Electricity：練習題

Two resistors are connected in series. Resistor A has a resistance of \( 15 \text{ } \Omega \). If the total resistance of the circuit is \( 40 \text{ } \Omega \) and the potential difference across the power supply is \( 12 \text{ V} \), calculate the potential difference across Resistor B.

An electrical resistor has a resistance of \( 5 \text{ } \Omega \). When it is in use, it has a power output of \( 80 \text{ W} \).

Calculate the current flowing through the resistor.
Use the equation: \( \text{power} = (\text{current})^2 \times \text{resistance} \)

A current of \( 0.4 \text{ A} \) flows through a bulb for \( 30 \text{ seconds} \).
Calculate the charge flow through the bulb.

Explain why step-up transformers are used in the National Grid between power stations and transmission cables.

A resistor has a potential difference of \( 6.0 \text{ V} \) across it and transfers \( 180 \text{ J} \) of energy in \( 1 \text{ minute} \).
Calculate the resistance of the resistor.

Household appliances in the UK are connected to the mains electricity supply using three-core cables.

a) State the color of the insulation used for the following wires:
i) The live wire.
ii) The earth wire.

b) The UK mains electricity supply has a potential difference of \( 230 \text{ V} \). Calculate the energy transferred to a device when a total charge of \( 30 \text{ C} \) flows through it.
Use the equation: \( \text{energy transferred} = \text{charge flow} \times \text{potential difference} \)