The Physics Question Bank

Question 01

A student investigates how the length of a wire affects its resistance. She measures the current and potential difference for different lengths and calculates the resistance. Table 1 shows her results.

Length (cm)	20	40	60	80	100
Resistance (Ω)	1.0	2.0	3.0	4.0	5.0

01.1 Describe the relationship between length and resistance. Use data from Table 1.    [2 marks]

Mark scheme

resistance is directly proportional to length (1)
e.g. doubling the length from 20 cm to 40 cm doubles the resistance from 1.0 Ω to 2.0 Ω (1)

01.2 Predict the resistance of 150 cm of the same wire.    [1 mark]

Mark scheme

7.5 Ω (1)

01.3 Explain why the student should use a low potential difference and switch off between readings.    [2 marks]

Mark scheme

a current heats the wire / the wire’s temperature rises (1)
which increases its resistance, so temperature would become a second variable (1)

01.4 Another student’s graph of resistance against length is a straight line, but it does not pass through the origin. It crosses the resistance axis at 0.3 Ω.
Suggest a reason for this.    [2 marks]

Mark scheme

a systematic error / zero error (1)
e.g. the resistance of the connecting leads or crocodile clips is added to every reading / the first clip was not at 0 cm (1)

Question 01 total: 7 marks

Question 02

A 4.0 Ω resistor and a 6.0 Ω resistor are connected in parallel to a 12 V supply.

02.1 Calculate the current from the supply.    [3 marks]

Mark scheme

current in 4.0 Ω = 12 ÷ 4.0 = 3.0 A (1)
current in 6.0 Ω = 12 ÷ 6.0 = 2.0 A (1)
total current = 5.0 A (1)

02.2 Calculate the total resistance of the circuit.    [1 mark]

Mark scheme

R = 12 ÷ 5.0 = 2.4 Ω (1)
allow error carried forward from 02.1

02.3 Explain why the total resistance is less than the resistance of either resistor on its own.    [2 marks]

Mark scheme

adding a resistor in parallel gives the current another path (1)
so the total current increases for the same potential difference, so the total resistance decreases (1)

Question 02 total: 6 marks

Question 03

An electric car is charged at home. The charging cable carries a current of 32 A for 6.0 hours.

03.1 The cable has a resistance of 0.050 Ω.
Calculate the power wasted heating the cable.
Use the equation: P = I² R    [2 marks]

Mark scheme

P = 32² × 0.050 (1)
P = 51 W (1) – allow 51.2 W

03.2 Calculate the charge that flows during the 6.0 hours. Give your answer in standard form.    [3 marks]

Mark scheme

6.0 hours = 21 600 s (1)
Q = 32 × 21 600 = 691 200 C (1)
Q = 6.9 × 10⁵ C (1) – standard form mark

03.3 The charger has a power of 7.4 kW.
Calculate the energy transferred in 6.0 hours. Give your answer in standard form.    [2 marks]

Mark scheme

E = 7400 × 21 600 (1)
E = 1.6 × 10⁸ J (1) – allow 1.5984 × 10⁸ J

Question 03 total: 7 marks

Question 04

A fire alarm uses a thermistor in series with a 1000 Ω fixed resistor and a 9.0 V battery. At 60 °C the resistance of the thermistor is 200 Ω.

04.1 Calculate the potential difference across the fixed resistor at 60 °C.    [4 marks]

Mark scheme

total resistance = 1000 + 200 = 1200 Ω (1)
I = 9.0 ÷ 1200 (1)
I = 0.0075 A (1)
V = 0.0075 × 1000 = 7.5 V (1)

04.2 Explain why the potential difference across the fixed resistor increases as the temperature rises.    [2 marks]

Mark scheme

the resistance of the thermistor decreases, so the total resistance decreases and the current increases (1)
so the potential difference across the fixed resistor increases (V = I R) (1)
allow: the thermistor takes a smaller share of the supply p.d.

Question 04 total: 6 marks

Question 05

Electricity from power stations is transmitted to homes through the National Grid.

05.1 Explain how the National Grid transmits electricity efficiently and safely. Refer to step-up and step-down transformers in your answer.    [6 marks]

Mark scheme

Level 3 (5–6 marks): a clear, logical explanation of why a high p.d. makes transmission efficient, linked to the role of both types of transformer and to safety.
Level 2 (3–4 marks): the roles of the transformers are described, with some explanation of efficiency or safety.
Level 1 (1–2 marks): simple statements about transformers or the National Grid.
0 marks: no relevant content.

Indicative content:
• step-up transformers increase the p.d. from the power station to the transmission cables
• for the same power, a higher p.d. means a smaller current (P = V I)
• a smaller current means less energy is wasted heating the cables (P = I² R)
• so transmission is more efficient
• step-down transformers decrease the p.d. to a safer level (230 V) for use in homes
• very high p.d. would be dangerous in homes / high-voltage cables are kept high up on pylons

Question 05 total: 6 marks

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END OF TEST. Total: Separate Physics 39 marks · Combined Science 32 marks.

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