Domestic Energy (WJEC GCSE Science (Double Award): Physics): Exam Questions

Energy rating labels are compulsory on most household appliances such as fridges, dishwashers, washing machines and televisions. These labels allow customers to compare appliances. In addition, the labels give other information about the appliances such as how noisy they are.

Labels used to rate appliances are from A, the most efficient, to G, the least efficient.

As manufacturers have designed more efficient devices, new categories, e.g. A+, A++ and A+++ have been added to the labels.

The energy rating labels of four televisions are given below and opposite.

Information on the cost of each television is given below.

Use the information from the labels and the table to tick (✓) the three correct statements below.

Television 1 uses less energy per second than television 2

The largest televisions always use the most energy

The purchase cost of television 2 is 1.5 times that of television 3

More expensive televisions always use less energy

Television 3 uses 40 units more per year than television 4

Televisions with the same energy rating, e.g. A+, don’t always have the same power

It is claimed that power is proportional to screen size. Use the data for television 1 and television 2 to determine if this claim is true.

(i) Use the equation:

and data from the energy label to calculate how many hours the label suggests that television 2 is used for in 1 year.

[2]

Hours used = ..........

(ii) Use an equation to calculate the cost of using television 2 for 1 year if 1 unit (kWh) of electricity costs 16 p. Give your answer in pounds (£).

[2]

Cost = £ ..........

(iii) The expected lifespan of a television is 10 years. Simon concludes that it will be more cost effective to buy and run television 2 for 10 years but Sarah disagrees and claims that television 4 will be cheaper. Use the data to determine who is right.

[3]

(iv) Other than to save money, why should consumers be encouraged to choose appliances that use less energy?

[2]

The Energy Saving Trust aims to help everyone save energy every day in order to reduce the environmental damage that energy production does to the environment. It provides advice to households and businesses and gives tips for energy savings such as not leaving appliances on standby and choosing the most energy efficient appliances.

The efficiency of washing machines depends on how they are used as they can wash clothes at a variety of temperatures. Many clothes retailers and washing detergent manufacturers recommend washing clothes at 30°C in order to be more energy efficient. According to the Energy Saving Trust “Washing clothes at 30°C rather than at higher temperatures uses around 40% less energy.”

The table below gives data for different washing temperatures for a particular washing machine.

(i) Use equations to calculate the cost of washing clothes at 40°C. The cost of one unit of electricity is 16 p.

[4]

Cost = .......... p

(ii) The Energy Saving Trust suggests that washing clothes at 30°C reduces energy use by at least 40% compared to washing at higher temperatures. Use the data in the table to investigate the validity of this claim.

[3]

(iii) Washing clothes at 30°C saves money on household bills. Explain why reducing energy consumption also helps the environment.

[2]

The washing machine is connected to the ring main shown below. The voltage in the ring main is 230 V.

(i) State which wire the fuse must be connected to.

[1]

(ii) Describe the function of the earth wire.

[2]

When the voltage is 230 V, the mean power of the washing machine during a wash is 500 W. However when heating the water it must be able to produce a maximum power of 2 400 W. The householder has 3 A, 5 A and 13 A fuses available and chooses to fit a 3 A fuse into the plug. Investigate whether or not this is a suitable choice.

Domestic electricity in the UK is supplied to houses at a voltage of 230 V.

It is an alternating current (a.c.) supply.

Tick (✓) the box below the diagram which shows the voltage from an a.c. supply.

(i) To use electricity safely in the home, some safety features are used.

Draw a line to match the safety feature in the list on the left with its action on the right. Each action should only be selected once.

[3]

(ii) One purpose of safety features is to prevent fires.

State one other purpose of safety features.

[1]

A power station produces 1 200 MW at a voltage of 50 kV. This voltage is increased to 400 kV by a step-up transformer before being transmitted by the National Grid. Use an equation from page 2 to calculate the current in the wires of the grid. Assume that the transformer is 100% efficient.

Current = .......... A

The diagram shows a common domestic ring main circuit.

Give two advantages of having a ring main circuit in a house.

(i) State the function of the live wire.

[1]

(ii) Describe the function of the earth wire.

[2]

The following information is printed on the bottom of a domestic kettle:

(i) State the differences between alternating current (a.c.) and direct current (d.c.).

[2]

(ii) The voltage of the mains electricity supply in the U.K. is 230 V. Use equations and information on the kettle to calculate the resistance of the kettle heater.

[4]

Resistance = .......... Ω

The hairdryer is used to blow hot air. The current supplied is 6 A and the mains voltage is 230 V.

(i) Use the equation:

to calculate the power of the hairdryer.

[2]

power = .......... W

(ii) The following fuses are available.

Tick (✓) the box to show the correct fuse that should be used for the hairdryer.

[1]

(iii) Complete the following sentence by underlining the correct phrase in the brackets.

[2]

Fuses switch off circuits if the (current is too high / voltage is too high / power is too low) to prevent (electric shocks / wires overheating / power cuts).

A different hairdryer is now used. The power of this hairdryer is 1.5 kW.

(i) Use the equation:

to calculate the units used (kWh) by this hairdryer in 2 hours.

[2]

units used = .......... kWh

(ii) The cost per unit of electrical energy is 30 p.

Use your answer to part (c)(i) and the equation:

to calculate the cost of using this hairdryer for 2 hours.

[2]

cost = .......... p

(iii) State the cost of using this hairdryer for double the time.

[1]

cost = .......... p

(iv) Tick (✓) the box that correctly shows the power of the 1.5 kW hairdryer in watts (W).

[1]

1 500 000 W

1 500 W

1.5 W

0.015 W

A dairy farm was using 15 000 kWh of electricity every month from the National Grid.

The cost of electricity to the farm was 20 p per unit.

The farmer decided to spend £152 400 on a biogas generator which uses cow dung to generate electricity.

When working at maximum output, it was expected to reduce his demand on the National Grid to only 3 000 kWh a month.

(i) Use an equation (Use cost = units used × cost per unit) to calculate the expected monthly savings in £.

[3]

Savings = £ ..........

(ii) Calculate the payback time for the biogas generator.

[1]

Payback time = .......... months

In 2015, a householder paid £780 for electricity and £950 for gas. On 1 January 2016 solar panels were installed on the roof to provide hot water for the house. The cost of the solar panels was £4 680. In 2016, the householder paid £830 for electricity and £840 for gas.

(i) Gas was used to heat the water in the house in 2015. State how the figures allow you to come to this conclusion.

[1]

(ii) Calculate the expected payback time to recover the cost of the solar panels.

[2]

Payback time = .......... years

(iii) Explain how an increase in the cost of a unit of electricity and a unit of gas would affect the payback time.

[3]

During the two years, the cost of a unit of electricity did not change but the number of extra units of electricity used in 2016 was 300 kWh. Use an equation to calculate the cost of a unit of electricity (in pence) during 2015–2016.

Cost of unit = .......... p

A ring main is used to connect sockets to the fuse box.

The cables include live, neutral and Earth wires.

The fuse box includes miniature circuit breakers (mcb) and residual current circuit breakers (rccb).

Describe the function of each of the following wires.

live:.......................................................

neutral:........................................................

Earth:.................................................................

Explain the differences between an mcb and an rccb.

The Government intends to phase out the use of petrol and diesel cars by 2040 and switch to electric vehicles. Two such electric vehicles are the Voltsa and the Ampra. The Voltsa has an electric motor only. The Ampra has both an electric motor and a petrol engine. The table gives information about these electric vehicles and a petrol only car.

Use the information in the table to answer the following questions.

Use the information in the table to answer the following questions.

(i) Eric travels 110 km each day. He is concerned about his carbon footprint. Why would he choose a Voltsa rather than an Ampra?

[1]

(ii) Calculate the mass of CO₂ produced if the Ampra is driven 250 km.

[2]

Mass of CO₂ = .......... g

(i) The Voltsa can be charged fully in six hours using a 4 kW charger. When 1 kWh of electricity is generated it produces 0.4 kg of carbon dioxide. Calculate how much CO₂ is produced to fully charge the Voltsa.

[2]

Mass of CO₂ = .......... kg

(ii) Ian says that the CO₂ data for the Voltsa is misleading. Explain why.

[2]

Ian drives 600 km every week. He says he is not going to buy the more expensive Voltsa since it will not save him money to run compared to his petrol only car. Explain whether you agree with Ian.

The table gives information about two kettles.

(i) Calculate the units used (kWh) by kettle B if it is used to boil 0.5 litres of water 6 times a day.

[2]

units used =.............................kWh

(ii) Kettle B is used 6 times a day.

Calculate the cost of using kettle B for one week.

Cost of 1 unit = 34p.

[2]

cost =.............................p

(iii) James suggests that it would be cheaper to use kettle B because it has a lower power.

Sophia disagrees and suggests it would make no difference.

Explain who is correct.

[2]

Kettle B is connected into a ring main circuit.

A diagram of a ring main circuit is shown below.

(i) State two advantages of a ring main circuit

[2]

(ii) The ring main is protected by an mcb.

State two advantages of an mcb compared to a fuse.

[2]

(iii) The mcb has a rating of 32 A.

The maximum power that the ring main can supply is 7360 W.

The table shows some appliances in a kitchen.

Jack states that all these appliances can be connected to the ring main and used at the same time.

Determine whether Jack is correct.

[1]

A washing machine uses 0.54 kWh per wash cycle.

A customer uses it for 200 wash cycles per year.

Use the equation:

cost = units used (kWh) cost per unit

to calculate the cost of using the washing machine for 1 year in £.

The cost of a unit is £0.30.

cost = £ ..........

The wash cycle lasts for a time of 4 hours.

Use the information above and the equation:

to calculate the mean power of the washing machine during one wash cycle.

mean power = .......... kW

A biogas generator converts cow dung into biogas which can be burned to generate electricity.

A farmer buys 3 750 kWh of electricity per week from the National Grid.

He plans to buy a biogas generator which should reduce this to 750 kWh per week.

(i) Calculate how many units of electricity he would save per week.

[1]

Units saved = .......... kWh

(ii) Use the equation:

saving per week = units saved × cost per unit

to calculate the saving per week. One unit of electricity costs £0.20.

[2]

Saving per week = £ ..........

(iii) The biogas generator costs £150 000.

I. Use the equation:

payback time =

to calculate the expected payback time in weeks.

[1]

Payback time = .......... weeks

II. Calculate the expected payback time in years. 1 year = 52 weeks.

[1]

Payback time = .......... years

The diagram shows an electric hand drier connected to a 230 V a.c. mains supply.

Complete the following sentence by underlining the correct phrase.

An a.c. or alternating current (continuously changes direction / continuously changes frequency / continuously changes speed).

The electric hand drier has a label attached to it.

(i) Each time the hand drier is used it blows out hot air for 15 seconds. Use an equation from page 2 to calculate the energy transferred by the hand drier if it is used 6 times.

[3]

Energy transferred = .......... J

(ii) Use the equation:

to calculate the current when the hand drier is used.

[2]

Current = .......... A

(iii) The hand drier is connected to the mains with a standard three-core cable. Complete the table below with the value of the current in each wire in the connecting cable when the hand drier is operating normally.

[2]

A fault develops and the live wire touches the metal case of the hand drier. Explain how a residual current circuit breaker (rccb) protects the user.

A salesperson for a replacement hand drier claims it will use fewer units of electricity each time it is used because its power is 1 300 W. When it operates it blows hot air for double the time. Explain if you agree with the claim of the salesperson.