Electricity：練習問題

Electric current in a solid metallic conductor is best described as a flow of which of the following?

An electric kettle is connected to a \(230\text{ V}\) mains supply. If the current flowing through the heating element is \(8.0\text{ A}\), what is the power rating of the kettle?

An electric room heater is rated at \( 2.5\text{ kW} \) and is connected to a \( 230\text{ V} \) mains supply. Which of the following standard fuses is most appropriate for the plug of this heater?

Which of the following is the correct unit for measuring electric charge?

A simple series circuit consists of a \( 9.0\text{ V} \) battery and two resistors connected in series. The resistors have resistances of \( 5.0\text{ }\Omega \) and \( 10.0\text{ }\Omega \) respectively. Calculate the current flowing through the circuit.

A rechargeable battery is labeled with a capacity of \(2500\text{ mAh}\). Calculate the total charge, in coulombs, that this battery can deliver if it provides a steady current of \(0.5\text{ A}\) until it is fully discharged.

A circuit contains a \(12\text{ V}\) d.c. supply, a \(400\text{ }\Omega\) fixed resistor, and a thermistor connected in series. At room temperature, the thermistor resistance is \(200\text{ }\Omega\). Calculate the voltage across the fixed resistor and explain how this voltage changes when the temperature of the thermistor increases.

An electric heater is connected to a \(230\text{ V}\) supply. If \(4600\text{ C}\) of charge passes through the heater in \(5.0\text{ minutes}\), calculate the power rating of the heater in kilowatts.

An electric kettle is used to boil water. The kettle is connected to a \(230\text{ V}\) mains supply and has a power rating of \(2.3\text{ kW}\).

(a) Calculate the current in the kettle and select the most appropriate fuse from the following list: \(3\text{ A}\), \(5\text{ A}\), or \(13\text{ A}\).
(b) The kettle is switched on for \(3\text{ minutes}\). Calculate the total energy, in joules, transferred by the kettle during this time.
(c) Calculate the total charge, in coulombs, that flows through the heating element during these \(3\text{ minutes}\).
(d) The heating element is a resistor. Explain why its temperature increases when an electric current flows through it.

A student builds a circuit with a \(24\text{ V}\) d.c. power supply and three resistors. Resistor A (\(10\text{ Ω}\)) is connected in series with a parallel combination of Resistor B (\(20\text{ Ω}\)) and Resistor C (\(20\text{ Ω}\)).

(a) Calculate the total resistance of the circuit.
(b) Calculate the total current flowing from the power supply.
(c) Calculate the power dissipated by Resistor A.