Sec 4 Physics Practical Electricity topical questions

State what is meant by the heating effect of an electric current, and name one appliance that uses it deliberately.

Name the three wires in a mains cable, state the insulation colour of each, and state which one normally carries no current.

A lamp draws 0.25 A from a 230 V supply. Calculate its power.

State why the fuse and the switch are both connected in the live wire.

Calculate the energy used by a 2.0 kW fan heater in 3.0 hours, in kW h.

A 2300 W kettle operates on a 230 V supply.

1. (a)Calculate the current it draws.[2]
2. (b)Select a suitable fuse from 3 A, 5 A, 13 A and explain the choice.[2]
3. (c)Explain why a 30 A fuse would be a poor choice.[2]

The electricity tariff is 30 cents per kW h. A household runs a 200 W television for 4.0 hours and a 1.2 kW rice cooker for 20 minutes daily.

1. (a)Calculate the daily energy used in kW h.[3]
2. (b)Calculate the daily cost.[1]
3. (c)State which appliance costs more per hour to run and why.[2]

A metal toaster is earthed and fused at 13 A; it draws 5.0 A normally.

1. (a)Explain what happens electrically if the live wire touches the metal casing.[3]
2. (b)Explain why the person touching the toaster at that moment is protected.[2]
3. (c)State what changes if the toaster has a plastic (double-insulated) case.[1]

A student rewires a plug: brown wire to the earth terminal, blue wire to the fused live terminal, green-and-yellow wire left unconnected.

1. (a)Identify each error.[2]
2. (b)State the danger if this plug is used.[3]
3. (c)Describe the correct wiring.[1]

A household circuit is protected by a 20 A circuit breaker. The wiring in the walls is rated to carry 20 A safely. A resident plugs a 2.0 kW heater, a 1.5 kW kettle and a 1.0 kW iron into one 4-way extension lead (rated 13 A) on that circuit, all running at once on a 230 V supply.

1. (a)Calculate the total current the three appliances draw.[3]
2. (b)Explain whether the circuit breaker operates.[2]
3. (c)Explain why the extension lead is the component at risk and what could happen to it.[3]

A bathroom uses a hair dryer (1.2 kW, 230 V) near a sink. A resident with wet hands picks up the dryer by its cracked plastic handle while standing on a wet floor.

1. (a)Calculate the normal operating current of the dryer.[2]
2. (b)Explain two ways the situation increases the risk of a serious shock compared with dry conditions.[4]
3. (c)State two practices that would reduce the risk.[2]

An office desk has a laptop (65 W), two monitors (40 W each) and a desk lamp (12 W) on one double socket via a 13 A extension block, plus a 2.0 kW room heater plugged directly into the wall socket beside it. Supply is 230 V.

1. (a)Calculate the current through the extension block.[2]
2. (b)Explain why this arrangement is acceptable while plugging the heater into the block would not be.[4]
3. (c)The heater’s plug fuse is rated 13 A. Verify this is sensible.[2]

A country uses 230 V mains. A visitor brings a 1200 W appliance designed for 120 V mains.

1. (a)Assuming its resistance is unchanged, calculate the current it would draw on 230 V.[3]
2. (b)Calculate the power it would convert on 230 V and state the likely consequence.[3]
3. (c)State what a travel adapter does and does not do about this problem.[2]