Student book answers Chapter 2

Transcription

1 P2 2.1 Food and fuels In-text A joules B Three from: wood, oil, coal, gas How far? 50 g of chocolate contains: = 750 kj You would need to run for: = 12.5 minutes This means you will need to run: = 1875 m 1 food, fuels, joules, breathing, bones, muscles, brains (6 marks) 2 20 minutes (2 marks) 3 Example answers (6 marks): Identifies a range of activities. Identifies the time that he/she spends doing each activity. Identifies the energy used per minute for the activities using the table. Calculates the energy for each activity by multiplying the time by the energy per minute. Identifies the energy stored in bananas, peas, chips, and chocolate from the table. Works out the mass of each that would be needed for the daily activities. Comments on the contrast in mass between fruit and chips/chocolate. P2 2.2 Energy adds up In-text A Energy cannot be created or destroyed. It can only be transferred. B light, sound, electricity Remember those stores! Credit suitable mnemonics using the letters C, T, K, G, and E. 1 created, destroyed, chemical, thermal, cannot (5 marks) 2a The battery has chemical energy. (2 marks) b Chemical energy transferred to thermal energy by electricity and light. (2 marks) 3 QWC question (6 marks). Example answers. There is a chemical store associated with the wood (and oxygen). The wood burns in the oxygen. Energy is transferred to the sausages. Because the fire heats the sausages. There is more energy in the thermal store associated with the sausages. There is more energy in the thermal store associated with the air. There is less energy in the chemical store associated with the wood. P2 2.3 Energy and temperature In-text A temperature: degrees Celsius ( C); energy: joules (J) B They move/vibrate faster. C When objects end up at the same temperature after energy transfer. Hot and cold Shut the door, you will let the warm air out. (Energy moves from hot places to cold places.)

2 1 temperature, thermometer, temperature, energy, solids, equilibrium (6 marks) 2 a cup of water at 30 C, a saucepan of water at 30 C, a saucepan of water at 50 C (1 mark) 3 QWC question (6 marks). Example answers: The particles in the metal tray vibrate. The hotter the tray the more they vibrate. When the tray goes into the oven the metal heats up. The particles on the outside of the tray vibrate more. They pass the vibrations on. The tray reaches the same temperature as the inside of the oven. The tray is in equilibrium. When you take the tray out of the oven it cools down. The energy moves from the thermal store of the tray to the thermal store of the air. The air heats up. The tray reaches the same temperature as the air. The particles in the tray vibrate less. P2 2.4 Energy transfer: particles In-text A A material that transfers energy quickly. B A material that does not transfer energy quickly. How fast? The plan should include timing how long it takes for water at a certain temperature to cool down, the need for repeat measurements, how variables are controlled, and a range of measurements of temperature. Risk assessment should include sensible suggestions to avoid damage/injury from hot water. 1 conduction, temperature difference, convection, move, slowly (6 marks) 2a The particles in a solid are close together, so can pass on the vibration; the particles in a gas or in a liquid are too far apart. (2 marks) b The particles in a gas or in a liquid can move; the particles in a solid cannot. Convection involves the movement of particles to transfer energy. (2 marks) 3 QWC question (6 marks). Example answers: The metal element gets hot. The particles in the metal vibrate more. Energy moves from the element to the water in contact with the element. The hot water molecules move faster. The hot water becomes less dense. Hot water floats up. Cooler (denser) water sinks to replace it. A convection current forms. The water circulates until all the water is hot. P2 2.5 Energy transfer: radiation In-text A two from: Sun, fire, light bulb B It is reflected. Cooling down a first measurement for shiny white; first measurement for shiny black b 14, 16, 13, 12.5 c The ranges overlap.

3 1 sources, radiation, temperature, reflected, absorb, medium, vacuum (7 marks) 2a White surfaces reflect infrared radiation so the houses will absorb less and stay cooler. (1 mark) b The fire emits infrared radiation so the camera cannot distinguish between the infrared radiation from the people and the infrared radiation from the fire. (2 marks) 3 Visual summary example answers (6 marks): All objects emit infrared radiation. This is commonly referred to as thermal radiation or heat. Infrared is a type of wave. Can travel through a vacuum. Can be reflected. Can be absorbed. Transfers energy. Cannot be seen by eye. P2 2.6 Energy resources In-text A coal, oil, and gas B carbon dioxide C Any three from: solar, wind, wave, geothermal, hydroelectricity, tidal, or biomass. Chris the carbon atom Story to include: tree dies, buried, over millions of years turns to coal, burnt, combines with oxygen to make carbon dioxide. 1 non-renewable, fossil fuel, renewable, power station (4 marks) 2 Burning coal produces steam. Steam drives a turbine. The turbine drives a generator. The generator generates electricity. (4 marks) 3 Credit any suitable board game, for example, snakes and ladders or collecting cards/tokens relating to different types. Points/board relates to ways fuels are formed or ways electricity is generated. Point system includes ideas about climate change/pollution. Board game must have a suitable scoring method relating to advantages and disadvantages of each method of electricity generation. P2 2.7 Energy and power In-text A watt (W) B kilowatt hour (kwh) What s the cost? a energy = 10 kw 1 h 7 days = 70 kwh b cost = 70 kwh 10 p 100 = 7 1 joules, watts, second, kwh, lower, less (6 marks) 2a power = potential difference current = 3 V 0.2 A = 0.6 W (2 marks) b energy = = 6 Ws (2 marks) 3 QWC question (6 marks). Example answers: The power rating tells you the energy that each kettle can transfer per second. The higher the power, the quicker the element will transfer energy to the water. The higher the power, the quicker the temperature of the water will rise. A power of 1200 W is the same as 1.2 kw (or 2 kw is the same as 2000 W). The 2 kw kettle will heat water faster than the 1.2 kw kettle. The energy that you pay for is measured in kilowatt hours (kwh). The energy that you pay for depends on the power and the time that you use it for.

4 P2 2.8 Work, energy, and machines In-text A work (J) = force (N) distance (m) B levers, gears 1 force, distance, machine, lever, force, gear, conservation, energy (8 marks) 2a lever (1 mark) b work done = force distance = 200 N 0.25 m = 50 J (2 marks) 3 Climbing Mount Everest: Work done = force distance = 600 N m = J Climbing upstairs to bed: Work done = force distance = 600 N 2.5 m = 1500 J Comparing the two: J 1500 J = 4000 so climbing Mount Everest requires 4000 times the work. (4 marks) 4 QWC question (6 marks). Example answers: A small force acting over a big distance produces a big force. The big force cannot move a large distance because this would mean a larger output of energy than input. Law of conservation of energy applies in gears as well. Gears work on rotational movement. work done = force distance You do work when you apply a force over a distance on the pedal. The law of conservation of energy says that energy cannot be created, so you cannot get more energy out than you put in.

5 P2 summary End-of-chapter 1 wind, solar, geothermal (1 mark) 2a C (1 mark) b kw, watts, kilowatts, W (1 mark) 3a Purple solid dissolves, the Bunsen burner heats the water around the solid, and the purple colour diffuses throughout the water in a convection current. (3 marks) b Any three from: Water is heated by the Bunsen burner. The water molecules move faster. The water expands/becomes less dense. Hot water floats. This is replaced by cold water, forming a convection current. 4a coal/oil/gas. (1 mark) b Fossil fuels are formed from the remains of plants and animals that died millions of years ago. (1 mark) c When all fossil fuels are burnt there will not be any more as they take millions of years to form. (2 marks) 5a gravitational potential (1 mark) b i Energy is conserved/cannot be lost. (1 mark) b ii Some energy is transferred/dissipated to the thermal store as the ball falls through the air. (1 mark) c There is a force (of gravity) acting on the ball. (2 marks) 6a work done = force distance = 500 N 200 m = J (2 marks) b work done = force distance = 50 N 1.5 m = 75 J (2 marks) 7a power = energy time = 6000 J 60 s = 100 W (2 marks) b power = current p.d. = 0.05 A 240 V = 12 W (2 marks) c 12 W bulb, since kwh is lower and therefore it is cheaper to use this lightbulb. (2 marks) 8a Energy is transferred by conduction through the inner pane of glass/passed on by vibrations from the hot room. Air inside the gap heats up/conduct occurs very slowly through the air. Energy is transferred by conduction through the outer pane of glass/passed on by vibration to the cold air outside. (3 marks) b The rate of transfer would decrease. There is no air to transfer the energy between the panes. Conduction will not occur/energy would be transferred very slowly by radiation. (3 marks) 9 This is a QWC question. Students should be marked on the use of good English, organisation of information, spelling and grammar, and correct use of specialist scientific terms. The best answers will explain in detail how insulation reduces energy bills (maximum of 6 marks). Examples of correct scientific points: Energy is transferred from a warm house to the cold air outside. Energy is transferred by conduction, convection, and radiation. To keep a house at the same temperature it needs to be heated. A lot of insulators trap air. Air is a poor conductor. Insulators reduce the rate of transfer of energy to the surroundings. The rate at which you need to heat the house to maintain the temperature decreases. A lower power heater is needed/heating is required for less time. This reduces the number of kwh of energy used. This will cost less money.

6 Answer guide for Big Write Developing Secure Extending 1 2 marks 3 4 marks 5 6 marks Design a simple diary that students could use to log what they eat/the activities that they do. Describe some foods and their energy content. Describe the energy used in some activities. Design a diary that students could use to log what they eat/the activities that they do. Describe in detail foods and their energy content. Describe the energy used in many activities. Design a detailed diary that students could use to log what they eat/the activities that they do.