17 Electricity 2020N

What is an electric current in a metal wire?

• a flow of electrons

• a flow of neutrons

• a flow of nucleons

• a flow of protons

Four wires are made of the same metal. Which wire has the greatest resistance?

• a 100 cm long wire with a diameter of 3.0 mm

• a 100 cm long wire with a diameter of 6.0 mm

• a 10 cm long wire with a diameter of 3.0 mm

• a 10 cm long wire with a diameter of 6.0 mm

A student uses four ammeters P, Q, R and S to measure the current in different parts of the circuit shown.

Which two ammeters read the largest current?

• P and Q

• P and R

• R and Q

• R and S

A circuit X is set up with two identical lamps.

Circuit Y is then set up, changing the positions of the meters.

On which meters do the readings change?

• both the ammeter and the voltmeter

• the ammeter only

• the voltmeter only

• neither the ammeter nor the voltmeter

There is a current in a variable resistor when a potential difference (p.d.) is applied across it.

In which situation is the current increased?

• Decrease the p.d. and keep the resistance the same.

• Decrease the p.d. and increase the resistance.

• Keep the p.d. the same and decrease the resistance.

• Keep the p.d. the same and increase the resistance.

The circuit shown includes a battery, three lamps X, Y and Z and three switches S1, S2 and S3.

Lamp X is off but lamps Y and Z are lit. Which switches are closed?

• S1 and S2 only

• S1 and S3 only

• S2 and S3 only

• S1, S2 and S3

An electrical appliance is powered from a mains supply. The appliance normally uses a current of 3 A, but the current briefly rises to 4 A at the instant the appliance is switched on. The cable to the appliance is designed for currents up to 6 A. A fuse is used to protect the circuit.

What should be the rating of the fuse?

• 1A

• 3A

• 5A

• 13A

Each diagram shows part of a circuit.

The circle represents an instrument used to measure the potential difference (p.d.) across the resistor.

Which row is correct?

• amperes, diagram 1

• amperes, diagram 2

• volts, diagram 1

• volts, diagram 2

Three statements about a relay are given. 1. A relay has a coil that becomes a temporary magnet when in operation. 2. A large current in a relay coil is used to switch off a smaller current. 3. A small current in a relay coil is used to switch on a larger current. Which statements are correct?

• 1 and 2 only

• 2 and 3 only

• 1 and 3 only

• 1, 2 and 3

Which statement defines the electromotive force (e.m.f.) of a cell?

• the current in the cell when 1.0 C of charge flows in 1.0 s

• the current supplied by the cell to drive 1.0 C of charge around a complete circuit

• the energy supplied by the cell to drive 1.0 C of charge around a complete circuit

• the energy supplied by the cell to drive 1.0 A of current around a complete circuit