Practical Electricity (Cambridge O Level Physics)

The plug for an electric lamp contains a 3 A fuse. The fuse’s job is to protect the lamp if too much current flows.

Where is the fuse positioned, and what happens when the fuse does its job?

Which of the diagrams below shows a fuse which has been correctly connected to a circuit?

Both fuses and circuit breakers are devices which protect devices from high currents that could cause them to get too hot and catch fire.

The diagram shows two possible positions where a fuse or a circuit breaker could be positioned.

Which location would be suitable for a fuse, and which would be suitable for a circuit breaker?

The diagram shows two bulbs, which have been connected in parallel. A fuse has been included in the circuit.

Each of the ammeters reads 1.2 A.

What fuse should be put in this circuit?

The fuse blows in a kettle, and the owner of the kettle, Brooke Bond decides to replace the fuse. The fuse he takes out has 13 A written on it. 

Brooke does not have any fuses in the cupboard with 13 A written on them, so he replaces it with a fuse that has 3 A written on it.

He then switches the kettle on to make a nice cup of tea. What happens?

The diagram shows a toaster that has been wired up.

Three fuses have been connected to the toaster, but only one or two have been connected correctly.

Which of the fuses has been positioned correctly?

An oven is wired into somebody’s kitchen. The oven is protected by a fuse, and functions normally, but the owner notices that the wires that connect the oven to the mains electricity supply get quite hot.

What could be done to reduce the temperature of the wires?

A student sets up the circuit below, it contains four fuses and four bulbs.

She finds that none of the bulbs are lit, but only one of the fuses has blown.

Which fuse has blown?

The e.m.f. of the battery in a radio is 3.0 V. 

The resistance of the circuit in the radio is 6.0 Ω. 

The radio is switched on.

How much energy is transferred from the battery in 30 minutes?

What is the unit for the energy used by an electrical appliance?

A 100W lamp is switched on for five hours each day for three weeks. 

The cost of one unit of electricity is $0.24. 

How much does it cost to run the lamp for this time?

The information on the back of an electric room heater is shown.

What is a suitable fuse rating for this room heater?

A person wants to install a circuit breaker to protect themselves and their lawnmower from too much current.

Under normal operating conditions, the lawnmower carries 4 A of current.

The manufacturer provides the graph below with the circuit breaker.

What will happen when the current is 4 A, and what will happen if the current rises to 14 A?