Safe electricals

Question 1

What device changes resistance?

Answer 1

A variable resistor, or rheostat changes the resistance. Longer lengths of wire have more resistance; thinner wires have more resistance.

Question 2

Voltage

Answer 2

• Voltage (potential difference) is measured in volts (V) using a voltmeter connected in parallel.
  
  • For a fixed resistor, as the voltage across it increases, the current increases.
  • For a fixed power supply, as resistance increases, the current decreases.

Question 3

Resistance Eq.

Answer 3

resistance = voltage/current

Question 4

Voltage Eq.

Answer 4

voltage = resistance x current

Question 5

Current Eq.

Answer 5

current = voltage/resistance

Question 6

All types of wires

Answer 6

• The live wire carries a high voltage around the house.
• The neutral wire completes the circuit, providing a returns path for the current.
• The earth wire is connected to the case of an appliance to prevent it becoming live.

Question 7

Double insulated

Answer 7

Double insulated appliances do not need an earth wire as the outer case is not a conductor.

Question 8

What does a fuse contain?

Answer 8

• A fuse contains wire which melts, breaking the circuit, if the current becomes too large.
• No current can flow, preventing overheating and further damage to the appliance.
• A re-settable fuse (circuit-breaker) doesn’t need to be replaced to restore power; it can be re-set.

Question 9

What does the earth wire and fuse stop?

Answer 9

• Earth wires and fuses stop a person receiving an electric shock if they touch a faulty appliance.
• As soon as the case becomes ‘live’, a large current Flows In the Earth and live wires and the fuse ‘blows’.

Question 10

Power Eq.

Answer 10

power = voltage x current