(a) A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ω resistor and a voltage source.

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5 Questions Q1. (a) A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ω resistor and a voltage source. The technician measures the voltage across the LDR and also the current in the LDR. (i) Which one of these circuits should the technician use? Put a cross ( ) in the box next to your answer. (ii) When the LDR is in bright sunlight, its resistance is 185 Ω. The voltage across the LDR is then 7.2V. Show that the current in the LDR is about A. (iii) Complete the sentence by putting a cross ( ) in the box next to your answer. The current in the 120 Ω resistor is

6 A B C D much more than the current in the LDR much less than the current in the LDR the same as the current in the LDR the opposite of the current in the LDR (iv) The technician repeats the readings with the LDR in different light conditions. The table gives two of the readings. Explain why the two current readings are different. *(b) The photograph shows a temporary traffic sign. The traffic sign uses many small lights all powered by a rechargeable battery. These lights need to be very bright during the day so that they can be seen clearly. They do not need to be as bright at night. Explain how using a light-dependent resistor can make the energy stored in the battery last longer. (6)

7 Q2. An inventor is designing a battery-powered torch. She wants the torch to have a brightness control. (a) Which of these could she use in this control? Put a cross ( ) in the box next to your answer. A a diode B a light-dependent resistor

8 C a thermistor D a variable resistor (b) She builds this circuit to test the lamp in the torch. (i) Add a voltmeter to the circuit which will measure the potential difference (voltage) across the lamp. She sets the control at the "bright" position. The current is 0.26 A and the potential difference (voltage) across the lamp is 6.0 V. Calculate the resistance of the lamp. resistance of the lamp = Ω (c) The inventor takes readings of the potential difference (voltage) across the lamp and the current at different positions of the control from "dim" to "bright". She plots a graph of the readings.

9 (i) Complete this graph by plotting the missing point and drawing the curve of best fit. (ii) Describe what this graph shows about how the current changes as the voltage changes. (iii) The lamp gives no light when the brightness control is at its lowest setting. Suggest why the torch would still need an on/off switch as well as the brightness control.

10 (Total for Question = 10 marks) Q3. A student is investigating a filament lamp. (a) (i) Complete the sentence by putting a cross ( ) in the box next to your answer. The current in the filament lamp is a flow of A protons B neutrons C electrons D atoms (ii) The student uses this circuit in his investigation. State what is measured by the meters. Meter 1 measures Meter 2 measures (b) The normal operating potential difference (voltage) and current of the filament lamp is 6 V,

11 0.4 A. Calculate the energy supplied to the lamp under these conditions in 20 s. energy =... J (c) The graph shows how current varies with potential difference (voltage) for another filament lamp. Calculate the resistance of the lamp when the current in the lamp is 0.3 A. resistance = potential difference current (R = V / I) (3) resistance =... Ω (Total for Question = 8 marks) Q4. An inventor is designing a battery-powered torch. She wants the torch to have a brightness control. The inventor takes readings of the potential difference (voltage) across the lamp and the current at different positions of the control from "dim" to "bright".

12 She plots a graph of the readings. (i) Complete this graph by plotting the missing point and drawing the curve of best fit. (ii) Describe what this graph shows about how the current changes as the voltage changes. (iii) The lamp gives no light when the brightness control is at its lowest setting. Suggest why the torch would still need an on/off switch as well as the brightness control.

13 Q5. The photograph shows a device used to measure the amount of light. The circuit diagram shows how the components inside this device are connected. (i) Complete the sentence by putting a cross ( ) in the box next to your answer. The meter used in this circuit is A a voltmeter connected in series with the LDR B a voltmeter connected in parallel with the LDR C an ammeter connected in series with the LDR D an ammeter connected in parallel with the LDR (ii) The amount of light entering the light-dependent resistor (LDR) increases. Which row of the table correctly describes the change in the resistance of the LDR and the

14 change in the current in the circuit? Put a cross ( ) in the box next to your answer. resistance of the LDR current in circuit A increases decreases B increases increases C decreases decreases D decreases increases (iii) The device is used as a light meter. It has a 9 V battery. Calculate the current when the resistance of the LDR is 600 Ω. (3) current =... A (iv) When the light meter has been used for a long time, the meter reading becomes incorrect. Suggest what has happened Q6. (a) The diagram shows an electric circuit with two resistors, R and S.

15 (i) R has a resistance of 11 ohms. Calculate the potential difference across R. potential difference = V (ii) Use information from the diagram to calculate the current in S. current = A (iii) Complete the sentence by putting a cross ( ) in the box next to your answer. A student wants to measure the battery voltage with a voltmeter. The voltmeter should be placed A in series with the battery B in parallel with the battery C in parallel with the ammeter D in series with either resistor R or S

16 (b) Explain why the temperature of a resistor increases when a current passes through it. *(c) A resistor is a circuit component. Two other circuit components are a light dependent resistor (LDR) and a thermistor. Explain how LDRs and thermistors can be used to control the current in a circuit. (6)

17 (Total for Question is 12 marks) Q7. (a) A designer is going to use a thermistor in a temperature gauge. He connects the thermistor into this circuit. He heats the thermistor and measures the current at different temperatures. Here are some of the results plotted on a graph. At 47 C the current was A. (i) Plot this value on the graph.

18 (ii) Draw the curve of best fit through the points. (iii) The supply voltage is 12 V. At 20 C the current is A. Calculate the resistance of the thermistor at this temperature. (3) resistance = Ω (iv) Use this graph of current against temperature to explain the relationship between resistance and temperature for this thermistor. (b) (i) When there is an electric current in a resistor, the resistor gets hot. Explain why the resistor gets hot.

19 (ii) Suggest why the thermistor in a temperature gauge might indicate a temperature slightly higher than the actual temperature of its surroundings. (Total for Question = 10 marks) Mark Scheme Q1.

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21 Q2. Answer Acceptable answers Mark (a) D a variable resistor (b)(i) recognisable symbol such as a box with letter V inside or box with the word voltmeter inside it accept connected in parallel with lamp voltmeter across both lamp and ammeter (b(ii) Substitution R = 6.0 / 0.26 An answer which rounds to 23

22 (c)(i) Evaluation = 23 point correctly plotted at 2.0, 0.14 to within half a small square smooth curve of best fit connecting all given points within half a small square (c)(ii) a description includingtwo of the following: current increases as voltage increases Give full marks for correct answer no working Judge curve by eye. If more than one line present then ignore any that appear to be erased or deleted. Ignore any part of line which goes beyond given points. If plotted point is incorrect then allow ecf for line Allow reverse argument positive correlation (between them ) current is not proportional to the pd gradient gets less (c)(iii) a suggestion to include: graph is not a straight line not in equal steps current does not increase as much (as it gets higher) accept resistance has increased with increase in current for two marks there is still a current (when control is at min position) make the battery last longer to break the circuit to switch the currentoff accept flow of electricity/charge/electrons for current {battery / energy} would be {drained /used up/ wasted} otherwise accept reverse arguments ignore reference to power / volts Q3.

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24 Q4. (i) (ii) Answer Acceptable answers Mark point correctly plotted at 2.0, 0.14 to within half a small square smooth curve of best fit connecting all given points within half a small square a description includingtwo of the following: current increases as voltage increases Judge curve by eye. If more than one line present then ignore any that appear to be erased or deleted. Ignore any part of line which goes beyond given points. If plotted point is incorrect then allow ecf for line Allow reverse argument positive correlation (between them ) current is not proportional to the pd gradient gets less graph is not a straight line not in equal steps current does not increase as much (as it gets higher)

25 (iii) a suggestion to include: accept resistance has increased with increase in current for two marks there is still a current (when control is at min position) make the battery last longer to break the circuit to switch the currentoff accept flow of electricity/charge/electrons for current {battery / energy} would be {drained /used up/ wasted} otherwise accept reverse arguments ignore reference to power / volts Q5. Question Answer Acceptable answers Mark Number (i) C Question Answer Acceptable answers Mark Number (ii) D Question Answer Acceptable answers Mark Number (iii) substitution allow substitution and transposition in either (3) 9 = I 600 order transposition I = 9/600 give full marks for correct answer, no working evaluation = (A) OR =15 ma Question Number (iv) Answer Acceptable answers Mark An explanation linking the following

26 M ( battery voltage has decreased (so) less current (than expected) Q6. Answer Acceptable answers Mark 11x 0.4 (substitution) (a)(i) Full marks for correct answer with 4.4 (V) no calculation (a)(ii) (A) 0.2 or 1/5 (A) (a)(iii) B (b) An explanation linking: electrons {colliding with / bumping into} ions in the lattice /atoms in the metal colliding with other electrons If no other marks scored, allow for 1 mark for "electrical energy {transferred/changed} into thermal/heat energy" do not allow energy being created or produced Indicative Content QWC *(c) A explanation including some of the following points Light dependent resistors (LDR) Thermistor Resistance changes with light intensity Bright light, low resistance No light (dark), high resistance Low resistance gives high current.(ra) Resistance changes with temperature Negative temperature coefficient High temperature, low resistance Low temperature, high resistance Low resistance gives high current (RA) Level 0 No rewardable content a limited explanation linking light affecting LDR AND heat affecting thermistor OR a correct relationship for one device, e.g. thermistors change

27 resistance when the temperature changes and LDRs change resistance when it gets dark OR the {resistance decreases/ current increases} of a LDR when the light gets brighter the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple explanation correctly linking the temperature and light with resistance or current for both devices OR a correct relationship for one device with a link to the way this affects the current and resistance. e.g. the resistance of a LDR increases when the light gets dimmer and when the temperature lowers the resistance of a thermistor increases OR the resistance of a LDR decreases when the light gets brighter and this increases the current the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed explanation including the qualitative relationships for both devices and a link to the way resistance change affects the current in BOTH of them, e.g. the resistance of a LDR is less when the light gets brighter which increases the current. When the temperature lowers the resistance of a thermistor increases. This means that the current will decrease as the thermistor cools down. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors Total for question = 12 marks Q7. Answer Acceptable answers Mark (a)(i) Correctly plotted point +/- ½ a small square (a)(ii) Smooth line through most (at least 5) crosses / points Do not accept clearly dot-to-dot or excessive tramlining Ignore any part of line after 45 (a) (iii) Substitution: transposition and substitution in either(3) order 12 = R Transposition: R = 12/0.047 Evaluation: R = 260 substitution mark can be scored when incorrectly transposed word/symbol equation is given 255.3, 255 give full marks for correct answer no working power of 10 errors with no working score max 1 mark

28 Powered by TCPDF ( (a) (iv) An explanation linking with or current increases with temperature (so) resistance decreases (for this first MP) ignore faster/slower (charge/current) ignore references to heat, current flows more can score both marks by quoting two suitable pairs of values from graph the voltage is constant with For full marks, there must be a (so) resistance decreases (withreference to change of either I or R temperature increase) with temperature (b)(i) An explanation linking {electrons / negative charges} collide with {ions/lattice/electrons} (b) (ii) A suggestion including atoms / nuclei allow for 1 mark,electrical energy transferred to {thermal/heat} energy if no other scored energy transfer in {the thermistor/ any component part of the electrical circuit} causes a rise in temperature of thermistor (above surroundings) thermistor/resistor {gets hot/is heated}