Exampro GCSE Physics P Foundation - Electrical Energy and Efficiency Self Study Questions Name: Class: Author: Date: Time: 76 Marks: 76 Comments: Page of 3
Q. The figure below shows a car with an electric motor. The car is moving along a flat road. (a) (i) Use the correct answers from the box to complete each sentence. light electrical kinetic potential sound The car s motor transfers... energy into useful... energy as the car moves. Some energy is wasted as... energy. (3) What happens to the wasted energy? () (b) The electric motor has an input energy of 50 000 joules each second. The motor transfers 35 000 joules of useful energy each second. Calculate the efficiency of the electric motor. Use the correct equation from the Physics Equations Sheet. Efficiency =... (Total 6 marks) Page 2 of 3
Q2. The Sankey diagrams show the energy transfers in a traditional coal-burning power station and a combined heat and power (CHP) station. Waste energy Waste energy (a) What effect does the waste energy from a power station have on the surroundings? () (b) Calculate the efficiency of the CHP station. Use the correct equation from the Physics Equations Sheet. Efficiency =... (c) Why is a CHP station more efficient than a traditional coal-burning power station? Page 3 of 3
(d) A CHP station is usually used to meet the demand for electricity within the local area. The electricity is not transmitted and distributed through the National Grid. (i) What is the National Grid? Tick ( ) one box. A system of cables and pylons. A system of cables and transformers. A system of cables, transformers and power stations () Using the electricity locally and not transmitting it through the National Grid increases the overall efficiency of a CHP station by 7%. Give one reason why. () (Total 7 marks) Q3. The pictures show six different household appliances. (a) Four of the appliances, including the fan heater, are designed to transform electrical energy into heat. Name the other three appliances designed to transform electrical energy into heat. 2 3 (3) Page 4 of 3
(b) The bar chart shows the power of three electric kettles, X, Y and Z. Kettle (i) In one week, each kettle is used for a total of 30 minutes. Which kettle costs the most to use? Put a tick ( ) next to your answer. X Y Y () A new express boil kettle boils water faster than any other kettle. Draw a fourth bar on the chart to show the possible power of an express boil kettle. () Page 5 of 3
(c) The graph shows how the time to boil water in an electric kettle depends on the volume of water in the kettle. Volume of water in litres A householder always fills the electric kettle to the top, even when only enough boiling water for one small cup of coffee is wanted. Explain how the householder is wasting money. (3) (Total 8 marks) Page 6 of 3
Q4. The picture shows a washing machine. When the door is closed and the machine switched on, an electric motor rotates the drum and washing. (a) Complete the following sentences. (i) An electric motor is designed to transform electrical energy into... energy. () Some of the electrical energy supplied to the motor is wasted as... energy and... energy. () (b) What happens to the energy wasted by the electric motor? () Page 7 of 3
(c) The graph shows that washing clothes at a lower temperature uses less energy than washing them at a higher temperature. Using less energy will save money. Temperature setting in C (i) Electricity costs 5p per kilowatt-hour (kwh). The temperature setting is turned down from 40 C to 30 C. Use the graph and equation in the box to calculate the money saved each wash cycle. total cost = number of kilowatt-hours x cost per kilowatt-hour Show clearly how you work out your answer. Money saved =... Reducing the amount of energy used by washing machines could reduce the amount of carbon dioxide emitted into the atmosphere. Explain why. (Total 7 marks) Page 8 of 3
Q5. (a) The Sankey diagram for a low energy light bulb, known as a CFL, is shown below. (i) What is the useful energy output that the CFL is designed to produce? () What effect does the waste energy output have on the surrounding air? () (iii) Use the information in the diagram to calculate the efficiency of the CFL. Use the correct equation from the Physics Equations Sheet. Show clearly how you work out your answer. Efficiency =... Page 9 of 3
(iv) CFLs contain mercury. Mercury is a poisonous substance. It is important that old CFLs are sent for recycling and not thrown into a rubbish bin. Suggest one reason why. () (b) A new type of low energy bulb uses light emitting diodes (LEDs). Draw a ring around the correct answer in the box to complete the sentence. LED bulbs are more efficient than CFLs. This means that LED bulbs a smaller waste the same proportion of the input energy compared to CFLs. a bigger () (c) The graph shows how the outside surface temperatures of a CFL and an LED bulb change after they are switched on. Apart from a higher efficiency, suggest one advantage of using an LED bulb rather than a CFL. () Page 0 of 3
(d) At the moment, LED bulbs are much more expensive to buy than CFLs. Which two of the following would a homeowner need to know to decide whether it would be cost-effective to replace a CFL with an equally bright LED bulb? Tick ( ) two box. The number of hours each bulb lasts before needing to be replaced The power of each bulb in watts The voltage of the mains electricity supply () (Total 8 marks) Q6. The picture shows a new washing machine. When the door is closed and the machine switched on, an electric motor rotates the drum and washing. (a) Complete the following sentences. (i) An electric motor is designed to transform electrical energy into... energy. () Some of the electrical energy supplied to the motor is wasted as... energy and... energy. () Page of 3
(b) What happens to the energy wasted by the electric motor? () (c) The diagram shows the label from the new washing machine. An A rated washing machine is more energy efficient than a C rated washing machine. Explain what being more energy efficient means. Page 2 of 3
(d) The graph shows that washing clothes at a lower temperature uses less energy than washing them at a higher temperature. Using less energy will save money. (i) Electricity costs 2 p per kilowatt-hour (kwh). The temperature setting is turned down from 40 C to 30 C. Use the graph and equation in the box to calculate the money saved each wash cycle. total cost = number of kilowatt-hours cost per kilowatt-hour Show clearly how you work out your answer. Money saved =... p Suggest why reducing the amount of energy used by washing machines could reduce the amount of carbon dioxide emitted into the atmosphere. () (Total 8 marks) Page 3 of 3
Q7. (a) The diagram shows the energy transformations produced by a television. When the television is working, 200 joules of energy are supplied to the television every second. The useful energy transferred by the television is 720 joules every second. (i) Use the equation in the box to calculate the efficiency of the television. Show clearly how you work out your answer. Efficiency =... Use one word from the diagram to complete the following sentence. The electrical energy that is not usefully transformed by the television is wasted as.... () Page 4 of 3
(b) Drawn below are the Sankey diagrams for three televisions, J, K and L. The diagrams are drawn to the same scale. J K L Which one of the televisions, J, K or L, is the most efficient? Write your answer in the box. Give a reason for your answer. Page 5 of 3
(c) A homeowner is sent an electricity bill every 3 months. The total amount of electrical energy used during one 3-month period was 800 kilowatt-hours. Electrical energy costs 5p per kilowatt-hour. Use the equation in the box to calculate the cost of the energy transferred from the mains electricity supply. total cost = number of kilowatt-hours cost per kilowatt-hour Show clearly how you work out your answer and give the unit. Cost =... (Total 7 marks) Q8. The drawing shows parts of a house where it is possible to reduce the amount of energy lost. (a) Give one way in which the amount of energy lost can be reduced from each of the following parts of the house., 2 and 4... 5... 7... (3) Page 6 of 3
(b) Energy consumption can be reduced by using a more efficient boiler or more efficient light bulbs. What is meant by a more efficient light bulb?...... () (Total 4 marks) Q9. (a) The block diagram shows the important parts of a coal burning power station. Use words from the box to complete the block diagram boiler condenser furnace generator (b) The diagram shows the energy transformations in a coal burning power station. Calculate the efficiency of the power station. Write down the equation you use, and then show clearly how you work out your answer. Efficiency =... Page 7 of 3
(c) Draw a ring around the correct answer to complete the following sentence. If fewer coal burning power stations are used to generate electricity the amount of decrease. carbon dioxide emitted into the atmosphere will not change. increase. () (d) Some types of power station generate electricity by burning a biofuel. Give one example of a biofuel. () (e) Nuclear power stations generate electricity without burning a fuel. Name the process by which a nuclear fuel provides the energy needed to generate electricity. () (Total 7 marks) Q0. The diagram shows the energy transformations produced by a TV. (a) Use words from the diagram to complete the following sentence. The TV is designed to transform... energy into light and... energy. Page 8 of 3
(b) Which one of the following statements is false? Put a tick ( ) in the box next to the false statement. The energy transformed by the TV makes the surroundings warmer. The energy transformed by the TV becomes spread out. The energy transformed by the TV will be destroyed. () (c) Two different makes of television, A and B, transform energy at the same rate. Television A wastes less energy than television B. Complete the following sentence by drawing a ring around the correct line in the box. Television A has a higher efficiency than the same efficiency as a lower efficiency than television B. () (Total 4 marks) Q. (a) The drawing shows the energy transferred each second by a television set. (i) What form of energy is transferred as waste energy by the television set?.. () Page 9 of 3
What effect will the waste energy have on the air around the television set?.. () (iii) Use the following equation to calculate the efficiency of the television set. efficiency =.... Efficiency =... (b) The diagrams show the energy transferred each second for three different types of lamp. For each lamp the electrical energy input each second is 00 joules. Page 20 of 3
Which type of lamp is the most efficient?... Give a reason for your choice....... (Total 6 marks) Q2. The diagrams show what happens to each 00 joules of energy from burning coal on an open fire and in a stove. (a) Add the missing figures to the diagrams. (3) Page 2 of 3
(b) Which is more efficient, the open fire or the stove? Give a reason for your answer....... () (Total 4 marks) Page 22 of 3
M. (a) (i) electrical correct order only kinetic sound transferred into surroundings / atmosphere accept warms the surroundings allow released into the environment becomes heat or sound is insufficient (b) 0.7 / 70 % an answer of 70 without % or with the wrong unit or 0.7 with a unit gains mark 2 [6] M2. (a) warms it do not accept answers in terms of waste gases or pollution (b) 80% or 0.8 answers of 80 or 0.8 plus a unit gain mark only or allow mark for a correct substitution, ie (c) an answer of 35% or 0.35 gains mark answers of 85%, 75%, 0.85 or 0.75 gain mark some of the energy that would be wasted (by a coal-burning power station) accept less waste energy 2 is usefully used (to heat homes etc) accept energy used to heat homes etc (d) (i) A system of cables and transformers less energy / power loss / wasted (in shorter cables) accept no energy / power loss / wasted (in shorter cables) accept energy is lost when transmitted through cables do not accept electricity for energy [7] Page 23 of 3
M3. (a) iron hairdryer kettle answers can be in any order (b) (i) Y bar drawn with any height greater than Y ignore width of bar (c) (bigger volume) takes more time (to boil) accept explanation using data from graph (so) more energy transferred do not accept electricity for energy (and) this costs more money ignore reference to cost of water wasting more money because heating more water than needed is insufficient [8] M4. (a) (i) kinetic do not accept movement thermal sound accept heat for thermal do not accept noise for sound both answers required in either order (b) transferred to surroundings / surrounding molecules / atmosphere it escapes is insufficient or becomes dissipated / spread out accept warms the surroundings accept degraded / diluted accept a correct description for surroundings eg to the washing machine do not accept transformed into heat on its own Page 24 of 3
(c) (i) 3 (.0 p) allow mark for correct substitution of correct values ie 0.2 x 5 allow mark for calculating cost at 40 C (6.5p) or cost at 30 C (3.5p) 2 any two from: less electricity needed ignore answers in terms of the washing machine releasing less energy an answer in terms of the washing machine releasing CO 2 negates mark do not accept less energy is produced fewer power stations needed less fuel is burned accept a correctly named fuel do not accept less fuel is needed 2 [7] M5. (a) (i) light (energy) this answer only raises its temperature accept warms / heats it accept air molecules / particles gain energy / move faster do not accept heat do not accept pollution (iii) 20% or 0.2 allow mark for correct substitution ie subsequent step is shown provided that no 20 without % scores mark, 20 or 0.2 with a unit scores mark 2 Page 25 of 3
(iv) mercury can be recovered /reused / recycled or mercury (vapour) does not get into the atmosphere / environment / air accept to stop mercury poisoning the land / getting into the food chain / water supply accept poisonous gas for mercury (vapour) do not accept general poisoning cause harm to the environment is insufficient (b) a smaller (c) reaches full brightness faster accept brighter / switches on faster accept it does not get as hot accept it will not burn someone who touches it accept stays cool accept temperature does not increase as much accept temperature only goes to 24 ( C) accept contains no mercury do not accept wastes less energy (d) top two boxes both ticked The number of hours each bulb lasts before needing to be replaced. The power of each bulb in watts. [8] M6. (a) (i) kinetic do not accept movement thermal accept heat for thermal sound do not accept noise for sound both answers required in either order Page 26 of 3
(b) (c) transferred to surroundings / surrounding molecules / atmosphere it escapes is insufficient or becomes dissipated / spread out accept warms the surroundings accept degraded / diluted accept a correct description for surroundings eg to the washing machine do not accept transformed into heat on its own a smaller proportion / percentage of the energy supplied is wasted owtte accept a statement such as less energy is wasted for mark do not accept costs less to run ignore references to uses less energy 2 (d) (i) 2.4 (p) accept 2 p if it is clear from the working out this is rounded from 2.4 p allow mark for correct substitution of correct values ie 0.2 2 allow mark for calculating cost at 40 C (3.2 p) or cost at 30 C (0.8 p) 2 any one from: less electricity needed ignore answers in terms of the washing machine releasing less energy an answer in terms of the washing machine releasing CO 2 negates the mark do not accept less energy is produced fewer power stations needed less fuel is burned accept a correctly named fuel do not accept less fuel is needed [8] Page 27 of 3
M7. (a) (i) 0.6 or 60% an answer of 0.6 / 60 with a unit gains mark only an answer of 60 gains mark only 2 heat allow thermal (b) K reason only scores if K is chosen smallest amount of wasted energy reasons must be comparative accept waste arrow is narrowest or largest amount of useful energy accept useful arrow is widest waste arrow is smallest is insufficient (c) 2 000 p or 20 to score both marks the unit must be consistent with the numerical answer answers 2 000 and 20 gain mark only allow mark for correct substitution ie 800 5 or 800 0.5 provided no subsequent step shown 2 [7] M8. (a) insulation allow example e.g fibreglass double glazing allow curtains draught excluder allow double glazing / close fitting door allow turning down thermostat once only / turn down the heating Page 28 of 3
(b) transfers more useful energy allow converts more energy into light / less into heat / less energy wasted [4] M9. (a) boiler generator (b) 0.3 or 30% allow mark for substitution of 2 correct values taken from the Sankey diagram into correct equation 2 (c) decrease (d) any named biofuel eg wood, ethanol, straw (e) (nuclear) fission [7] M0. (a) electrical sound correct order only (b) the energy transformed by the TV will be destroyed (c) a higher efficiency than [4] Page 29 of 3
M. (a) (i) heat temperature increases or (cause) convection (currents) accept gets warmer accept gets hotter (iii) 60% or 0.6 60 without % scores mark 0.6 with a unit scores mark 60 with incorrect unit scores mark or correct substitution for mark 2 (b) street more (energy transferred as) light or less (energy transferred as) heat or useful energy output the highest can only score this mark if first mark scored all efficiencies calculated correctly score 2nd mark point [6] M2. (a) (i) 5* 60* [* if incorrect but >(i) and (i) + = 75 then credit mark] (iii) 25 each for mark 3 (b) stove because more of the energy heats up room / heats the room more or less energy escapes up chimney / less energy wasted [Do not allow less waste with the stove] or no un burnt fuel in smoke reason for mark [4] Page 30 of 3
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