igcse

The diagram shows a bar magnet at rest on a smooth horizontal surface. A length of soft-iron wire is held parallel to the magnet. The wire is released. What happens?

• The wire moves away from the magnet.

• The wire moves towards the magnet.

• The wire’s centre stays in its present position and the wire rotates through 90° in a clockwise direction.

• The wire’s centre stays in its present position and the wire rotates through 90° in an anticlockwise direction.

A laboratory has a standard wire of known resistance. It also has other wires, made from the same material as the standard wire, but of different lengths and diameters. Which wire would definitely have a resistance of less than the standard wire?

• A

• B

• C

• D

What is the combined resistance of the resistors?

• 0.14Ω

• 0.57Ω

• 1.7Ω

• 7.0Ω

The diagram shows a circuit which includes two resistors and a battery. The voltmeter reads 6.0V. What is the potential difference across the 30Ω resistor?

• 2.0V

• 6.0V

• 18V

• 24V

A wire is moved down in a direction perpendicular to the magnetic field. Three changes are suggested. Which changes increase the electromotive force (e.m.f.) induced in the wire?

• 1 and 3

• 1 only

• 2 and 3

• 3 only

A 100% efficient step-down transformer has primary voltage Vp and primary current Ip. Which row compares the secondary voltage with Vp and the secondary current with Ip?

• A

• B

• C

• D

A machine has a power input of 200W and a useful output energy of 1 kJ in 6 minutes. What is the efficiency of the machine?

• 0.014%

• 0.83%

• 1.4%

• 83%

What is the unit of power?

• joule

• newton

• volt

• watt

Which circuit symbol represents a component used to measure electric current?

• A

• B

• C

• D

There is a current I in a resistor. The potential difference (p.d.) across the resistor is V. Which other physical quantity is needed to be able to determine the energy transferred W by the resistor?

• the time t for which there is a current in the resistor

• the resistance R of the resistor

• the electromotive force (e.m.f.) E of the source

• the power P dissipated