AQA GCSE Physics: Electricity

A polythene rod is rubbed with a dry duster. After rubbing, the rod is found to carry a negative electrostatic charge, and it can attract small pieces of paper. (This is Higher-tier content.)

Describe and explain, in terms of the movement of electrons, how the polythene rod becomes negatively charged, and explain why a charged rod is able to attract small uncharged pieces of paper. (6 marks)

A torch bulb is connected to a battery. A charge of 180 C flows through the bulb in 4.0 minutes, and the potential difference across the bulb is 3.0 V.

(a) Calculate the current through the bulb. Use $Q = It$Q=It (convert the time to seconds first). Show your working and give the unit. (2 marks)

(b) Calculate the energy transferred by the bulb in this time. Use $E = QV$E=QV. (2 marks)

An electric immersion heater has a resistance of 19 Ω and carries a current of 12 A.

(a) Calculate the power of the heater. Use $P = I^2R$P=I2R. Show your working and give the unit. (2 marks)

(b) State one reason why this heater would be unsuitable to run from a plug fitted with a 3 A fuse. (1 mark)

Two resistors, R₁ = 6 Ω and R₂ = 3 Ω, are connected in parallel across a 9.0 V supply.

(a) Calculate the total resistance of the two resistors in parallel. Use $\dfrac{1}{R_T} = \dfrac{1}{R_1} + \dfrac{1}{R_2}$RT​1​=R1​1​+R2​1​. (2 marks)

(b) State how the potential difference across $R_1$R1​ compares with the potential difference across $R_2$R2​. (1 mark)

A thermistor is used as the temperature sensor in a thermostat that switches a heater on and off.

Explain how the resistance of a thermistor changes as its temperature rises, and state what happens to the current through it (for a fixed potential difference). (2 marks)

The National Grid uses transformers to change the potential difference of the electricity supply between power stations and homes.

Name the type of transformer used at a power station to raise the potential difference for transmission across the country. (1 mark)