Electricity 1: Circuits Basics Write a definition for the following terms: Current ……………………………………………………………………………..…………………………………………………………. ……………………………………………………………………………..…………………………………………………………. Voltage ……………………………………………………………………………..…………………………………………………………. ……………………………………………………………………………..…………………………………………………………. Resistance ……………………………………………………………………………..…………………………………………………………. ……………………………………………………………………………..…………………………………………………………. Calculate the number of electrons required to carry a charge of 1 Coulomb. …………………………… Equation 1 βπ πΌ= βπ‘ Explain what each of the terms stand for including units or values as necessary. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Write what this equation physically means (in terms of the relationship between the variables). ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Rearrange the equation to make Q and then t the subject. π= π‘= Complete these tables by calculating the missing values. I 3 0.4 Q t 180 18 57 160 I 0.015 0.7 Q t 0.6 36 107 40 Equation 2 π π= π Explain what each of the terms stand for including units or values as necessary. ……………………………………………………………………………….………………………………………………… ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Write what this equation physically means (in terms of the relationship between the variables). ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Rearrange the equation to make W and then Q the subject. π= π= Complete this table by calculating the missing values. V 17 2400 W Q 72 0.6 3 V 1.5 1825 500 000 W Q 600 30 4.3 175 000 Equation 3 – Ohm’s Law π π = πΌ Explain what each of the terms stand for including units or values as necessary. ……………………………………………………………………………….……………………………………………………. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Write what this equation physically means (in terms of the relationship between the variables). ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Rearrange the equation to make V and then I the subject. π= πΌ= Complete these tables by calculating the missing values. V 9 6 I R 0.5 18 3 2 V 8 230 I R 0.25 1.2 120 0.05 State what is meant by the term ‘a non-ohmic conductor’. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Electricity 2: I-V Graphs Symbol Name What it does …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………………… Complete this diagram to show the set up required to obtain the results needed to plot an I-V graph of a filament lamp. What quality does an ideal voltmeter have? ……………………………………………………………………………………... What quality does an ideal ammeter have? ……………………………………………………………………………………... What is the purpose of the extra component that you have included? ……………………………………………………………………………………... ……………………………………………………………………………………........................................................................................... ……………………………………………………………………………………........................................................................................... Sketch the I-V graphs of the following components and describe what each one shows. Ohmic Conductor ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. Filament Lamp ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. Semiconductor Diode ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. Complete this graph to show how the resistance of an LDR changes when the light levels are increased. Complete this graph to show how the resistance of a thermistor changes when it is warmed up. Choose one graph and describe the relationship between the variables. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Electricity 3: Resistivity The resistance of a metal wire is caused by free electrons colliding with the positive ions that make up the structure of the metal. The values of the resistance depends upon several factors. For each factor describe how it changes the resistance and explain how this happens. Length …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. Area …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. Temperature …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. Material (structure) …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. …………………………………………………………………………………..…………………………………………………………………….. The resistivity of a material accounts for the structure and temperature; every material has its own value of resistivity for each temperature. The resistivity is given by the following equation: Use this space to deduce the units of ρ π π΄ π= πΏ Symbol π Quantity …………………………………………………………………………………………… Units ……………………… Symbol π Quantity …………………………………………………………………………………………… Units ……………………… Symbol π΄ Quantity …………………………………………………………………………………………… Units ……………………… Symbol πΏ Quantity …………………………………………………………………………………………… Units ……………………… Rearrange the equation to make the following the subject: π π΄ πΏ Complete this table by calculating the missing values. ρ 4.0 × 10-3 1.7 × 10-7 6.8 × 102 2.8 × 103 1.1 × 10-7 5.3 × 10-7 R 0.075 1.6 × 10-3 7.0 × 10-2 45 0.93 4.1 × 104 Reading from a micrometer screw gauge. Radius A 2.28 × 10-7 7.9 × 10-5 4.52 × 10-4 1.3 × 10-7 L 1.20 0.75 6.0 × 10-2 7.5 × 10-1 12.2 4.8 7.85 × 10-7 1.25 × 10-5 In every scale the 5 represent a measurement of 5 mm. Area Radius Area Radius Area Radius Area A sample of conducting putty is shaped into a cylinder with a length of 6 cm and a radius of 1.2 × 10-2 m. What would happen to the resistance of the putty if the was rolled into a cylinder of double the radius? ……………………………..…………. Electricity 4: Superconductivity Metals The resistance of a metal is caused by the interactions (collisions) of moving electrons with the fixed positive ions of the metal. Use these diagrams to help you describe and explain how the resistance of a metal changes when the temperature is increased. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… Insulators Insulators have no mobile electrons and so a current cannot flow through them. Semiconductors Semiconductors have a limited number of mobile electrons. Describe and explain what happens when a semiconductor is heated. Sketch and label a graph to support your description. ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... Semiconductors are used to produce thermistors. List the uses of thermistors. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Choose one of the uses that you have listed. Explain how or where it is used, evaluate the benefits and drawbacks of using the semiconductor in this way. Include a circuit diagram if you can. ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… ……………………………………………………………………………….………………… Superconductors Describe what a superconductor is and when it superconductors. Sketch and label a graph to support your description. ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... ………………………………………………………………………….... Lord Kelvin thought that cooling a metal to very low temperatures would mean that it would have an infinite resistance and be a perfect insulator. Explain why this would be so. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. List the uses of superconducting materials. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Why are scientists attempting to find or create a superconductor that superconducts at room temperature? ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Choose one of the uses that you have listed. Explain how or where it is used and evaluate the benefits and drawbacks of using the superconductor in this way. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Electricity 5: Series and Parallel This diagram shows three resistors connected in series. Complete these equations to show how the potential difference and current behave in a series circuit: ππ΅ππ‘π‘πππ¦ π1 π2 π3 πΌπ΅ππ‘π‘πππ¦ πΌ1 πΌ2 πΌ3 If you know the overall (or combined) resistance and know the potential difference of the battery we can work out the total current of the circuit. To find the voltage across one of the resistors you would use the equation: π = πΌπ The value of the resistance will be given in the question and current can be deduced. This diagram shows three resistors connected in parallel. Complete these equations to show how the potential difference and current behave in a parallel circuit: ππ΅ππ‘π‘πππ¦ π1 π2 π3 πΌπ΅ππ‘π‘πππ¦ πΌ1 πΌ2 πΌ3 If you know the overall (or combined) resistance and know the potential difference of the battery we can work out the total current of the circuit. To find the current through one of the resistors you would use the equation: π = πΌπ The value of the resistance will be given in the question and potential difference can be deduced. Cells connected in series Calculate the total potential difference provided by the cells. Each cell is 1.5V. Identical cells connected in parallel Calculate the total potential difference provided by the cells. Each cell is 6V. …………………………………… ……………………………………. …………………………………… …………………………. …………………………. Cells in series provide a higher potential difference but a smaller current. …………………………. Cells in parallel provide a lower potential difference but a larger current. You can calculate the total resistance of resistors connected in series using the following equation: π π = π 1 + π 2 + π 3 RT R1 10 400 150 12 7500 R2 15 25 175 3 3000 R3 20 540 0 4 2500 You can calculate the total resistance of resistors connected in parallel using the following equation: 1 1 1 1 = + + π π π 1 π 2 π 3 RT 12 7500 R1 10 400 100 R2 15 25 175 3 3000 R3 20 540 0 4 2500 What can be concluded about the total resistance compared to the individual resistors connected in parallel? ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. You have been given only three resistors or fixed values 10β¦, 25β¦ and 40β¦. Calculate all the possible resistances that could be created using one, two or all of these resistors. Draw how they are connected. Electricity 6: Energy in Circuits Symbol E Quantity …………………………………………………………………………………………… Units ……………………… Symbol P Quantity …………………………………………………………………………………………… Units ……………………… Symbol V Quantity …………………………………………………………………………………………… Units ……………………… Symbol I Quantity …………………………………………………………………………………………… Units ……………………… Symbol R Quantity …………………………………………………………………………………………… Units ……………………… Symbol t Quantity …………………………………………………………………………………………… Units ……………………… Equations from lesson E1: 1 βπ πΌ= βπ‘ 2 πΈ π= π 3 π π = πΌ Define the term ‘power’…..……………………………………………………………………………………………………………………..….. ……………………………………………………………………………….……………………………………………………………………….. The power is given by the equation below on the left. Use the equations from lesson E1 to derive the following equations: πΈ π= π‘ πΈ π= π‘ πΈ π= π‘ π = ππΌ π = πΌ2 π π2 π= π Rearrange the equations above to make V, I and then R the subject. π= πΌ= π = π= πΌ= π = Derive three equations for the E from the power equations above. Complete this table by calculating the missing values. E 130 P I 0.20 V 12 Q 230 5.7 3.2 375 88 t 25 470 0.89 175 11 12 260 15 66500 R 56 0.50 38 33 × 106 Describe what happens to the current and the potential difference in the National Grid and explain why this increases efficiency. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Describe and explain other changes that can be made to reduce energy loses within a circuit. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. 24 identical 6 V batteries can be used to power a motor and could be connected in series or in parallel. The power required by the motor is 6 kW and the connecting wires have a resistance of 0.005 β¦. Calculate: a) the current through the motor b) the power lost in the wires and c) the efficiency of energy transfer. Series Parallel Explain the advantages and disadvantages of both. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Electricity 7: Potential Dividers Kirchhoff’s 1st Law (Current). ……………………………………………………………………………….…………………………. ……………………………………………………………………………….…………………………. ……………………………………………………………………………….…………………………. Kirchhoff’s 2nd Law (Energy). ……………………………………………………………………………….…………………….…… ……………………………………………………………………………….………………….……… ……………………………………………………………………………….…………………….…… Below is a diagram of the most basic potential divider. Describe the structure of all potential dividers. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Potential dividers do not share the potential equally, they share it fairly. If R1 contributes 30% of the total resistance then it will receive ……………….. of the voltage from the battery. If R2 contributes 1/6 of the total resistance then it will receive ……………….. of the voltage from the battery. π1 = π2 = All of the resistors in the diagram below have the same value. What would the reading be if a voltmeter was connected between the following points: A and B? B and C? A and C? A and D? E and F? F and G? G and E? A and F? B and F? C and E? B and G? D and E? G and C? B and B? Potential dividers often have either a variable resistor, LDR or a thermistor. Complete this graph to show how the resistance of an LDR changes when the light levels are increased. B and D? Complete this graph to show how the resistance of a thermistor changes when it is warmed up. Describe and explain what happens as the resistance of the variable resistor is slowly increased from very low to very high. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. Describe and explain what happens as the temperature drops from a high to low temperature. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. Describe and explain what happens as the light levels are slowly decreased from brightest to darkest. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. Complete this table by calculating the missing values. Vin 6.0 R1 8.0 R2 4.0 12 20 60 8.0 100 230 30 7.2 V2 1.0 28.8 900 16 5.0 V1 3.6 12 5.0 56 1.75 5000 1.25 2.2 3.75 10 6300 3700 3.3 5.67 Give your answers to the appropriate number of significant figures. Electricity 8: EMF and Internal Resistance Define the following terms: Electromotive force (emf) ……………………………………………………………………….……………………………………………..….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Internal resistance ……………………………………………………………………………….……………………………………………..….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Terminal potential difference ..………………………………………………………………….……………………………………………..….. ……………………………………………………………………………….……………………………………………………………………….. The emf of a cell or battery can be calculated using the following equation: π = πΌ(π + π) Rearrange the equation to make the following the subject: πΌ π π The emf of a cell or battery can also be calculated using the following equation: π = π + πΌπ Rearrange the equation to make the following the subject: π πΌ π Explain what each of the terms stand for including units or values as necessary. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Complete this table by calculating the missing values. ε V 0.6 I 2 1.4 9 5.7 12 15 25 6.0 R 0.8 7 0.74 800 11 21 5.8 650 10 r 0.45 3.1 2 1.5 5 × 10-3 9.5 × 10-3 Complete and label this diagram to show the quantities from the equations and how measurements are taken from the circuit. Rearrange the equation π = π + πΌπ to show what the gradient and y-intercept represent. Gradient ……………………… Y-intercept ……………………… Describe what the graphs below show about the relationship between the terminal pd and the current of a cell. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Explain why this happens. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Here is the graph obtained from a particular cell. For each change described below sketch the new graph that would be obtained. 1) The cell has a lower emf and a higher internal resistance. 2) The cell has a higher emf and a lower internal resistance. 3) The cell has a lower emf and negligible internal resistance but the external resistances are all halved. State and explain the change that would be needed to the circuit diagram to obtain kind of graph shown above. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Why is it important that car batteries have a very low internal resistance? ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. ……………………………………………………………………………….……………………………………………………………………….. Show why the theory of special relativity doesn’t allow a matter particle to travel as fast as the speed of light. ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….……………….. Energy As we have seen in Nuclear Physics, energy is connected to mass by the equation πΈ = ππ 2 . This now becomes: π0 π 2 2 πΈ = ππ = π£2 √1 − π2 Kinetic Energy At relativistic speeds we can’t use the equation πΈπΎ = ½ππ£ 2 to calculate the kinetic energy since the mass increases. We have to calculate the rest energy, the relativistic energy and the difference is the kinetic energy. Write an equation for calculating kinetic energy. A proton is accelerated from rest through a pd V to a speed 0.92c. Calculate: a) the mass of the proton at this speed b) its kinetic energy at this speed c) the accelerating pd, V. Bertozzi’s Experiment How was the speed of the electrons arriving at B calculated? ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….……………….. How was the kinetic energy of the electrons calculated? ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….……………….. ………………………………………………………………….…………….……………………………………………………….………………..
