State — 3 marks
A student sets up a simple circuit with a battery, a variable resistor, an ammeter and a voltmeter. They adjust the variable resistor and record the current flowing through the circuit and the potential difference across the resistor.
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(a) State what is meant by the term 'potential difference'.
[1 mark]
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(b) State the relationship between current, potential difference and resistance.
[1 mark]
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(c) When the variable resistor is adjusted to increase its resistance, state what happens to the current flowing through the circuit and explain why using the relationship from part (b).
[1 mark]
Show mark scheme
- (a) The energy transferred per unit charge / work done per unit charge (between two points in a circuit)
- (b) V = IR or potential difference equals current multiplied by resistance / V ∝ I (at constant R) or I ∝ 1/R (at constant V)
- (c) The current decreases because resistance increases, and from V = IR (or I = V/R), if V is constant and R increases, then I must decrease
Show — 2 marks
A student investigates the resistance of a length of nichrome wire. She connects the wire to a variable power supply and measures the current through the wire and the potential difference across it at different settings. At one setting, the ammeter reads 0.75 A and the voltmeter reads 6.0 V.
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Show that the resistance of the nichrome wire is 8.0 Ω.
[2 marks]
Show mark scheme
- Correctly applies R = V/I (or V = IR rearranged) [1 mark]
- Correct substitution of values (6.0 ÷ 0.75 or equivalent) and arrives at 8.0 Ω [1 mark]
State — 2 marks
A student sets up a circuit with a variable resistor (rheostat) connected in series with a fixed resistor and a power supply. As the student adjusts the rheostat, they observe that the ammeter reading decreases while the voltmeter connected across the fixed resistor also decreases.
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(a) State what happens to the total resistance of the circuit as the rheostat is increased.
[1 mark]
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(b) State the relationship between the potential difference across the fixed resistor and the current flowing through it.
[1 mark]
Show mark scheme
- (a) Total resistance increases / Total resistance gets larger
- (b) Potential difference is directly proportional to current / V is directly proportional to I / They have a linear relationship / V = IR
Calculate — 2 marks
A student is investigating how different resistors affect the current in a simple circuit. She connects a 6 V battery to a resistor and measures the current flowing through it. The resistor has a resistance of 12 Ω.
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(a) Calculate the current flowing through the resistor. Use the equation: current = potential difference ÷ resistance
[1 mark]
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(b) The student replaces the resistor with one of resistance 24 Ω. The potential difference remains 6 V. Calculate the new current.
[1 mark]
Show mark scheme
- (a) 0.5 (A) / accept 0.5 A with no working for 1 mark, or correct working (6 ÷ 12 or 0.5) with incorrect or no final answer for 1 mark
- (b) 0.25 (A) / accept 0.25 A with no working for 1 mark, or correct working (6 ÷ 24 or 0.25 or 0.5 ÷ 2) with incorrect or no final answer for 1 mark
Explain — 3 marks
A student sets up a circuit containing a filament lamp and a variable resistor. The student gradually increases the resistance of the variable resistor and observes that the lamp becomes dimmer.
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(a) State what happens to the current in the circuit as the resistance of the variable resistor is increased.
[1 mark]
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(b) Explain why the lamp becomes dimmer when the resistance of the variable resistor is increased.
[2 marks]
Show mark scheme
- (a) current decreases
- (b) increasing resistance decreases current
- (b) less current means less energy transferred to the lamp per second / lamp receives less power
GCSE Perfect