Electric Circuits & Electrical Safety (CIE IGCSE 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?

	Where is it positioned?	What does it do?
A	live wire	reduces the current to 3 A
B	neutral wire	breaks the circuit
C	live wire	breaks the circuit
D	neutral wire	reduces the current to 3 A

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?

	fuse	circuit breaker
A	P	P
B	P	Q
C	Q	P
D	Q	Q

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?

A surge of current in a kettle melts the 13 A fuse.

What will happen to the kettle next time it is used if the fuse is replaced with a 3 A fuse?

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?

The diagram shows two resistors connected in series with a battery.

What is the current through the battery?

A book shop owner sets up the circuit below, but they find that the lamp is too dim.

What change can be made to the circuit to increase the brightness of the bulb?

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?

Extended tier only

A homeowner buys a security light that switches on automatically when it gets dark.

The security light contains the circuit, shown below.

When it gets dark, what happens to the resistance of the LDR, and what happens to the potential difference across the LDR?

	Resistance of LDR	p.d. across LDR
A	increases	increases
B	decreases	increases
C	increases	decreases
D	decreases	decreases

Extended tier only

Two resistors are connected in parallel.

What is the combined resistance of the combination?

Extended tier only

Two resistors are connected in parallel.

The current through the top resistor is 2.0 A.

What is the reading on the ammeter?

Extended tier only

A 10 Ω and a 30 Ω resistor are connected in series, as shown in the diagram below, making a potential divider circuit.

What would be the reading on the voltmeter?

Which of the following statements about the current in ammeters X, Y and Z is correct?

Extended tier only

All the light bulbs in the diagrams above are identical. Each one is rated as ‘10 W, 230 V’.

In which of the diagrams are all the bulbs working at their normal brightness?

A student connects together some identical resistors in three different combinations, as shown in the diagram.

Which of the answers below shows the correct order of the combinations from the lowest resistance to the highest?

A teacher writes a set of notes about two non-identical bulbs which are connected in parallel.

He makes one mistake. Which of the statements below is incorrect?

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?

	4 A	14 A
A	circuit does not break	circuit does not break
B	circuit does not break	circuit breaks quickly
C	circuit breaks quickly	circuit does not break
D	circuit breaks quickly	circuit breaks quickly