DC & Practical Electricity

Identical power supplies are used in the circuits shown.

Which statement is correct?

• The current in circuit 2 is equal to the current in circuit 1.

• The current in circuit 2 is lower than the current in circuit 1.

• The voltmeter reading is larger in circuit 2.

• The voltmeter reading is the same in both circuits.

A 5 Ω resistor in series with a 10 Ω resistor is connected to a battery of e.m.f. V_B.

There is a current IC through the 5 Ω resistor and the p.d. across it is V₁.

What is the current through and the p.d. across the 10 Ω resistor?

• current = I_C

  p.d = V_B + V₁

• current = I_C / 2

  p.d = V_{B -} V₁

• current = I_C / 2

  p.d = V_B + V₁

• current = I_C

  p.d = V_{B -} V₁

The circuit shows five identical lamps connected to an electrical power supply.

Which current is the smallest?

• A

• B

• C

• D

A student sets up the circuit shown.

The currents measured by the ammeters are shown.

Which equation is correct?

• I₁ = I₂ + I₃ + I₄

• I₁ = I₂ = I₃ = I₄

• I₂ + I₃ = I₄ + I₁

• I₄ = I₃ + I₂ + I₁

Current from an electrical source enters an arrangement of four branches at junction P.

What is the current in branch X?

• 1 A

• 3 A

• 4 A

• 11 A

A lighting circuit used in a house contains 15 lamps connected in parallel. This is the maximum number of lamps that can be used safely.When more lamps are connected in parallel, the circuit stops working.

Why does the circuit stop working?

• The circuit is doubly insulated.

• The connecting wires melt.

• The fuse wire melts.

• The lamps burn out.

An electrician is replacing the damaged plugs attached to a microwave oven in a metal case and a radio in a plastic case.

There are three wires to connect in the plug for the microwave and only two in the plug for the radio.

Which statement explains this?

• The microwave oven has a metal case that needs to be earthed.

• The microwave oven is more powerful so needs an extra wire to supply enough current.

• The radio is less powerful so it does not need a live wire to be connected.

• The radio only needs a live wire and an earth wire to be connected.

The wiring for a home appliance includes a switch and a fuse.

Where are these located?

• switch = live wire

  fuse = live wire

• switch = live wire

  fuse = neutral wire

• switch = neutral wire

  fuse = live wire

• switch = neutral wire

  fuse = neutral wire

When a correctly wired plug is used to connect a working device to the mains, which statement is not correct?

• The fuse is in the live wire connection to the mains.

• The switch is in the live wire connection to the mains.

• The value of the fuse is just larger than the current.

• There is current in the earth wire.

In a household electrical circuit, why are fuses and switches always placed in the live lead?

• A break in the live wire cuts off the appliance from the voltage supply.

• A break in the neutral wire would not stop current in the circuit.

• The live wire carries a greater current.

• The neutral wire carries no current.