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