Social networks

OpenProf

Unlock access to content

Select one option:

Free of charge

Unlock the chapter "Electrical Energy "

Unlock access to the solution of problems in this chapter.
Free of charge Price: 3.00 £

Continue »

Subscribe to OpenProf If you do not get a better grade, you get your money back!

Unlock access to all problems solutions.
Available from 8.25 £ / month.

Continue »

physics Physics For High Schools (KS4)

Solved problems for the chapter:

Electrical Energy

View the theory »

Electric Power for A-Levels

1. Electrical work

2. Electrical power

3. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:electrical_energy/3636/

Example 1.

An energy-saving light bulb is connected to a 220 V source. Calculate how much electrical energy it consumes in 20 minutes if a current of 0.1 A flows through it.

Example 2.

A wire with an internal resistance of is connected to a voltage of 220 V. Calculate in what time it emits 4.0 kW h of heat energy.

Calculate the amount of energy released in a lightning strike if the current at impact is about 15 kA, the voltage is 10 MV and the duration of the impact is approximately 1 ms.

A heater with a resistance of is connected to a 220 V voltage source. If the cost of running the heater is € 0.05 per kilowatt-hour, calculate the cost of running the heater for 8 hours.

Determine whether the following statements are correct:

Electrical work depends on the flow of electric charge and voltage.
The basic unit for electrical work is the kilowatt hour.
With electrical work, there can be change in the energy of a body.
Energy conversion in electricity is always accompanied by heat.
In electric motors, all electrical work is converted into mechanical work.
When electric current flows through a resistor, all the electrical work done on the resistor is converted into heat. So, it heats up.
In filament lamps, most of the electrical part is converted to light.

A 6 V battery having an electrical charge of 2000 mA h is connected to a light bulb. How much electrical work is done by the battery to lit the light bulb before it is discharged?

A household with a mains voltage of 220 V consumes 400 kW hr of electricity per month. What is the average electric current used in the house? (Assume the month to have 30 days).

An electric current of 100 mA flows through a 100 resistor. How much electrical work is done in one minute? What does this work turn into?

An electric heater in a room is connected to a 220 V voltage source. The resistance wire of the heater has a resistance of .

How much electrical energy does the heater receive in one month (30 days) if it is connected for an average of 8 hours a day?
How much heat does it emit into the room?
What is the cost of the electrical energy received by the heater if 100 MJ of electrical energy costs 1.5 EUR?

10.

Two resistors are connected to their own voltage sources. The voltage across the second resistor is three times the voltage across the first resistor and the current through the first resistor is twice the current through the second resistor. Find the ratio of the electrical energies received by both resistors at the same time.

11.

A drilling machine connected to a 230 V source consumes 4 MJ of electrical energy when used to drill for two hours. How much current flows through the drill?

12.

An electric motor provides of useful output energy. The efficiency of the motor is . How much electrical energy is supplied to the motor?

13.

A lamp rated , is switched on for . How much energy is transferred?

14.

The cost of electrical energy is for each unit of . A heater is switched on for . What is the cost of this use?

15.

A lamp rated , is switched on for one minute. How much energy is transferred by the lamp?

16.

There is a current in a resistor for a time . The potential difference (p.d.) across the resistor is . A student calculates the product . In which unit is the student’s answer measured?

ampere
coulomb
joule
watt

17.

A cell passes a current of in a circuit for . In this time the cell transfers of energy. What is the electromotive force (e.m.f.) of the cell?

18.

A circuit contains a cell of electromotive force (e.m.f.) of . The current in the circuit is . How much energy is converted by the cell in ?

19.

There is a current of in a resistor for . The potential difference (p.d.) across the resistor is . How much energy is transferred in the resistor?

20.

The diagram shows part of an electric circuit. The reading on the voltmeter is . The current in

the resistor is .

One coulomb of charge flows from P to Q through the resistor. How much energy is transferred in the resistor?

21.

An electrical heater transfers thermal energy to the surroundings. The graph shows how the amount of thermal energy transferred varies with time.

The heater continues to transfer energy at the same rate. How much thermal energy is transferred by the heater in ?

22.

A water heater is connected to a supply and there is a current of in the heater. It takes to heat the water to the required temperature. How much energy is supplied by the heater?

23.

An electricity meter records that of electrical energy are drawn from the mains supply in a period. What is the average rate of electrical charge passing through the meter?

24.

A battery is connected to a circuit. It is switched on for . During that time, there is a current of in the circuit and the battery supplies a total of of energy. Which row gives the charge that passes and the electromotive force (e.m.f.) of the battery?