil both contain micro-organisms Safety Procedure: Petri-dishes are not opened after incubation, since the microorganisms are unknown and may be harmful. 10 Extra Stuff: 11 The Atmosphere (Part 1) Air is a mixture of gases: (including Argon (1%), Carbon dioxide (0.03%), < 1% water vapour) Experiment: To show that approximately one fifth of the air is oxygen There are three versions of this experiment: Version 1: • • • Push the air backwards and forwards over the hot copper. The oxygen in the air reacts with the copper and is removed from the air. Record how much air remains and so work out the percentage of oxygen at the start. Example: Amount of air at the start = 100 cm3 Amount of air at the end = 80 cm3 Amount of oxygen removed = 20 cm3 % of oxygen in air = 20 % (one fifth) Version 2: • • • Leave for about a week The oxygen in the air reacts with the steel wool (forming rust) and is removed from the air. Record how much air remains and so work out the percentage of oxygen at the start. Example: Amount of air at the start = 100 cm3 Amount of air at the end = 80 cm3 Amount of oxygen removed = 20 cm3 % of oxygen in air = 20 % (one fifth) (100 cm3) Graduated cylinder 12 Version 3: • • As the candle burns it removes the oxygen from the air Record how much air remains and so work out the percentage of oxygen at the start. Example: Amount of air at the start = 100 cm3 Amount of air at the end = 80 cm3 Amount of oxygen removed = 20 cm3 % of oxygen in air = 20 % (one fifth) Properties of Oxygen: • • • Odourless (no smell) Colourless (invisible) Supports combustion (you can burn things in it) Uses of Oxygen: • • • Respiration Burning Welding Experiment: To prepare Oxygen gas Beehive shelf 13 Word equation for the preparation of oxygen: Written above the arrow means “in the presence of…” Manganese dioxide Hydrogen peroxide Water + Oxygen Chemical equation for the preparation of oxygen: MnO2 2H2O2 2H20 + O2 In this reaction, the Manganese dioxide is a catalyst. A Catalyst is a chemical which speeds up a chemical reaction without being used up itself. The test for oxygen gas: It relights a glowing splint Burning in air and in oxygen Because air is only 20% oxygen, burning in pure oxygen gives much faster and brighter reactions than burning in air. Deflagrating spoon Burning carbon in air (burns slowly) Then test the product (Carbon Dioxide) with damp red and blue litmus paper Burning carbon in pure oxygen (burns faster and brighter) Then test the product (Magnesium Oxide) with damp red and blue litmus paper Burning magnesium in air (burns brightly) The blue litmus turns red, showing that Carbon Dioxide is acidic. The red litmus turns blue, showing that Magnesium Oxide Burning Magnesium in oxygen (burns even brighter!) 14 Extra Stuff: 15 The Atmosphere (Part 2) Experiment: To Prepare Carbon Dioxide Note: because carbon dioxide is denser than air, it will remain in the gas jar and not float away. This is why it does not need to be collected over water as oxygen did. Marble chips Word equation: Hydrochloric acid + Calcium Carbonate Calcium Chloride + Water + Carbon Dioxide Chemical equation: 2HCl + CaCO3 CaCl2 + H2O + CO2 Properties of carbon dioxide: 1. 2. 3. 4. It is odourless. It is colourless. It does not support combustion. It is acidic when dissolved in water. 16 Uses of carbon dioxide: Fire extinguishers Fizzy Drinks Dry ice smoke Photosynthesis Fun to be had with Carbon Dioxide: 1) To test for carbon dioxide: Add some lime water and shake. The lime water turns milky. The test for carbon dioxide: It turns limewater milky Word equation: Lime water Calcium Hydroxide + Carbon Dioxide Calcium Carbonate + Water Chemical equation: Ca(OH)2 + CO2 2. CaCO3 + H20 To Show that carbon dioxide does not support combustion: Test tube of CO2 Splint goes out 17 3. To show that carbon dioxide is denser than air Gas jar of CO2 CO2 falls downwards onto the candle 4. To show that CO2 is acidic when dissolved in water Gas jar of CO2 Damp, blue litmus paper - Turns red Experiment: To show that both Water vapour and Carbon Dioxide are present in air: (turns pink) (turns milky) 18 Extra Stuff: 19 Metals Examples of metals: 29 30 13 26 47 79 Cu Zn Al Fe Ag Au Copper Zinc Aluminium Iron Silver Gold 64 65 27 56 108 197 Properties of metals: Metals are… ...usually solids at room temperature ...good conductors of heat ...good conductors of electricity ...Lustrous (shiny) ...Malleable (can be hammered into shapes) ...Ductile (can be stretched into wires) 20 Alloys An Alloy is a mixture of two or more metals. The properties of the alloy are often different from those of the metals which make it. For example brass is an alloy of copper and zinc, and is used to make musical instruments. Brass is harder and stays shinier than either copper or zinc. Examples of alloys: Brass (made of copper and zinc) Bronze (made of copper and tin) Steel (made of iron and carbon) Solder (made of lead and tin) Reaction of Zinc with Hydrochloric acid: Word equation: Hydrochloric acid + Zinc Zinc Chloride + Hydrogen gas Chemical equation: 2HCl + Zn ZnCl2 + H2 The test for Hydrogen gas: makes a lit splint go POP! Zinc Hydrochloric acid 21 Relative reactivities of four metals: The following four metals can be placed in order of their reactivities (i.e from the most reactive to the least) by testing how they react with water and acid. Reactions with water: Only Calcium reacts with water Reactions with acid: Calcium reacts vigorously with dilute acid. Next most reactive is Magnesium, then Zinc. Copper does not react at all. Order of reactivity (from most to least): Calcium, Magnesium, Zinc, Copper 22 Rusting Rusting is a chemical process which turns iron into a new substance (Iron oxide) Rusting can be prevented by... Painting Oiling Galvanising (coating with Zinc) EXPERIMENT: To show that both oxygen and water are needed for rusting: Set up as follows and leave for one week: A: Has water and oxygen B: Has oxygen only (Calcium chloride removes any water from the air) C: Has water only (Uses boiled, cooled water (which has no dissolved oxygen) and a layer of oil on top to prevent oxygen dissolving in the water) Only the nail in tube A rusts, showing that both oxygen and water are needed for rusting. 23 Extra Stuff: 24 Current Electricity An electric current is a flow of charge. To flow it needs a complete loop called an electric circuit. An electric circuit is a complete loop around which a current can flow. Circuit Symbols: Name Photograph Circuit symbol Power supply (Positive connection usually red, negative black) Batteries Positive end Negative end Open (off) Switch or Closed (on) Bulb (in holder) Buzzer or Connecting lead (with connectors on the ends) 25 A simple circuit: Switch open, no current can flow, Switch closed, Current can flow, MANDATORY EXPERIMENT: To test electrical conduction in a variety of materials, and classify each material as a conductor or insulator. Set up as shown. Place different materials across the gap and see if the bulb lights. Place materials across this gap Item What it’s made from Coins Various metals Pen Plastic Does the bulb light? Conductor or insulator? 26 Measuring Current and Voltage Electric current, I, is the amount of charge passing per second and is measured in a unit called the ampere (shortened to amp, and with the unit symbol A). It is measured using an ammeter (note there is no “p” in the word). A photograph and circuit symbol for it is are as follows: Ammeter Voltage, V, is measured in volts, with the unit symbol V. It is measured using a voltmeter. The full definition of it is complicated, but you can think of it as the energy which is available to push a particular charge around the circuit. A voltmeter and its circuit symbol are shown below: Voltmeter Although ammeters and voltmeters look the same, they must be connected into a circuit in different ways. Current must flow through an ammeter, but a voltmeter measures a difference between two points. Here is a sample circuit with both included: Ammeters and voltmeters are often replaced by a digital device which can measure either of them, called a multimeter. It can also measure Resistance (see below) A multimeter Resistance is the ability of a body to resist a flow of charge through it. Conductors have very low resistances, while insulators have very high resistances. Other substances, like those which make up you, are somewhere in between. A resistor is an electrical component which is used in electronics. Resistors Circuit symbol Variable resistor 27 Resistance (R) is measured in ohms, with the unit symbol Ω (“omega”). Ohm’s law: Voltage is proportional to current. Voltage = Resistance x Current, or V = R x I (at constant temperature) 12 V Example 1: Calculate the current flowing in the following circuit: Solution: Voltage, V = 12 V Resistance, R = 6 Ω Current, I = ? Ohm’s law: I V=IxR 12 = I x 6 I= 12 6 = 2A 6Ω Example 2: Calculate the Voltage of the battery in the following circuit: V Solution: Voltage, V = ? Resistance, R = 2 Ω Current, I = 3 A Ohm’s law: I=3A V=IxR V=3x2 = 6V 2Ω Example 3: Calculate the resistance of the resistor in the following circuit: Power supply set at 30 V Solution: Voltage, V = 30 V Resistance, R = ? Current, I = 3 A + - I=3A Ohm’s law: V=IxR 30 = 3 x R R = 30 3 = 10 Ω R 28 MANDATORY EXPERIMENT: To set up a simple circuit, use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them. Set up as in diagram. Adjust the voltage from 1 to 5 volts By adjusting the variable resistor. Record the voltage and current each time. Power supply or battery + Voltage (V) 0 Current (A) 0 1.0 2.0 3.0 4.0 each - 5.0 Variable Resistor Current (amps) Draw a graph of Current against Voltage. It should look like this: Ammeter Resistor Voltmeter Because the graph gives a straight line through the origin (0,0), we can say that the voltage and current are proportional Using a point near the top of the graph: Resistance of the resistor = voltage current = Voltage (volts) = Ω 29 Extra Stuff: 30 SECTION A: 1. An electric current is ………………………………………………………………………………. 2. An electric circuit is ……………………………………………………………………………….. 3. The letter used for electric current is ………………. . The unit used to measure electric current is the …………………………………………….. and this unit has the letter …….. 4. The letter used for voltage is ………………. . The unit used to measure voltage is the …………………………………………….. and this unit has the letter …….. 5. The letter used for resistance is ………………. . The unit used to measure resistance is the …………………………………………….. and this unit has the symbol …….. 6. Resistance is …………………………………………………………………………………….. ……………………………………………………………………………………………………… 7. Ohm’s law states that ……………………………………………. is proportional to ……………………………………….. . This means that if you plot a graph of one against the other you should get …………………………………………………………………… …………………………………………………………………………………………………. 8. Ohm’s law also states that ……………………….. = …………………...x …………………… (at constant temperature) 9. Circle the conductors in the following list: Copper wire plastic ruler air metal door handle glass window 10. Tick the circuits in which the bulb will light (without closing the switches which are open) A D B E C F 31 11. Identify the following circuit symbols: Circuit symbol Name A B C D E F G H I J K 32 12. Calculate the voltage of each of the following batteries or power supplies: V I=3A 3Ω V + - I = 0.5 A 100 Ω 13. Calculate the currents flowing in the following circuits: V = 1.5 V I 3Ω V = 12 V + - I 6Ω 33 14. Calculate the resistances of the resistors in the following circuits: V=6V I=3A R V = 12 V + - I=2A R 15. The following diagram shows part of a circuit which can be used to verify Ohm’s law. There are two things missing from the circuit diagram. Fill in the missing apparatus. Label all parts of the circuit. Variable power supply + - 34 16. The following circuit diagram contains a voltmeter and an ammeter, but their symbols have been left out. Which is which? Draw and name the other three components in the circuit. X Y 17. Calculate the voltage of the battery V I=6A 2Ω V=6V 18. Calculate the current flowing in the following circuit: I 3Ω 35 V=9V 19. Calculate the resistance of the resistor in the following circuit: I=2A R 13. State Ohm’s law. In an experiment to verify ohm’s law, the following results were obtained: Use the data to plot a graph (on graph paper) of voltage against current. Explain why the graph verifies Ohm’s law. Use the graph to calculate the resistance of the resistor in the circuit. Voltage (V) 0 1.0 2.0 3.0 4.0 5.0 6.0 Current (A) 0 0.25 0.50 0.75 1.00 1.25 1.50 36 Uses of Electricity Series and Parallel circuits: Bulbs wired in series Bulbs wired in parallel In Series: • • When bulbs are wired in series they are dimmer because they share the voltage of the battery. When one is removed the other goes out as the circuit has been broken. In Parallel: • • When bulbs are wired in parallel they do not lose brightness because each is still receives the full voltage. When one is removed, the other one stays lit as it is still connected at both ends to the battery and so the circuit is not broken. The lights in your house are wired in parallel, and not in series. If they were in series, every time one bulb blew, all of the lights would go out. Older sets of Christmas tree lights were wired in series. You may still have some at home. When one bulb blows they all go out because the circuit is broken, and you have to replace each one in turn to find out which one it is. Headlights in a car are wired in parallel. This means that if the bulb on one side blows, the other one will stay on. The three Effects of electric current 1. The heating effect. An electric current can cause a substance to heat up. 37 INVESTIGATION: To demonstrate the heating effect of an electric current Electricity flowing in the coil causes it to heat up. This heats the water and the effect can be seen by a rise in temperature of the water. Battery or power supply thermometer water Heating coil Examples of the heating effect: 1. 2. 3. An electric kettle. Light bulb. The filament of a light bulb heats up so much when an electric current passes through it, that it glows white-hot, giving out light. A fuse. This is a safety device which is found in plugs (see later) and on fuse boards (where the electricity enters your house). It contains a thin piece of wire, through which the current has to flow. If the current goes above a particular value (as it would, for example, if you were being electrocuted), the wire heats up enough to melt, breaking the circuit and cutting off the current. 13 amp fuse from a plug Glass fuse showing the thin wire inside that melts Circuit symbol for a fuse Different fuses have different ratings (3 amp, 5 amp, 13 amp, 25 amp, etc). For example, a 5 amp fuse will “blow” when the current going through it goes above 5 amps. If, for example, If a hair dryer uses 4 amps, then the best fuse to use in the plug would be a 5 amp one (the next one up). 38 The Chemical effect an electric current can cause a chemical reaction. Examples of the chemical effect: 1. Charging a rechargeable battery. 2. Electroplating. 3. Electrolysis of water. (See the sheet on water) The Magnetic effect. An electric current creates a magnetic field around it. INVESTIGATION: To demonstrate the magnetic effect of an electric current. When a current flows in the wire, a magnetic field is created which can cause the compass needle to turn 39 Examples of the magnetic effect: 1. 2. 3. An Electromagnet. An electric motor. Circuit breakers. These have replaced fuses in modern fuse boards. A circuit breaker uses an electromagnet to flip a switch to “off” when the current reaches that same value. The main advantage is that they can be reset by flipping the switch back when the fault is fixed, instead of having to go out and buy a new fuse. Direct current and alternating current (d.c. and a.c.) The electric current which flows from a battery is known as direct current (d.c.). It travels around the circuit in one direction - out one end of the battery and in the other. However there is another type of current called alternating current (a.c.). Instead of travelling in one direction, it keeps changing direction. Batteries do not supply this type of current. A.c. comes from the mains (the plugs on your wall) and from a.c. power supplies. Direct current (d.c.) flows in one direction only. Alternating current (a.c.) keeps changing direction. Circular saw - moves in one direction (like d.c.) Hand saw - moves back and forth (like a.c.) + Battery (supplies d.c.) - d.c. power supply a.c. power supply 40 Mains supply • • It is alternating current (a.c.) It has a voltage of about 230 volts. Earth wire (green and yellow) - for safety Fuse Live wire (brown) Neutral wire (blue) The wiring in a plug The kilowatt-hour Each home has an electricity meter which measures how much electricity you have used, so the ESB can send you a bill. They use a unit of energy called the kilowatt-hour (kWh) which makes it easy to calculate how much each appliance uses. Each kilowatthour costs about 15 cent Electricity meter—measures the number of kW-h used Number of kilowatt-hours used = Power (in kilowatts) x time (in hours) Remember that 1 kilowatt (kW) = 1000 watts (W) You may find it easier to remember this as: Kilowatts-hours = kilowatts x hours Cost per kWh Number of kWh used Previous meter reading Present meter reading 41 In both of the following examples, take the cost of 1 kWh to be 15 cent Example 1: What is the cost of running a 3000 W tumble dryer for 2 hours? Solution: Power (in kW) = 3 kW Time (in hours) = 2 hours Number of kilowatt-hours used = Power (in kilowatts) x time (in hours) = 3 kW x 2 hours = 6 kWh If each kWh costs 15 cent, then: Total cost = 6 x 15 cent = 90 cent. Example 2: What is the cost of running a 100 W light bulb for 4 hours a day for a week? Solution: Power (in kW) = 0.1 kW Time (in hours) = 4 hours x 7 days = 28 hours Number of kilowatt-hours used = Power (in kilowatts) x time (in hours) = 0.1 kW x 28 hours = 2.8 kWh If each kWh costs 15 cent, then: Total cost = 2.8 x 15 cent = 42 cent. Example 3: What is the cost of running a 2.0 kW kettle for 15 minutes? Solution: Power (in kW) = 2.0 kW Time (in hours) = 0.25 hours (one quarter of an hour) Number of kilowatt-hours used = Power (in kilowatts) x time (in hours) = 2.0 kW x 0.25 hours = 0.5 kWh If each kWh costs 15 cent, then: Total cost = 0.5 x 15 cent = 7.5 cent. 42 Extra Stuff: 43 SECTION A: 1. Electrical components (e.g. bulbs) are said to be in ………………………………... if they are connected one after the other. 2. Electrical components (e.g. bulbs) are said to be in ………………………………….if they are connected side by side. 3. If bulbs are connected in a circuit in series, when one is removed, the other …………………………………………………………….. 4. If bulbs are connected in parallel in a circuit, when one is removed the other …………………………………………………………….. 5. The three effects of electric current are the …………………………………….. effect, the ……………………………………………. effect and the ……………………………………….. effect. 6. An example of the heating effect would be ……………………………………………………. 7. An example of the chemical effect would be ………………………………………………….. 8. An example of the magnetic effect would be …………………………………………………. 9. The fuse is an example of the …………………………………………….. effect of an electric current. It is there for ………………………………………… reasons. When a current reaches a certain value, it ………………………………………. , cutting off the current. 10. The circuit breaker is an example of the …………………………………………………….. effect of an electric current. It is similar to a fuse, but it doesn’t need to be replaced when it ………………………………….. 11. Direct current (d.c.) flows ……………………………………………………………………….. 12. Alternating current (a.c.) flows ………………………………………………………………….. 13. The mains supply has a voltage of ……………………… volts and is ………………………………………… current. 14. In a plug, the live wire is coloured ………………………………………… , the neutral wire is coloured …………………………………………. and the earth wire is coloured ……………………………………………………… . The live wire is connected through a …………………………………………………. for safety reasons. 15. The unit used by the ESB to measure the amount of electricity used is called the ………………………………………………………. and its symbol is the ………………….. 16. Number of kiloWatt-hours used = ………………………. (in ………………………..) x …………………………………….. (in …………………………………) 17. An example of a low power appliance is a …………………………………………………….. 18. An example of a high power appliance is a ……………………………………………………. only. 44 19. Label the following diagram of a plug: ………………………... ………………………… …………………………... …………………………. 20. How much money would you save by changing from a 100 W normal light bulb to a 15 W energy saving light bulb over a full week’s use (take the cost of each kWh to be 15 cent)? SECTION B: 1. Explain, with diagrams, the difference between series circuits and parallel circuits. Explain why Christmas tree lights might be wired in parallel rather than in series. 2. List the three effects of an electric current. 3. In the case of each of the following, state which of the three effects they use: (i) 3. An electric drill (ii) A battery charger (iii) A loudspeaker (iv) Electroplating (v) A light bulb (vi) An electric oven (vii) A fuse (viii) A circuit breaker. Describe how a fuse works. An electric lawnmower uses 6 A of current when running. Which fuse (3 A, 5 A or 13 A) should be used? Explain your answer. 4. Give two differences between a fuse and a circuit breaker. 5. What do the abbreviations d.c. and a.c. stand for? Explain the difference between d.c. and a.c. 6. List the names and colours of the three wires in a plug. Which wire is dangerous to touch? Which wire is there for safety? Explain how it keeps you safe. 7. The ESB charges for its electricity in “units”. What is the correct name for these units and give an equation which allows you to calculate how many units an appliance has used. 8. Calculate the cost of the following, using the table of power ratings given on page ___ . In each case, take the cost of each kWh to be 15 cent. (i) Listening to a 1 hour long cd. (ii) Watching an episode of your favourite soap (which lasts 30 minutes) (iii) Washing a load of clothes, if it takes 2 hours (iv) Heating water in an immersion heater for three hours a day for two weeks. 45 (v) 9. Cooking a microwave dinner which takes 10 minutes to cook. In an experiment to compare series and parallel circuits, a student connected up two bulbs in series. Draw a circuit diagram of the circuit. The student noticed that the two bulbs lit only dimly. Explain his observation. He then removed one of the bulbs. What did he observe happen to the other bulb? Explain why this happened. The student then connected up the two bulbs in parallel. Draw a circuit diagram of the circuit. He noticed that the two bulbs were now lighting brightly. Explain why this was so. He then removed one of the bulbs. What happened to the other bulb? Explain this observation. 46 Electronics The diode The diode will only allow electric current through it in one direction. It is a bit like a turnstile, which only allows people to pass through it in one direction. The diode Electric current can only flow in this direction 6V 6V Bulb lights Bulb doesn’t light Remember the current comes out of the positive side of the battery (the wide end on the diagram) and into the negative side (the small end). The light-emitting diode (LED) A variation on the diode is the light-emitting diode, or LED. It has the same effect as the diode, except that it also gives out light. They need very little voltage to work (about 1.2 volts) and use very little current. For this reason, they are often used in place of ordinary light bulbs, as they are much more efficient. If used in torches or bicycle lights, the batteries will last much longer than they would have with ordinary bulbs. 47 LEDs. The longer leg should be connected to the positive side of the battery. LED circuit symbol Because it uses a small current, a resistor of about 300 Ω is usually wired in series with an LED, to reduce the current going through it. If you connect one straight up to a 6 V battery it will The Torre Agbar tower in Barcelona is probably glow brightly for a few moments and then stop working. covered in 4500 colour-changing LEDs 300 Ω LED wired in series with a resistor to protect the LED from too much current The following circuit shows an LED in operation. The second one shows how, just like with an ordinary diode, the current can only flow in one direction through it. Notice that these circuits do not require a bulb like the last ones, as the LED lights up itself, showing if a current is flowing. 300 Ω 300 Ω LED lights LED does not light as it is connected the wrong way around. 48 What would happen if you connected up a 6 V a.c. power supply instead of the 6 V d.c. battery? Because the current keeps changing direction with a.c., the LED would only light for half the time, when the current was going through it in a forward direction. So the LED would seem to light dimly. A.c. power supply 300 Ω LED lights dimly Example 1: The following circuit contains a green and a red LED connected in parallel with a battery and switch. A resistor is in series with each LED to protect it from too much current. Green LED 300 Ω 300 Ω Red LED (i) (ii) What would you expect to see happen when the switch is closed? What would you expect to see happen if the battery is turned around in the circuit and then the switch is closed? (iii) What would you expect to see happen if the battery is replaced with an a.c. supply and the switch is closed? Solution: (i) When the switch is closed only the green LED will light as it is the only one which is the correct way around in the circuit for it to light up. (ii) When the battery is reversed only the red LED will light as it is now the only LED which is the correct way around to light. (iii) When an a.c. supply is used instead of the battery the current keeps changing direction so each of the LEDs will flash on and off quickly, and the two LEDs will appear to be dimly lit. 49 The light dependent resistor (LDR) This is a resistor whose resistance changes with the amount of light shining on it. The more light that shines, the lower its resistance. Light dependent resistor LDRs are used as light detectors. They can be used to open automatic doors of to switch on and off street lights. EXPERIMENT: To show the action of an LDR. Method: 1. Set up the circuit as shown. 2. Cover the LDR with your hand and note the brightness of the LED 3. Allow bright light to fall on the LDR and note the brightness of the LED Results: The LED shines brighter when light falls on the LDR. 6V 6V No light shining Bright light shining LED lights dimly LED lights brightly Conclusion: When light falls on the LDR its resistance drops, allowing more current through to light the LED. 50 EXPERIMENT: To measure the resistance of an LDR under varying degrees of brightness of light Ω Procedure: 1. Connect up a circuit with the LDR and the ohmmeter as shown. 2. Switch on the torch. Using the ruler, shine it onto the LDR from a distance of 20 cm. 3. Measure and record the resistance using the Ohmmeter. 4. Move the torch 2 cm closer and record the new resistance. Continue measuring the resistance at 2 cm intervals until the torch is touching the LDR. 5. Plot a graph of resistance (y-axis) against brightness (x-axis) (with the starting position of LDR the torch representing Ohmmeter (or multimeter brightness of 1, and the measuring resistance) next position a brightness of 2, and so on). Results: Brightness 1 2 3 4 5 6 7 8 9 10 11 Resistance (ohms, Ω) Conclusion: The resistance of an LDR was found under different levels of brightness of light. Note: The graph should look something like this: It can be seen that the resistance decreases as the brightness Resistance increases Brightness 51 Extra Stuff: 52 SECTION A: 1. A ……………………………………….. allows electricity to flow through it in one direction only. 2. A diode which also gives out light is a …………………………………………………………. diode. 3. A LED must have a …………………………………. connected in series with it to protect it from receiving too much ………………………………………… 4. An example of a use of an LED is ………………………………………………………………. 5. A resistor whose resistance decreases as the brightness of light shining on it increases is called a …………………………………………………………………… resistor. 6. An ………………………... example of a use of an LDR is ………………………… …………………………... …………………………. ………………………………………………………………. ………………………………………………………………………………………………………. 7. Identify the following electronic components: Circuit symbol Name A B C 53 8. In each of the following diagrams, say what you will observe, and explain why: 6V A What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. 6V B What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. C What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. 300 Ω 54 D What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. 300 Ω E What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. 300 Ω F What you observe: ………………………….. …………………………………………………. Explain: ………………………………………. …………………………………………………. ………………………………………………….. …………………………………………………. Bright light shining 55 SECTION B: 1. What is the function of a diode? Draw the circuit symbol for a diode, showing which end should be connected to the positive end of a battery for a current to flow through it. 2. Give a difference between how a LED should be put into a circuit and a diode. Explain the reason for this difference. Give a use of an LED. 3. State what happens to the resistance of an LDR when a bright light shines on it. Give a use of an LDR. 4. Describe, with the aid of diagrams, an experiment to show the function of diode. 5. Describe, with the aid of diagrams, the operation of an LED, and how to investigate the effect of reversing the LED in the circuit. 6. Describe, with the aid of a diagram, an experiment to measure the resistance of an LDR under varying degrees of brightness of light. 7. Describe, with the aid of diagrams, how to show the effect of an LDR on the current flowing in a circuit. 56 Light Luminous objects are a sources of light. Non-luminous objects are seen as a result of light reflecting from them. Luminous objects Non-Luminous objects Light travels in straight lines - shadows We can hear people talking around a corner, but we can’t see them. This is because, unlike sound, light travels in straight lines. If it didn’t, we wouldn’t be able to see anything clearly. One way we can know this is because of shadows. When you stand with your back to the Sun, a shadow is formed on the ground in front of you because you are blocking out the sunlight from that part of the ground. If light didn’t travel in straight lines, it could bend around you and a shadow wouldn’t be formed. 57 MANDATORY EXPERIMENT: To show that light travels in straight lines and to explain how shadows are formed. Part (a): Method: 1. Set up as shown, lining up the holes in the cards with a stretched piece of string. 2. Move one of the cards a little to one side. Look in again. Cards with holes Results: You can no longer see light from the torch. Conclusion: Light travels in straight lines. That is why the torch cannot be seen unless the holes are in line. Blu-tack Part (b): Method: In a darkened room, shine the torch on the cut-out shape to form a shadow on the screen as shown. Results: A shadow is formed which is the same shape as the cut-out. Conclusion: A shadow was formed because the cut-out blocked the light from shining on the screen. The shape of a shadow is the same as the outline of the object causing it. Normal Reflection is when light bounces off a surface. A A B B C C Light is always reflected back at the same angle it strikes a mirror 58 Image in a plane mirror Notice that the image formed in a plane (flat) mirror is back to front. This is why the word “Ambulance” is written back to front on the front of an ambulance—so that it’s the right way round when seen in a driving mirror. Image of the candle 450 The Periscope Periscope is made with two mirrors arranged as shown. This allows you to see over tall objects. 450 59 MANDATORY EXPERIMENT: To (a) investigate the reflection of light by plane mirrors, and illustrate this using ray diagrams; (b) demonstrate and explain the operation of a simple periscope. Part (a): Method: 1. Set up as in diagram 2. Mark the path of the beam on the paper. 3. Draw the beam on the page and measure angles A and B. 4. Repeat with different angles of the beam. paper light box slit x x B Results: Angle A and B are equal each time. x x m irr or Conclusion: Light is always reflected from a mirror at the same angle at which it strikes it. Part (b): Method: 1. Set up two mirrors as shown in clamp stands. mirror A normal clamp Results: You can see over the book. book Conclusion: You have constructed a periscope. You can see over the book because light is reflected from the top mirror to the bottom mirror and into your eye. 450 clamp stand 60 Uses of reflection Refraction Refraction is the bending of light as it passes from one medium to another. normal For example, here is the path taken by light as it passes from air to water: air A glass B A air B water glass B A air ...and this is the path through a glass block: Refraction can make a pencil look bent in a glass, or make a fish appear nearer the surface than it really is: B A 61 EXPERIMENT: To show the refraction of light as it passes from (a) air to glass, (b) glass to air, (c) air to water, and (d) water to air. Parts (a) and (b): Method: Shine a beam of light from a light box through a glass block as shown. light box x x paper Glass block or box full of water x Parts (c) and (d): Method: Replace the glass block with a transparent plastic box full of water and shine the beam through as before. air x Results: The beam bends towards the normal when travelling from air to glass and from air to water. The beam bends away from the normal when travelling from glass to air and from water to air. Conclusion: Light is refracted as it passes from one medium to another. It bends towards the normal when travelling into a denser medium and away from the normal when travelling into a less dense medium. Lenses We have seen that when light passes right through a piece of glass it ends up travelling in the same direction as it went in. This is only true if the two sides of the glass are parallel. If they are curved then we have a lens. There are two main types, convex and concave. Convex lens - bends light inwards Concave lens - bends light outwards. Notice that the beams through the centres are not bent at all. A convex lens can be used as a magnifying glass. It can be used to get an enlarged view of something you are looking at (see left). A concave lens has the opposite effect. It makes things seem smaller (see right). 62 EXPERIMENT: (a) To show refraction of light as it passes through a lens, (b) to demonstrate the operation of a magnifying glass. Apparatus: Convex lens, light box with triple slits and power supply, paper. paper light box Part (a): Method: 1. Shine light from the three slits of the light box onto the lens as shown, so that the paths of the beams can be seen on the paper. slits convex lens Results: The beams can be seen to be bent inwards by the lens. Conclusion: A convex lens can bend light inwards. Part (b): Method: 1. Hold the convex lens a few centimetres above an open book. Results: The text on the page is magnified. Conclusion: A convex lens can be used as a magnifying glass and can make things seem bigger. Blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah Uses of refraction: Colour The colours in white light can be split up so we can see them using a triangular piece of glass called a prism. This is called dispersion. Dispersion is the splitting of light into the colours it is made of. This band of colours is called a spectrum of light, and it contains the colours of the rainbow. 63 They are: Red, Orange, Yellow, Green, Blue, Indigo and Violet. EXPERIMENT: To produce a spectrum of white light. Apparatus: Light box with single slit and power supply, glass prism, sheet of paper. light box Method: 1. Shine a beam of white light from the box through a prism as shown, so that the light shines on the paper on the other side. 2. Note the colours which are formed and their order. prism slit Results: The colours of the rainbow are seen on the paper. Red light is bent the least, violet the most. Conclusion: A spectrum of white light was produced. table The speed of light Light travels much faster than sound. This can be observed during a lightning storm. You see the flash of lightning almost instantly, but it can take several seconds for the thunder to arrive. If you see someone in the distance hitting a golf ball, there is a noticeable difference between when you see the club hit the ball and when you hear the strike. 64 Extra Stuff: 65 Chapter 8 - Light 1. Luminous objects are …………………………………………………………………………… Non-luminous objects are ………………………………………………………………………. ……………………………………………………………………………………………………… 2. Light is a form of …………………………………………………… This can be demonstrated using a ……………………………………………………………………………………………. 3. Shadows are formed because light travels in …………………………………………………. 4. Reflection is when ……………………….………………………………………………………… ……………………………………………………………………………………………………….. 5. When light strikes a mirror, it is reflected back at ……………………………………………… 6. The arrangement of two mirrors in such way so that you can see over things is called a …………………………………………………………….. 7. An image formed by a plane mirror is formed …………………………………….. the mirror. 8. Three applications of reflection are …………………………………………………………….., ………………………………………….. and ……………………………………………………. 9. Refraction is ……………………………………………………………………………………….. ……………………………………………………………………………………………………….. 10. When light passes into a more dense medium it is bent ……………………………………… the normal. When it passes into a less dense medium it is bent …………………………….. the normal. 11. Refraction can make a swimming pool look ………………………..……….. than it really is. 12. A convex lens bends light ………………………………………………………. A concave lens bends light ……………………………………………………… 13. A magnifying glass can make things look …………………………………………… It is made with a ……………………………………………… lens. 14. Three applications of refraction are ……………………………………………………………., …………………………………………… and ……………………………………………………. 15. The colours of the rainbow are ………………………………………………………………… ………………………………………………………………………………………………………. 16. If you mix all the colours of the rainbow you get …………….…………………………. light. 17. Dispersion is ………………………………………………………………………………………. ……………………………………………………………………………………………………….. 18. White light can be dispersed to form a ………………………… using a …………..……….. The …………………………….. light is bent the least, and the …………………………….. light is bent the most. 19. The speed of light is …………………………………………………metres per second. 66 20. Light travels ……………………………………………… than sound. 21. Complete the following diagram showing light striking a mirror: 22. The below diagram shows a periscope. Complete the path of the light ray passing through it: 23. 23. The following diagram shows the path of two light rays coming from a ball and striking a plane mirror. Complete the paths of the rays. Use these rays to show where the image is formed: 67 24. The following diagram shows a ray of light striking a glass block. Complete the path that the ray might take through the block and out the other side: 25. Copy and complete the following diagram showing the paths of light rays entering water from air and exiting from water to air: air water 26. Copy and complete the following diagrams showing the paths of light rays through a convex and a concave lens: 68 27. Copy and complete the following diagram showing white light passing through a prism. Write the names of the colours formed down the right hand side of the screen: screen 28. Place the following items into the appropriate column of the table (some are tricky!): The Sun, the Moon, a teddy bear, a light bulb, a photograph hanging on a wall, a photograph seen on a computer screen, a film seen on television, a film seen at the cinema. Now add two items of your own to each list. Luminous Non-luminous 69 SECTION B: 1. What is the difference between luminous and non-luminous objects? 2. Describe the difference in the way ordinary objects reflect light and the way a mirror does. 3. Define the following terms: Reflection, Refraction, Dispersion. 4. It would take a beam of light 0.02 seconds to travel from Cork to Moscow. If the speed of light is 300,000,000 m/s, how far is it between the two cities (you will need to use the velocity equation on page ___ )? Can you give your answer in kilometres? 5. Draw a diagram showing light passing through a periscope. Explain why the final image is not back-to-front, even though it uses mirrors. 6. Describe an experiment to show that light is a form of energy. What are the energy changes taking place? 7. Draw a diagram of apparatus arranged to show that light travels in straight lines. How can you tell that the holes are lined up? 8. Draw a diagram of apparatus arranged to show how shadows are formed. 9. Draw a diagram of apparatus arranged to show light being reflected from a plane mirror. What does this tell us about the angle the light is reflected at? 10. Draw a diagram of apparatus arranged to show the refraction of light as it passes through a glass block. How is the path of the beam found? How could this be done with water instead of glass? 11. You are given two convex lenses of different strengths. Describe, with diagrams, an experiment to find out which lens bend light the most. 12. Draw a diagram of apparatus arranged to find out which colour, red or blue, is bent the most when white light passes through a prism. 13. You are standing with your back to the Sun and a shadow is cast in front of you. Explain why the shadow is formed. 14. Solar panels are placed on the roofs of houses and are used to generate electricity. What does this tell you about light? 15. Match the following properties of light to the following things you see around you (some may involve more than one): A. Refraction (i) B. Dispersion C. Reflection When using a hose in the garden, different colours can sometimes be seen in the spray. (ii) A “hall of mirrors” at a fairground can make you look smaller or taller. (iii) A camera can use a zoom lens to make things seem closer. (iv) Glasses can make the wearer’s eyes look smaller or bigger. (v) A torch lets you see in the dark. 70 16. One of the following two pictures is reflected in a mirror. The other is the view seen through a periscope. Which is which? Explain how you can tell. 71 Sound EXPERIMENT: To show that sound is a form of energy. Radio Tiny polystyrene ball on a thread Ball vibrates The sound makes the ball move, and so the sound is doing work. This proves that sound is a form of energy. EXPERIMENT: To show that sound is produced by vibrations Tiny pieces of polystyrene sitting in the speaker Speaker connected to a sound source (e.g. a radio) The polystyrene jumps up and down, bumped by the cone The speaker is producing sound by vibrating the cone up and down. This shows that sound is produced by vibrations. Transmission of sound “Transmission of sound” means the way in which it travels from one place to another. Sound can travel through solids, liquids and gases. The substance it is travelling through is called the medium. Unlike light, sound cannot travel through a vacuum. It needs a medium. This is why we can see the Sun, but not hear it - the sound cannot travel through the vacuum of space. The Sun - Bright but not loud. 72 EXPERIMENT: To show that sound needs a medium to travel through. Results: As the air is pumped out the sound from the bell gets softer until it can no longer be heard. When the air is allowed back in again, it can be heard once more. Conclusion: The sound cannot travel through the vacuum inside the jar. Sound needs a medium to travel through. to power supply bell jar bell To vacuum pump Sound detection in the ear When sound enters the ear it causes your ear drum to vibrate. This vibration is converted into a signal which is sent to your brain. Loudness The ear can also respond to different loudness of sounds. A louder sound means that the vibrations are more vigorous. We refer to the loudness of a sound as its sound level. The scale on which sound levels are measured is the decibel scale (dB). 0 dB is the softest sound we can hear. Here are some examples (which you don’t need to learn): 0 dB 20 dB 40 dB 60 dB 80 dB 100 dB 120 dB 130 dB 140 dB 160 dB - The softest sound the ear can detect. A whisper Quiet conversation Normal conversation City traffic Chain saw Rock Concert Threshold of pain. When it starts to hurt Jet taking off Ear drum bursts 73 People working with noise levels above 90 dB must be given ear protection by law. The following safety sign means that ear protectors must be worn in that area: Sound levels may be measured easily with a sound level meter. Quite often sound is unwanted (like when you are trying to go to sleep). It can be reduced in several ways. Insulation in the walls and double glazing can help to reduce noise levels in our homes. Trees are often planted between busy roads and houses to cut down traffic noise. The speed of sound Sound travels at different speeds in different media. In air it goes at about 340 m/s. In water the speed is about 1500 m/s (over four times faster), and in steel it is about 5000 m/s (about fifteen times faster). The speed of sound is much slower than the speed of light (which is almost a million times faster). This means that you see things in the distance before you hear them. Examples of this are: • You see a car door closing in the distance before you hear the slam. • You see fireworks exploding in the sky before you hear the bangs. • Runners can appear to have a false start in a race as they seem to move before you hear the bang of the starter gun. • The sound of an aeroplane overhead can seem to be coming from behind it because the sound you hear left the plane many seconds before. • You see a lightning flash seconds before you hear the thunder. Reflection of sound HELLO! Echoes are reflected sounds. 74 Extra Stuff: 75 Chapter 9 - Sound 1. Sound is a form of .......................................................................... . This can be shown by the fact that it can do .........................................................., causing something to move. 2. Sound is caused by ....................................................................... . These travel from the source of the sound through the air to your ear. They cause the ......................................... inside to ........................................................ 3. Sound cannot travel through a ......................................................... . It needs a ............................................................ to pass through. This is why we can ..................................... the Sun but not .................................................. it. 4. Sound travels ..................................................... in steel than it does in air. 5. The scale which measures sound levels is called the .......................................................... scale. 6. .............................................................................. should be used to avoid ear damage due to loud sounds. 7. Unwanted noise can be reduced using .............................................................................. 8. ............................................. are reflected sound. 9. Light travels .............................................. than sound. This is why you .................................... a car door slamming in the distance before you ........................................................ it. 10. The movie “Alien” has the tag-line: “In space, no one can hear you scream”. Why is that? ………………………………………………….. ………………………………………………….. ………………………………………………….. 11. In science fiction movies, you often see space ships explode in space with loud bangs. Why is this a mistake? ……………………………… ………………………………………………….. ………………………………………………….. 12. In movie westerns, you sometimes see someone place their head on the ground to hear distant horses. Why does this work? ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. 76 13. If you saw the following sign, what would it mean? ………………………………………………………………… ………………………………………………………………... 14. Why are trees sometimes planted between busy roads and housing estates? ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. 15. Explain why athletics races can sometimes appear to have a false start to spectators in the crowd: ………………………………………………………………………………………….. ………………………………………………………………………………………………………. 16. Explain why, in large cathedrals, it can seem that the people at the back are not singing in time with the people at the front: ………………………………………………………………... ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. 17. Explain why, when waiting for a train, you sometimes hear a metallic jingling long before you see or hear the actual train: ……………………………………………………………….. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. 18. Why do aging rock stars often have bad hearing? ………………………………….. Pardon? ……………………………………………... ……………………………………………... ……………………………………………… 77 SECTION B: 1. When you place your hand on a speaker playing loud music you can feel it vibrate. What two things does this tell you about sound? 2. Describe how sound gets from a beating drum to your ear and how your ear and brain detect it. 3. Why can sound not travel through a vacuum? 4. Place the following media in order of the speed that sound passes through them. Steel 5. Air Water Rock Why do some workers have to wear hearing protection? What would happen if they didn’t? 6. What is measured on the decibel scale? Give two examples of different sounds and their number of decibels. 7. What causes echoes? A student stands some distance away from a cliff and fires a starter pistol. 1 second later an echo of the bang is heard from the cliff. If the speed of sound if 340 m/s, how far away is the cliff (remember that the sound has to travel there and back)? 8. Explain why you see the lightning before you hear thunder. You are lying in a tent listening to a thunderstorm outside. You see a flash of lightning, and 9 seconds later hear the thunder. How far away is the storm (sound travels about 3 km in 1 second)? 9. Give two examples of how echoes are used by animals, and two examples of how they are used by people. 10. Describe, with the aid of a diagram, an experiment to show that sound is a form of energy. 11. Describe, with the aid of a diagram, and experiment to show that sound is caused by vibrations. Can you think of another way of showing this? 12 Describe, with the aid of a diagram, and experiment to show that sound cannot travel through a vacuum. 13. Describe, with the aid of a diagram, and experiment to show the reflection of sound. 78 Latent heat and Boiling Point changing with Pressure. Latent Heat Latent heat is the heat required to change the state of a substance. Imagine that you take an ice cube from the freezer, where it was at a temperature of -20 oC, and heated it, using a thermometer to record the temperature as you went along. The ice melts, and then is heated to its boiling point where it boils and evaporates to steam. Imagine then that you then continued to heat this steam. If we plot a graph of the temperature against the amount of heat added it would look like this: This looks very complicated, but we will explain it in smaller sections: Temperature (oC) F Latent heat 100 D evaporating E Latent heat 0 B melting C Heat added (J) -20 A • • • • • • The ice begins at A at -20 oC. Between A and B its temperature is rising as it is heated. When it gets to B it starts to melt (0 oC), and remains at that temperature until all of it is melted (at C), and it has now become water. Between C and D it is being heated up to its boiling point. At D it starts to boil (100 oC). Again, it stays at this temperature until all of it has evaporated (at E), and it has now become steam. Between E and F the steam is being heated up further, and its temperature is rising again If you put a drop of pure alcohol on your hand, it feels very cold. This is because it evaporates easily and as it does so, it takes the latent heat it needs from your hand, making it feel cold. 79 If, instead of starting with the ice, we had Cooling curve started with the hot steam and cooled it, we Temperature ( C) 100 would get exactly the same graph, except it would be back to front. In this case in is known as a cooling curve. Instead of having to put heat in to melt it and evaporate it, the exact same quantities of heat are given 0 out or removed. This is why a scald from o Heat removed (J) steam at 100 C is worse than a splash of -20 o boiling water at 100 C. The steam condenses on your skin, giving away its latent heat and making it feel hotter. o EXPERIMENT: To plot a cooling curve and explain its shape in terms of latent heat. Note: This cooling curve will only show the latent heat removed during freezing. It would be too difficult and dangerous to measure and change the temperature of a hot gas. Apparatus: Boiling tube, naphthalene (or stearic acid or lauric acid), thermometer, water bath, beaker of cold water Method: 1. place a few cm3 of one of the above solids into a water bath of nearly boiling water until the solid dissolves (this may take 20 minutes). Leave it for a further five minutes to make sure that its temperature is well above the melting point. 2. Place a thermometer into the boiling tube and leave it to cool in a beaker of cold water, measuring the temperature every minute until it has fallen to about 30 oC. This may take another 20 minutes. Record the temperatures and times in a table as shown below. 3. Plot a graph, on graph paper, of temperature against time (you are assuming that the heat loss is constant with time so it doesn’t matter that the graph shows time instead of heat lost on the horizontal axis). Results: Record your results in a table as shown here: Temperature (0C) Time (minutes) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 80 Your graph should have the following shape: Temperature (oC) Time (minutes) Conclusion: The liquid cools until it reachs its melting point, and then turns into a solid. While this is happening, the temperature remains the same while the latent heat is removed. When it all turns into a solid, the temperature begins to fall again. Boiling point and Pressure The boiling points given above are taken at normal atmospheric pressure. If the air pressure increases, the boiling point increases too. This is how pressure cookers work. They boil food in a sealed pot which increases the pressure inside, making the water boil at about 120 oC instead of the normal 100 oC. This allows the food to cook quicker. The opposite happens at low pressures. If you went to the top of mount Everest, water would boil at about 70 oC, so you wouldn’t be able to make a very hot cup of tea. This tea is rubbish. Make your own next time. 81 EXPERIMENT: To investigate the effect of pressure on the boiling point of water. Apparatus: Plastic syringe with a rubber tube attached, clip to seal the tube, water, Bunsen burner, tripod, gauze, beaker (or an electric kettle to provide the boiling water). Method: 1. Boil some water (either in a beaker over a Bunsen burner or in a kettle). 2. Remove the Bunsen or switch off the kettle. The water will stop boiling as its temperature drops to just below boiling point. 3. Draw a few cm3 of water into the syringe through the tube. Be careful not to burn yourself on the hot water or scald yourself on the steam. 4. Seal the tube with the clip 5. Pull out the plunger of the syringe to about half way. This will lower the pressure above the water. 6. Observe what happens to the water. Results: The water starts to boil again. Conclusion: Lowering the pressure above the water lowers its boiling point to below that of the temperature of the water in the syringe and it began to boil again. This shows that lowering the pressure lowers the boiling point. Note: Here are some sample figures to help you understand what happened. Say the water in Water starts boiling again the syringe was at 95 oC. When the pressure drops the boiling point of the water falls to say 90 oC. Now the water in the syringe is at a higher temperature than the boiling point so it boils. 82 EXTRA STUFF: 83 SECTION A: 1. Increasing the atmospheric pressure on a liquid ………………………………………….. its boiling point. 2. Decreasing the atmospheric pressure on a liquid …………………………………………. its boiling point. 3. Latent heat is the heat required to ………………………………………………………………. ……………………………………………………………………………………………………….. 4. When a substance is changing its state, its temperature ………………………………….. at its ………………………………………………… when melting or freezing and at its …………………………………………………….. when evaporating or condensing. 5. Explain the reasons for the following: (i) Water boils at a lower temperature at the top of a mountain than at the bottom: ………………………………………………………………………………………………. ………………………………………………………………………………………………. (ii) Water can boil at 120 oC in a pressure cooker. ………………………………………………………………………………………………. ………………………………………………………………………………………………. (iii) You can make a hotter cup of tea down a deep mine than at the surface. ………………………………………………………………………………………………. ………………………………………………………………………………………………. 6. (i) Explain why a substance can change state when it is heated. (ii) What are the names given to the two special temperatures at which this happens? (iii) Give an example of these two temperatures for a substance which you know. (iv) Explain why the temperature remains fixed while these changes of states are happening. (v) What is the name of the quantity of heat which is needed to change the state of a substance? 7. Sketch a graph showing the temperature of a solid (for example, ice), against heat added, as it is heated so that it melts and then evaporates. 8. What effect does increasing the atmospheric pressure on a liquid have on its melting point? What happens when the atmospheric pressure decreases? 84 9. A pupil carried out an experiment to plot a cooling curve for lauric acid. The temperature of the lauric acid was recorded at two minute intervals. Draw a diagram showing the apparatus arranged to carry out the experiment and describe what the pupil did before starting to take the measurements. The following table of results was obtained: Time (minutes) 0 2 4 6 8 10 12 14 16 18 Temperature (oC) 83 70 59 50 43 43 43 37 32 28 Draw a graph of the above data, using graph paper. (i) Explain why the graph has the shape which was plotted. (ii) Use the graph to estimate the melting point of the lauric acid. (iii) Mark on your graph where the lauric acid was a liquid, where it was a solid and where it was freezing. (iv) What is the quantity of heat called which was removed from the lauric acid between 8 and 12 minutes? 85 Sample answer to Coursework B question: The following was given as the physics topic for coursework B in 2008: “It is often suggested that denim is an unsuitable fabric to be worn when hill-walking. Investigate the thermal insulation properties of three fabrics, including denim, when wet and dry” 12th February to 17th February Variables which will change during the experiment: 1) Drop in temperature of the water in the cans. 2) Whether the fabric is wet or dry. Variables which must be controlled: 1) Fabrics must be all cut to the same size. 2) Water in each can must start at the same temperature. 3) Same wetting procedure for each fabric. How do I find out how well different fabrics insulate? How do I investigate the effect that being wet has on this? How does denim compare with other fabrics, and what does this tell us about its suitability for hillwalking? This section is best written as one or more questions. I found information on this topic on the following website: Name at least one relevant source that you found (website, book or qualified person not your teacher!). http://www.swanshurst.org/curriculum/attach% 2F18_484_The_Functional_Properties_of_Fabrics_1. pdf which discusses the factors which affect insulation in fabrics. “Controls” here refers to the variables which must not change during the experiment, or which must be identical for each set up. At least four variables must be listed in total Drinks cans, denim and two other fabrics, Thermometers, water, kettle, graduated cylinder, scissors, elastic bands, stopwatch, funnel. At least four pieces of equipment must be listed to gain full marks, but list everything you will use. 1) Measure and cut three identical pieces of different fabrics (one of which is denim). 2) Attach fabric to the can. 3) Put boiling water into the can 4) Record the temperature with time. 5) Repeat whole experiment with each fabric, and then again with each fabric wet. 6) Graph the results of temperature against time. List at least four tasks which you plan to do. This section is similar to the “procedure” section, but is not as detailed. It is supposed to be written before the experiment is carried out. 86 1) Be careful not to burn yourself with the boiling water. Gloves could be used. A funnel will help to avoid spills. 2) Handle the thermometers carefully as if they break you could be cut by broken glass. 3) Use alcohol thermometers instead of mercury as mercury is poisonous if the thermometer breaks. At least two safety precautions must be listed. As with all sections, it is better to include more than the minimum in case one is not accepted. 1) Cut three different fabrics (one denim) to identical sizes that will wrap perfectly once around the cans. 2) Attach one of the fabrics around the can with the elastic bands. 3) Boil water in the kettle. 4) Pour 200 ml of boiling water (measured with the graduated cylinder) into the can. 5) Place a thermometer into the can. Five steps are needed in total (between parts (ii) and (iii)). 6) Wait until the temperature in the can falls to 90 0C (doing this makes sure that the temperature always starts from the same point), and then record the temperature every minute for ten minutes. 7) Repeat the experiment using the other two fabrics. Make sure to use the same volume of water each time. 7) Repeat the whole experiment, except this time soak each fabric in cold water before attaching them to the can. 8) Draw a graph of temperature against time for each fabric, dry and wet. This section is just a continuation of part (ii) on the previous page. You don’t need a second diagram if one will do. Diagrams should be clear and in two dimensions. Label everything, no matter how obvious 87 Temperatures (oC) Time (minutes) Polyester (dry) Nylon (dry) Denim (dry) Polyester (wet) Nylon (wet) Denim (wet) 0 90 90 90 90 90 90 1 85 85 84 83 83 82 2 80 81 78 76 77 75 3 76 77 73 70 71 68 4 72 73 68 64 66 62 5 69 70 64 59 61 56 6 66 68 60 54 56 51 7 64 66 57 50 52 46 8 62 64 54 46 49 42 9 60 62 52 43 46 38 10 58 61 50 40 44 35 Not all experiments will have a table of results, but try to have one if possible. It is easier to analyse numbers than observations. Don’t forget to include the units you are using. Not all experiments will have a graph, but again, it makes the results easier to analyse, so include one if you can. Remember to label both axes and include the units. Scale the axes to make the graph as big as possible. Show the points as circled dots or X’s. Don’t worry if your graph is not as perfect as this one. It can be useful to explain what went wrong in the “errors” section 88 The following temperature drops were obtained: Polyester (dry) = 32 oC Nylon (dry) = 29 oC Denim (dry) = 40 oC Polyester (wet) = 50 oC Nylon (wet) = 46 oC Denim (wet) = 55 oC Bigger drops were recorded when the fabrics were wet. Fabrics which gave a smaller temperature drop were better insulators as they were the slowest to lose their heat. All fabrics were poorer insulators when wet as they gave larger temperature drops than when dry. Nylon was the best insulator, compared either when dry or wet. Polyester was the second best insulator, compared either when dry or wet. Denim was the worst insulator, compared either when dry or wet. The biggest drop of all the trials was for denim when it was wet. This shows that it would not be a suitable fabric to be worn when hill-walking, as if it rained you would lose heat quickly and get cold. You need to either a) draw a graph (on the previous page), b) do some calculations or c) analyse the data. We’ve done all three for safety. The better your analysis, the more marks you get. Here you draw conclusions from your data. In other words explain what your experiment tells you. Again, the better your evaluation, the more marks you get. The experiment could be improved by using the same volume of water to soak the fabrics each time. The fabrics could be soaked in a beaker containing 100 ml of water each time. A possible source of error would be if the fabrics were of different thicknesses. This could be checked with a micrometer. (continued below) (Continued from section 5) A possible extension would be to compare the insulation properties of natural and synthetic fabrics by comparing three natural fabrics (e.g. cotton, linen, silk) to synthetic fabrics (e.g. polyester, nylon, acrylic). Two comments needed on any of: a) How reliable your data was, b) how you could improve your experiment, c) possible sources of error or reasons for unexpected results, d) possible extension to your experiment. Use this part if you run out or space in one of the other sections, but clearly mark which part you are extending (both here and at the relevant section) 89 Junior Cert Science—All the Chemical Equations Instructions: 1. Try to learn the equations on this page. 2. Go to page 2 and fill in the blanks, without looking at page 1 3. Check your answers against page 1 4. Repeat with the other pages. 1. Neutralisation (acid + base → salt + water): Hydrochloric acid + Sodium Hydroxide → Sodium Chloride + Water HCl + NaOH → NaCl + H2O 2. Preparation of Oxygen: Manganese Dioxide Hydrogen Peroxide → Water + Oxygen MnO2 2H2O2 → 2H2O + O2 3. Preparation of Carbon Dioxide: Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon Dioxide + Water CaCO3 + 2HCl → CaCl2 + CO2 + H2O 4. Test for Carbon Dioxide (Lime water test): Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate + Water Ca(OH)2 + CO2 → CaCO3 + H2O 5. Preparation of Hydrogen: Zinc + Hydrochloric acid → Zinc Chloride + Hydrogen Zn + 2HCl → ZnCl2 + H2 90 Now try these yourself: 1. Neutralisation (acid + base → salt + water): Hydrochloric acid + Sodium Hydroxide → Sodium Chloride + Water HCl + NaOH → 2. Preparation of Oxygen: Manganese Dioxide Hydrogen Peroxide → Water + Oxygen MnO2 2H2O2 → 3. Preparation of Carbon Dioxide: Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon Dioxide + Water CaCO3 + 2HCl → 4. Test for Carbon Dioxide (Lime water test): Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate + Water Ca(OH)2 + CO2 → 5. Preparation of Hydrogen: Zinc + Hydrochloric acid → Zinc Chloride + Hydrogen Zn + 2HCl → 91 Now try these yourself: 1. Neutralisation (acid + base → salt + water): Hydrochloric acid + Sodium Hydroxide → Sodium Chloride + Water 2. Preparation of Oxygen: Manganese Dioxide Hydrogen Peroxide → Water + Oxygen 3. Preparation of Carbon Dioxide: Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon Dioxide + Water 4. Test for Carbon Dioxide (Lime water test): Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate + Water 5. Preparation of Hydrogen: Zinc + Hydrochloric acid → Zinc Chloride + Hydrogen 92 Now try these yourself: 1. Neutralisation (acid + base → salt + water): Hydrochloric acid + Sodium Hydroxide → 2. Preparation of Oxygen: Manganese Dioxide Hydrogen Peroxide → 3. Preparation of Carbon Dioxide: Calcium Carbonate + Hydrochloric acid → 4. Test for Carbon Dioxide (Lime water test): Calcium Hydroxide + Carbon Dioxide → 5. Preparation of Hydrogen: Zinc + Hydrochloric acid → 93 Now try these yourself: 1. Neutralisation (acid + base → salt + water): 2. Preparation of Oxygen: 3. Preparation of Carbon Dioxide: 4. Test for Carbon Dioxide (Lime water test): 5. Preparation of Hydrogen: 94