Electricity – Potential Difference

Electricity – Potential Difference
GCSE Physics Exam Doctor Electricity – Potential Difference Question 1 Question 2 Question 3 Question 4 Question 5 Question 6

GCSE Physics Exam Doctor Electricity – Potential Difference Question 1

a) What is the sum of the readings of voltmeters V1 and V2? (1 mark)
12v battery variable resistor A lamp fixed resistor R B V1 V2 V a) What is the sum of the readings of voltmeters V1 and V2? (1 mark) b) What does your answer assume about the wire which connects the components? (2 marks)

Predict the reading on V2 and explain why this would happen.
c) If V2 reads 8v what is the potential difference across the variable resistor? (1 mark) d) The fixed resistor R is replaced by one with only half as much resistance. Predict the reading on V2 and explain why this would happen. (3 marks) e) The resistance of the variable resistor is reduced until it is extremely small. Explain how this affects the reading on voltmeter V2. (2 marks) f) If the 12v battery were replaced by a 9v battery, what would be the potential difference between points A and B? (1 mark)

12v battery variable resistor A lamp fixed resistor R B V1 V2 V 12 V a) What is the sum of the readings of voltmeters V1 and V2? (1 mark) b) What does your answer assume about the wire which connects the components? it is made of copper (2 marks)

The reading would rise because it has less resistance
c) If V2 reads 8v what is the potential difference across the variable resistor? 6v (1 mark) d) The fixed resistor R is replaced by one with only half as much resistance. Predict the reading on V2 and explain why this would happen. The reading would rise because it has less resistance (3 marks) e) The resistance of the variable resistor is reduced until it is extremely small. Explain how this affects the reading on voltmeter V2. The reading would go down because it has too much current in it. (2 marks) f) If the 12v battery were replaced by a 9v battery, what would be the potential difference between points A and B? 9v (1 mark)

a) What is the sum of the readings of voltmeters V1 and V2? (1 mark)
Mark scheme 12v battery variable resistor A lamp fixed resistor R B V1 V2 V 12V MP a) What is the sum of the readings of voltmeters V1 and V2? (1 mark) b) What does your answer assume about the wire which connects the components? the wire has little or no resistance 1MP the wire has negligible ( zero) potential difference (PD) between its ends 1MP (2 marks)

Predict the reading on V2 and explain why this would happen.
Mark scheme c) If V2 reads 8v what is the potential difference across the variable resistor? 4v 1MP (1 mark) d) The fixed resistor R is replaced by one with only half as much resistance. Predict the reading on V2 and explain why this would happen. Reading on V2 would fall. 1MP lower resistance would cause a smaller PD across R MP total of PD must remain 12v 1MP (3 marks) e) The resistance of the variable resistor is reduced until it is extremely small. Explain how this affects the reading on voltmeter V2. V2 would rise MP because with low resistance the PD across the variable resistor would fall 1MP (2 marks) f) If the 12v battery were replaced by a 9v battery, what would be the potential difference between points A and B? 9v 1MP (1 mark)

12v battery variable resistor A lamp fixed resistor R B 1 3 V1 V2 V 12 V a) What is the sum of the readings of voltmeters V1 and V2? (1 mark) b) What does your answer assume about the wire which connects the components? it is made of copper The wire may be made of copper but there is no mention of low resistance or low PD across it so no marks (2 marks)

The reading would rise because it has less resistance
c) If V2 reads 8v what is the potential difference across the variable resistor? 6v No mark the PD is = 4v (1 mark) d) The fixed resistor R is replaced by one with only half as much resistance. Predict the reading on V2 and explain why this would happen. The reading would rise because it has less resistance The reading on V2 would fall. One mark for mentioning less resistance. (3 marks) e) The resistance of the variable resistor is reduced until it is extremely small. Explain how this affects the reading on voltmeter V2. The reading would go down because it has too much current in it. Incorrect, the voltmeter reading rises so no mark. The low resistance leads to low PD across the variable resistor so higher PD across the lamp ( total still = 12v) (2 marks) f) If the 12v battery were replaced by a 9v battery, what would be the potential difference between points A and B? 2 7 9v (1 mark)

The diagram shows an electric blanket connected to the mains electricity. The switch S allows the blanket to be switched to high or low settings. When the switch is placed in position A, the current in the circuit is 0.3A a) i) The resistance of the heating element is 600W. Calculate the voltage across the heating element in the blanket. (3 marks)

ii) Calculate the power developed in the blanket when the switch is in position A.
(2 marks) b) When the switch is moved to position B, will the temperature of the blanket increase or decrease? Explain your reasoning. (2 marks)

The diagram shows an electric blanket connected to the mains electricity. The switch S allows the blanket to be switched to high or low settings. When the switch is placed in position A, the current in the circuit is 0.3A a) i) The resistance of the heating element is 600W. Calculate the voltage across the heating element in the blanket. V = I x R = 0.3 x 600 = 180V (3 marks)

ii) Calculate the power developed in the blanket when the switch is in position A.
Power = V x I = 240 x 0.3 = 72W (2 marks) b) When the switch is moved to position B, will the temperature of the blanket increase or decrease? Explain your reasoning. The blanket will get hotter. The electricity is going straight to the blanket instead of through the 200W. (2 marks)

Mark scheme The diagram shows an electric blanket connected to the mains electricity. The switch S allows the blanket to be switched to high or low settings. When the switch is placed in position A, the current in the circuit is 0.3A a) i) The resistance of the heating element is 600W. Calculate the voltage across the heating element in the blanket. V = I x R V = 0.3 x = 180V (3 marks)

Mark scheme ii) Calculate the power developed in the blanket when the switch is in position A. Power = V x I = 180V x 0.3A = 54W (2 marks) b) When the switch is moved to position B, will the temperature of the blanket increase or decrease? Explain your reasoning. Understanding that the whole 240V would now be across the blanket, giving greater power, or that the current through the blanket would be higher. (2 marks)

The diagram shows an electric blanket connected to the mains electricity. The switch S allows the blanket to be switched to high or low settings. When the switch is placed in position A, the current in the circuit is 0.3A a) i) The resistance of the heating element is 600W. Calculate the voltage across the heating element in the blanket. V = I x R = 0.3 x 600 = 180V It would have been equally correct to use the fact that voltage is in the ratio of the resistances i.e. (600/800) x 240V = 180V (3 marks) 3

Scores one for Power = V x I
ii) Calculate the power developed in the blanket when the switch is in position A. Power = V x I = 240 x 0.3 = 72W 240V is not the voltage across the blanket. The figure needed is that from part i) 180V. Power = V x I = 180V x 0.3A = 54W (2 marks) P = I2 R is given at the front of the paper and would yield the correct result 0.3A x 0.3A x 600W = 54W b) When the switch is moved to position B, will the temperature of the blanket increase or decrease? Explain your reasoning. 2 4 The blanket will get hotter. The electricity is going straight to the blanket instead of through the 20O Ohms. (2 marks) “Electricity” is too imprecise. Needs to show understanding that the whole 240V would now be across the blanket, giving greater power, or that the current through the blanket would be higher, or that energy is not being wasted in the resistor.

The circuit shows 2 bulbs connected in series across a 12V supply.
a) i) Lamp A is marked 3V, 0.25A. What does this tell you? (2 marks)

ii) Lamp B is marked 9V, 0.25A. When the lamps are connected as shown, what will voltmeter V1 read?
iii) What will voltmeter V2 read? (1 mark) b) i) Calculate the resistance of lamp A. W (3 marks) ii) What is the total resistance in the circuit? W (2 marks)

a) i) Lamp A is marked 3V, 0.25A. What does this tell you? It tells me that the lamp uses 3V of electricity and needs a current of 0.25A (2 marks)

V1 will read 6V. (1 mark) iii) What will voltmeter V2 read? The voltage V2 will also be 6V, since the voltage is split between the lamps. (1 mark) b) i) Calculate the resistance of lamp A. V = I R = R R = 12 W (3 marks) ii) What is the total resistance in the circuit? 9 = R R = total = 48 W W (2 marks)

Mark scheme The circuit shows 2 bulbs connected in series across a 12V supply. a) i) Lamp A is marked 3V, 0.25A. What does this tell you? The P.D. across a lamp in series with another lamp depends on the resistance of the 2 lamps. The voltage across each will be in the ratio of the resistances. The marking on the lamp tells you what voltage it was designed to be operated on, and if it is operated at that voltage, the current through it will be 0.25A. (2 marks)

Mark scheme ii) Lamp B is marked 9V, 0.25A. When the lamps are connected as shown, what will voltmeter V1 read? The voltage V1 will be 3V . (1 mark) iii) What will voltmeter V2 read? V2 actually reads 9V (12V minus 3V) (1 mark) b) i) Calculate the resistance of lamp A. V = I R R = V/I = 3/ =12 Ohms (3 marks) ii) What is the total resistance in the circuit? For lamp B R = V/I = 9/ =36 Ohms = 48 Ohms (2 marks)

2 a) i) Lamp A is marked 3V, 0.25A. What does this tell you? It tells me that the lamp uses 3V of electricity and needs a current of 0.25A (2 marks) This is a common misunderstanding. The P.D. across a lamp in series with another lamp depends on the resistance of the 2 lamps. The voltage across each will be in the ratio of the resistances. The marking on the lamp tells you what voltage it was designed to be operated on, and if it is operated at that voltage, the current through it will be 0.25A.

V1 will read 6V. (1 mark) Another common mistake, to assume that the lamps are identical. These are not. The voltage V1 will be 3V . iii) What will voltmeter V2 read? The voltage V2 will also be 6V, since the voltage is split between the lamps. (1 mark) V2 actually reads 9V (12V minus 3V) This mark could have been awarded as e.c.f if the pupil had said “ V2 will be 12V minus 6V, but “the voltage being split” shows misunderstanding. 5 7 b) i) Calculate the resistance of lamp A. V = I R = R R = 12 W (3 marks) ii) What is the total resistance in the circuit? 9 = R R = total = 48 W W (2 marks)

The diagram shows two lamps connected in series. Lamp A is marked 2
The diagram shows two lamps connected in series. Lamp A is marked 2.5V 0.3A. Lamp B is a normal 60W mains lamp. a) i) Calculate the resistance of lamp A. (3 marks)

ii) Mains voltage is 240V. What current would the mains lamp take if it were operated normally in a mains circuit? (2 marks) iii) Calculate the resistance of lamp B. (2 marks) b) i) If lamp A were connected in a mains circuit on its own, what would you expect to happen? (1 mark) ii) When lamp A is connected with the mains lamp as shown, what is the Potential Difference across lamp A? (2 marks)

The diagram shows two lamps connected in series. Lamp A is marked 2.5V 0.3A. Lamp B is a normal 60W mains lamp. a) i) Calculate the resistance of lamp A. V = I R = R R = 2.5/0.3 = W (3 marks)

I would expect it to explode.
ii) Mains voltage is 240V. What current would the mains lamp take if it were operated normally in a mains circuit? I = 240/60 = 4A (2 marks) iii) Calculate the resistance of lamp B. V = I R / 4 = 60 W (2 marks) b) i) If lamp A were connected in a mains circuit on its own, what would you expect to happen? I would expect it to explode. (1 mark) ii) When lamp A is connected with the mains lamp as shown, what is the Potential Difference across lamp A? 240V same as across lamp B (2 marks)

Mark scheme The diagram shows two lamps connected in series. Lamp A is marked 2.5V 0.3A. Lamp B is a normal 60W mains lamp. a) i) Calculate the resistance of lamp A. V = I R = R R = 2.5/0.3 = W (3 marks)

Mark scheme ii) Mains voltage is 240V. What current would the mains lamp take if it were operated normally in a mains circuit? I = 60W/240V = 0.25A (2 marks) iii) Calculate the resistance of lamp B. R = 240V / 0.25A = 960Ω (2 marks) b) i) If lamp A were connected in a mains circuit on its own, what would you expect to happen? Lamp fails (1 mark) ii) When lamp A is connected with the mains lamp as shown, what is the Potential Difference across lamp A? The P.Ds are in the ratio of the resistances, so P.D. across lamp A is (8.33/968.33) x 240V = 2.06V (2 marks)

The diagram shows two lamps connected in series. Lamp A is marked 2.5V 0.3A. Lamp B is a normal 60W mains lamp. a) i) Calculate the resistance of lamp A. V = I R = R R = 2.5/0.3 = W (3 marks) 3

I would expect it to explode.
ii) Mains voltage is 240V. What current would the mains lamp take if it were operated normally in a mains circuit? I = 240/60 = 4A It is quite common for pupils who are otherwise quite competent at calculation to get this one upside-down. I = 60W/240V = 0.25A (2 marks) iii) Calculate the resistance of lamp B. V = I R / 4 = 60 W e.c.f The answer is incorrect, but the calculation is correctly done. The error has been penalised in part ii). R = 240V / 0.25A = 960Ω (2 marks) b) i) If lamp A were connected in a mains circuit on its own, what would you expect to happen? I would expect it to explode. Although this is a little extreme, it is sufficient for 1 mark. (1 mark) ii) When lamp A is connected with the mains lamp as shown, what is the Potential Difference across lamp A? 240V same as across lamp B The P.Ds are in the ratio of the resistances, so P.D. across lamp A is (8.33/968.33) x 240V = 2.06V (2 marks)

The diagram shows incorrect wiring for a car’s headlamp and fog lamp.
a) i) Which lamp/s will be lit if switch H is closed, but switch F open? (2 marks) ii) If switch F is closed, while switch H is open, which lamp/s will be lit? (2 marks)

The lamps are designed to light normally on a 12V supply
The lamps are designed to light normally on a 12V supply. In the conditions of a) ii) the lamps will not be lit normally. Explain why not. (2 marks) b) Redraw the diagram so that the lamps are correctly lit and can be turned on/off independently. (3 marks)

The headlamp will be on, but the fog lamp off
The diagram shows incorrect wiring for a car’s headlamp and fog lamp. a) i) Which lamp/s will be lit if switch H is closed, but switch F open? The headlamp will be on, but the fog lamp off (2 marks) ii) If switch F is closed, while switch H is open, which lamp/s will be lit? Fog lamp will be on, but headlamp off. (2 marks)

Because the headlamp is off
The lamps are designed to light normally on a 12V supply. In the conditions of a) ii) the lamps will not be lit normally. Explain why not. Because the headlamp is off (2 marks) b) Redraw the diagram so that the lamps are correctly lit and can be turned on/off independently. 12 V supply Fog lamp Headlamp (3 marks)

Mark scheme The diagram shows incorrect wiring for a car’s headlamp and fog lamp. a) i) Which lamp/s will be lit if switch H is closed, but switch F open? The headlamp will be on, but the fog lamp off (2 marks) ii) If switch F is closed, while switch H is open, which lamp/s will be lit? With F closed, but H open there is a complete circuit for the two lamps in series. They will both be on. (2 marks)

Mark scheme The lamps are designed to light normally on a 12V supply. In the conditions of a) ii) the lamps will not be lit normally. Explain why not. The lamps are in series across a 12V supply, so the lamps share the 12V and will therefore be dim. (2 marks) b) Redraw the diagram so that the lamps are correctly lit and can be turned on/off independently. (3 marks)

The headlamp will be on, but the fog lamp off
The diagram shows incorrect wiring for a car’s headlamp and fog lamp. a) i) Which lamp/s will be lit if switch H is closed, but switch F open? The headlamp will be on, but the fog lamp off (2 marks) ii) If switch F is closed, while switch H is open, which lamp/s will be lit? Fog lamp will be on, but headlamp off. With F closed, but H open there is a complete circuit for the two lamps in series. They will both be on (2 marks) 3 4

Because the headlamp is off
The lamps are designed to light normally on a 12V supply. In the conditions of a) ii) the lamps will not be lit normally. Explain why not. Because the headlamp is off The lamps are in series across a 12V supply, so the lamps share the 12V and will therefore be dim. (2 marks) b) Redraw the diagram so that the lamps are correctly lit and can be turned on/off independently. 12 V supply Fog lamp Headlamp The lamps are correctly in parallel, but with only one switch, they cannot be switched on/off independently. 1 5 (3 marks)

The circuit shows voltmeters used to measure the potential differences across lamps in a circuit.
i) V1 reads 12V. How much energy is changed from electrical energy to heat and light energy for each coulomb of charge which passes through the lamp? (2 marks) ii) The p.d. across the cell (V) is 18V. What will be the reading on voltmeter V2 ? (1 mark)

iii) How much energy is converted into electrical energy in the cell for each coulomb of charge which is drawn from the cell? (2 marks) iv) Are the lamps identical? Explain your answer. (3 marks)

i) V1 reads 12V. How much energy is changed from electrical energy to heat and light energy for each coulomb of charge which passes through the lamp? 12V (2 marks) ii) The p.d. across the cell (V) is 18V. What will be the reading on voltmeter V2 ? 6V (1 mark)

iii) How much energy is converted into electrical energy in the cell for each coulomb of charge which is drawn from the cell? 18V (2 marks) iv) Are the lamps identical? Explain your answer. Yes the symbol shows they are the same.. But the voltage is used before the second one can get it. (3 marks)

Mark scheme The circuit shows voltmeters used to measure the potential differences across lamps in a circuit. i) V1 reads 12V. How much energy is changed from electrical energy to heat and light energy for each coulomb of charge which passes through the lamp? 12 Joules. (2 marks) ii) The p.d. across the cell (V) is 18V. What will be the reading on voltmeter V2 ? 6V (1 mark)

Mark scheme iii) How much energy is converted into electrical energy in the cell for each coulomb of charge which is drawn from the cell? 18 Joules. (2 marks) iv) Are the lamps identical? Explain your answer. No. The lamps have different resistances and the p.d.s across the lamps are in the ratios of the resistances. (3 marks)

2 3 i) V1 reads 12V. How much energy is changed from electrical energy to heat and light energy for each coulomb of charge which passes through the lamp? 12V (2 marks) The unit for energy is Joules. A Volt is the energy transferred in Joules for each coulomb of charge which passes. ii) The p.d. across the cell (V) is 18V. What will be the reading on voltmeter V2 ? 6V (1 mark)

iii) How much energy is converted into electrical energy in the cell for each coulomb of charge which is drawn from the cell? 18V (2 marks) The same mistake with units as before, but since it has already been penalised, both marks awarded. iv) Are the lamps identical? Explain your answer. Yes the symbol shows they are the same.. But the voltage is used before the second one can get it. (3 marks) Shows no understanding of the concept of potential difference in a series circuit. The lamps have different resistances and the p.d.s across the lamps are in the ratios of the resistances. 2 5

GCSE Physics Exam Doctor Electricity – Potential Difference End of questions

Electricity – Potential Difference

Similar presentations

Presentation on theme: "Electricity – Potential Difference"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Electricity – Potential Difference

Similar presentations

Presentation on theme: "Electricity – Potential Difference"— Presentation transcript:

Similar presentations

About project

Feedback