energy & voltage in circuits

explain how the student can work out the resistance of the LDR using this circuit (2 marks)

• measure current

• divide voltage reading by current reading (resistance = voltage/ current)

describe the relationship between the resistance of the LDR & the diameter of the hole (2 marks)

• idea of an inverse relationship (e.g. the bigger the diameter the lower the resistance)

• idea of a non-linear relationship

suggest why the wires in the clothes iron cable are thicker than the wires in the lamp cable (1 mark)

• carries a higher current

• has lower resistance

which of these wires is connected to the fuse? (1 mark)

L or Live

suggest why the lamp is safe to use, even though its cable only has 2 wires (1 mark)

• double insulated

• has a plastic case

a student investigates the current in a thermistor at different temperatures. give a reason for keeping the voltage across the thermistor constant (1 mark)

because voltage is a controlled variable

a student investigates the current in a thermistor at different temperatures. give a reason for including the variable resistor in the circuit (1 mark)

• idea of adjustment of current or circuit resistance

• to control the current

how can you tell that the resistance of the filament lamp changes as the voltage is increased? (1 mark)

idea that gradient changes

explain the changes in resistance of the filament lamp as voltage is increased (3 marks)

• lamp heats up

• greater chance of electron collisions

• hence resistance increases

explain why the resistance of the filament lamp changes as the voltage is increased (3 marks)

• lamp heats up

• greater chance of electron collisions

• hence resistance increases