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Conservation and dissipation of energy - High demand – Questions

Q1.All European Union countries are expected to generate 20% of their electricity using renewable energy sources by 2020.

The estimated cost of generating electricity in the year 2020 using different energy sources is shown in Table 1.

Table 1

Energy source Estimated cost (in the year 2020) in pence per kWh

Nuclear 7.8

Solar 25.3

Tidal 18.8

Wind 10.0

France generated 542 billion kWh of electricity using nuclear power stations in 2011.France used 478 billion kWh of electricity and sold the rest of the electricity to other countries in 2011.

(a) France may continue generating large amounts of electricity using nuclear power stations instead of using renewable energy resources.

Suggest two reasons why.

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2. _________________________________________________________________

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(b) Give two disadvantages of generating electricity using nuclear power stations.

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(c) A panel of solar cells has an efficiency of 0.15.

The total power input to the panel of solar cells is 3.2 kW.

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Calculate the useful power output of this panel of solar cells in kW.

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Useful power output = _______________ kW(2)

(d) Table 2 shows the manufacturing cost and efficiency of different types of panels of solar cells.

Table 2

Type of Solar Panel Cost to manufacture a 1 m2 solar panel in £ Efficiency in %

A 40.00 20

B 22.50 15

C 5.00 10

Some scientists think that having a low manufacturing cost is more important than improving the efficiency of solar cells.

Use information from Table 2 to suggest why.

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(Total 8 marks)

Q2.The figure below shows a rollercoaster.

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The rollercoaster car is raised a vertical distance of 35 m to point A by a motor in 45 seconds.

The mass of the rollercoaster is 600 kg.

The motor has a power rating of 8 000 W.

(a) Calculate the percentage efficiency of the motor.

Gravitational field strength = 9.8 N / kg.

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Efficiency = __________________ %(5)

(b) The rollercoaster rolls from point A to point B, a drop of 35 m.

Calculate the speed of the roller coaster at point B.

Assume that the decrease in potential energy store is equal to the increase in kinetic energy store.

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Speed at point B = __________________ m / s(6)

(Total 11 marks)

Q3.The figure below shows a cool box.

A cool box is used to keep food colder than the surroundings. The cool box consists of plastic walls with a layer of polyurethane foam between them.

(a) The polyurethane foam has a low U-value.

Why does the polyurethane foam need to have a low U-value?

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(b) The polyurethane foam contains air bubbles.

Explain how the air bubbles reduce energy transfer through the walls of the cool box.

You should refer to the processes of energy transfer in your answer.

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(c) An ice-pack can be placed inside the cool box. An ice-pack contains a material with a very high specific heat capacity. The ice-pack is frozen in a freezer and cooled to –18 °C before being put in the cool box.

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The ice-pack keeps the contents of the cool box cooler than the surroundings for a long time.

Describe how.

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(Total 7 marks)

Q4.Table 1 shows information about different light bulbs.

The bulbs all have the same brightness.

Table 1

Type of bulb Input power in watts Efficiency

Halogen 40 0.15

Compact fluorescent (CFL)

14 0.42

LED 7 0.85

(a) (i) Calculate the useful power output of the CFL bulb.

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Useful power output = _______________ watts(2)

(ii) Use your answer to part (i) to calculate the waste energy produced each second by a CFL bulb.

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Waste energy per second = _______________ joules

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(1)

(b) (i) A growth cabinet is used to investigate the effect of light on the rate of growth of plants.

The figure below shows a growth cabinet.

In the cabinet the factors that affect growth can be controlled.

A cooler unit is used to keep the temperature in the cabinet constant. The cooler unit is programmed to operate when the temperature rises above 20 °C.

The growth cabinet is lit using 50 halogen bulbs.

Changing from using halogen bulbs to LED bulbs would reduce the cost of running the growth cabinet.

Explain why.

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(ii) A scientist measured the rate of growth of plants for different intensities of light.

What type of graph should be drawn to present the results?

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Give a reason for your answer.

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(c) Table 2 gives further information about both a halogen bulb and a LED bulb.

Table 2

Type of bulb

Cost to buy

Lifetime in hours

Operating cost over the lifetime of one bulb

Halogen £1.50 2 000 £16.00

LED £30.00 48 000 £67.20

A householder needs to replace a broken halogen light bulb.

Compare the cost efficiency of buying and using halogen bulbs rather than a LED bulb over a time span of 48 000 hours of use.

Your comparison must include calculations.

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(Total 12 marks)

Q5.(a) The table gives information about some ways of reducing the energy consumption in

a house.

Method of reducing energy consumption

Installation cost in £

Annual saving on energy bills in £

Fit a new hot water boiler 1800 200

Fit a solar water heater 2400 100

Fit under floor heating 600 50

Fit thermostatic radiator valves 75 20

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Which way of reducing energy consumption is most cost effective over a 10-year period?

To obtain full marks you must support your answer with calculations.

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(b) Explain why using an energy-efficient light bulb instead of an ordinary light bulb reduces the amount of carbon dioxide emitted into the atmosphere.

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(Total 5 marks)

Q6.(a) Solar energy is a renewable energy source used to generate electricity.

(i) What is meant by an energy source being renewable?

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(ii) Name two other renewable energy sources used to generate electricity.

1. ____________________________________________________________

2. ____________________________________________________________(1)

(b) A householder uses panels of solar cells to generate electricity for his home.The solar cells are tilted to receive the maximum energy input from the Sun.

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The data in the table gives the average energy input each second (in J/s), to a 1 m2 area of solar cells for different angles of tilt and different months of the year.

MonthAngle of tilt

20° 30° 40° 50°

February 460 500 480 440

April 600 620 610 600

June 710 720 680 640

August 640 660 640 580

October 480 520 500 460

December 400 440 420 410

(i) Use the data in the table to describe how the average energy input to the solar cells depends on the angle of tilt.

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(ii) The total area of the solar cell panels used by the householder is 5 m2.

The efficiency of the solar cells is 0.18.

Calculate the average maximum electrical energy available from the solar cell panels each second in June.

Show clearly how you work out your answer.

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Maximum energy = ________________________ joules/second(3)

(c) The diagram shows part of the National Grid.

(i) Even though the householder uses solar cells to generate electricity for his home, the home stays connected to the National Grid.

Give one reason why the householder should stay connected to the National Grid.

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(ii) The step-up transformer increases the efficiency of the National Grid.

Explain how.

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(Total 10 marks)

Q7.(a) The diagram shows how much heat is lost each second from different parts of an

uninsulated house.

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(i) Each year, the house costs £760 to heat.

How much money is being wasted because of heat lost through the roof?


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(ii) Insulating the loft would cut the heat lost through the roof by 50 %.

The loft insulation has a payback time of years.

How much did the loft insulation cost to buy?

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Cost of loft insulation = £ _________________________(1)

(b) What happens to the wasted energy?

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(Total 4 marks)

Q8.The farmers in a village in India use solar powered water pumps to irrigate the fields.

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On average, a one square metre panel of solar cells receives 5 kWh of energy from the Sun each day.The solar cells have an efficiency of 0.15

(a) (i) Calculate the electrical energy available from a one square metre panel of solar cells.


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Electrical energy = __________________________ kWh(2)

(ii) On average, each solar water pump uses 1.5 kWh of energy each day.

Calculate the area of solar cells required by one solar water pump.

Area = _____________________________ square metres(1)

(b) Give one reason why the area of solar cells needed will probably be greater than the answer to part (a)(ii).

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(Total 4 marks)

Q9.A homeowner had a new gas boiler installed.

(a) The following information is an extract from the information booklet supplied with the boiler.

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Fuel Natural Gas

Water temperature 60 °C

Energy supplied to gas boiler 8.0 kJ/s (8.0 kW)

Efficiency 0.95

(i) Calculate the energy transferred each second by the gas boiler to the water inside the boiler.


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Energy transferred by the gas boiler each second = ___________ kJ(2)

(ii) The energy value of the gas used in a home is measured in kilowatt-hours (kWh).

The homeowner has a pre-payment meter and pays £30 into his account. With a pre-payment meter, gas costs 15p per kilowatt-hour.

Calculate the total number of hours that the gas boiler would operate for £30.


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Number of hours = _________________________(2)

(b) Although the gas boiler is very efficient, some energy is wasted.

Explain what happens to the waste energy.

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(Total 6 marks)

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Q10.The diagram shows a small-scale, micro-hydroelectricity generator which uses the energy of falling river water to generate electricity. The water causes a device, called an Archimedean screw, to rotate.The Archimedean screw is linked to the generator by a gearbox.

(a) Each second, the micro-hydroelectricity generator transforms 80 000 joules of gravitational potential energy into 60 000 joules of electrical energy.

(i) Fill in the missing word to complete the energy transformation diagram.

Gravitational potentialenergy of the falling water

________________ energy

of the Archimedean screw

Electrical energygenerated

(1)

(ii) Use the equation in the box to calculate the efficiency of the micro-hydroelectricity generator.


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Efficiency = ______________________________(2)

(b) The power output from a conventional large-scale hydroelectric power station is 100 000 times more than the power output from a micro-hydroelectric system.

Give one disadvantage of a conventional large-scale hydroelectric power station compared to the micro-hydroelectric system.

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(c) The electricity generated by a micro-hydroelectric system is transferred via a transformer directly to local homes. The electricity generated by a conventional large-scale hydroelectric power station is transferred to the National Grid, which distributes the electricity to homes anywhere in the country.

(i) What is the National Grid?

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(ii) Explain why transferring the electricity directly to local homes is more efficient than using the National Grid to distribute the electricity.

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(Total 7 marks)

Q11.The table gives data about two types of low energy bulb.

Type of bulb Power inputin watts

Efficiency Lifetimein hours

Cost ofone bulb

Compact FluorescentLamp (CFL) 8 20% 10 000 £3.10

Light Emitting Diode(LED) 5 50 000 £29.85

(a) Both types of bulb produce the same useful power output.

(i) Calculate the useful power output of the CFL.


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Useful power output = _________________________ W

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(2)

(ii) Calculate the efficiency of the LED bulb.


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Efficiency = ___________________________(1)

(b) LED bulbs are expensive. This is because of the large number of individual electronic LED chips needed to produce sufficient light from each bulb.

(i) Use the data in the table to evaluate the cost-effectiveness of an LED bulb compared to a CFL.

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(ii) Scientists are developing brighter and more efficient LED chips than those currently used in LED bulbs.

Suggest one benefit of developing brighter and more efficient LED chips.

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(Total 6 marks)

Q12.(a) The diagram shows a solar powered device being used to recharge a mobile phone.

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On average, the solar cells produce 0.6 joules of electrical energy each second.The solar cells have an efficiency of 0.15.

(i) Calculate the average energy input each second to the device.


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Average energy input each second = __________________ J/s(2)

(ii) Draw a labelled Sankey diagram for the solar cells.The diagram does not need to be drawn to scale.

(1)

(b) Scientists have developed a new type of solar cell with an efficiency of over 40 %.The efficiency of the solar cell was confirmed independently by other scientists.

Suggest why it was important to confirm the efficiency independently.

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(c) The electricity used in homes in the UK is normally generated in a fossil fuel power station.

Outline some of the advantages of using solar cells to generate this electricity.

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(Total 6 marks)

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