Practical Electricity

Calculate the current in the heater.

current = ______ $\text{A}$

The manufacturer of the kettle states that the cable for the kettle is safe for currents that are smaller than $15\ \text{A}$. The wiring in the mains power supply in the wall is safe for currents that are smaller than $20\ \text{A}$.

The fuses available for the kettle have the ratings shown.

State which of these fuses is the most appropriate. Explain why it is the most appropriate.

most appropriate fuse rating = ______ $\text{A}$

explanation ______

State the name of the wire that the fuse is connected into. Explain why the fuse is connected into this wire.

name of wire ______

explanation ______

The insulation on the live wire is damaged so that the wire is exposed.

Explain what happens when the exposed live wire touches the metal outer casing.

The kettle is switched on for a total time of $34\ \text{h}$ during one year.

The cost of electricity is $0.32 per kilowatt-hour (kWh).

Calculate the cost of using the kettle during the year.

cost = $ ______

the neutral wire in the cable

current in neutral wire = ______

the earth wire in the cable.

current in earth wire = ______

Explain how the earth wire and the fuse together prevent any more damage.

Explain why it is the live wire into which the fuse is connected.

The boxes in the left column below contain some electrical hazards. The boxes in the right column contain methods of protection from these hazards.

For each hazard, draw one line to the appropriate method of protection.

Define the kilowatt-hour ($\text{kW\,h}$).

The iron is on at full power for $20\ \text{minutes}$.

Calculate the cost of running the iron for this time.

cost = ______

Explain how the earth wire and the fuse work together to make the washing machine safer.

State the name of the wire in which the fuse is connected.

Explain why the fuse is connected into this wire.

State the name of each of these wires.

1. ______
2. ______

Suggest why the hair-dryer does not need an earth wire.

State how the fuse protects the wires in the hairdryer.

Calculate the current in the hairdryer.

Suggest a suitable current rating for the fuse.

The hairdryer does not contain an earth wire to connect to the plug.

State the feature of the hairdryer which ensures that it is safe to use without an earth wire.

the total power supplied,

power = ______

the total number of kilowatt-hours (kWh) of energy supplied to the circuit in $3.0\ \text{hours}$,

number of $\text{kW\,h}$ = ______

the current in each lamp.

current = ______

Explain why the switches are placed in the live wire and not in the neutral wire.

State the purpose of the live wire.

Explain why the neutral wire is needed.

An electrical appliance is switched on and the current in the fuse becomes greater than the rating of the fuse.

State and explain what happens.

State and explain in which of the three wires the fuse is located.

State the purpose of the neutral wire.

The live wire in the electric heater touches the outer metal case.

Explain how the earth and the fuse together protect the user from electric shock.

The hairdryer does not have an earth wire. Explain why this hairdryer is still safe to use.

In some modern homes, circuit breakers are used instead of fuses.

Suggest one advantage of using a circuit breaker rather than a fuse.

Calculate the power of the lamp.

power = ______

Calculate the energy transformed by the lamp in 30 minutes.

energy = ______

The cost of using one kilowatt-hour (kWh) of electricity is 23 cents.

Calculate the cost of using the spotlight for 30 minutes.

cost = ______

Calculate the electric current in the heating element of the shower.

current = ______

Suggest an appropriate rating for the circuit breaker in the circuit for the shower.

______

A family uses the shower for a total time of 25 minutes every day. The cost of $1\ \text{kW h}$ of electrical energy is 21 cents.

Calculate the daily cost of using the shower.

cost = ______