Electromagnetism Review IGCSE

A transformer uses an alternating current (a.c.) supply with an electromotive force (e.m.f.) of 12.0 V to induce an output potential difference (p.d.) of 2.0 V.

The output of the transformer is connected to a lamp. The current in the lamp is 100 mA. The transformer is 100% efficient.

Calculate the input current to the transformer.

• 0.017 A

• 0.07 A

• 600 mA

• 0.00017 A

The diagram shows a transformer connected to an input voltage of 12 V a.c. Using the information in the diagram, calculate the output voltage of the transformer.

• 18 V

• 15 V

• 180 V

• 1800 V

The diagram shows a transformer connected to an input voltage of 12 V a.c. How does the diagram show a step-up transformer?

• More turns on the primary coil.

• More turns on the secondary coil.

• There is a core.

• There is an input voltage.

The diagram shows an electrical device. The coil rotates in a magnetic field when connected to a d.c. power supply. State the name of the electrical device shown in the diagram.

• d.c. motor

• a.c. generator

• transformer

• magnet

Each of the three diagrams shows a current-carrying conductor and a magnetic field pattern. State the diagram which correctly shows the magnetic field around a current-carrying conductor.

• A

• B

• C

A student connects a lamp and centre-zero galvanometer in series with a generator, as shown in the diagram. The student observes the galvanometer needle moving from side-to-side repeatedly. Why?

• There is an a.c. current.

• It is being effected by a magnet.

• The lamp is damaged.

• It is an error.

The diagram shows a transformer that can provide two different output voltages from a 240 volt mains a.c. supply. In the transformer, the primary coil has 5000 turns. The secondary coil has 250 turns between P and R. State the term used to describe this type of transformer.

• Step-up transformer.

• Step-down transformer.

• Step-around transformer.

• Step to the left transformer.

The diagram shows a desktop computer. The computer is connected to a mains supply by a plug containing a fuse. The computer contains a transformer. The input voltage to the transformer is 240 V and the output voltage is 12.0 V. The input coil of the transformer has 3000 turns.

Calculate the number of turns on the output coil.

• 300

• 150

• 24

• 450

The diagram shows a simple alternating current generator. Which two possible changes would cause a larger e.m.f. to be induced.

• stronger magnets, more turns.

• weaker magnets, more turns.

• increase speed, fewer turns.

• more turns, reduce speed.

• 0.05 A

• 0.0005 A

• 0.005 A

• 5 A