The City School. THERMAL ENERGY - (Heat Energy)

Transcription

1 The City School What s the temperature? Southern Region THERMAL ENERGY - (Heat Energy) 1 In the middle of July, if the temperature outside were 20 C you might comment, It s quite cool today. However, in January if the temperature outside were 20 C you might say, It s unusually warm today. Explain why you would describe the same temperature so differently. 2 The diagram shows the mercury level in some thermometers. What temperature is each thermometer showing in degrees Celsius? a b c a Suggest three reasons why mercury is a good liquid to use in thermometers. b Suggest one disadvantage of using mercury in a thermometer. 4 Why would you use an alcohol thermometer rather than a mercury thermometer to measure the temperature in a freezer? 5 Here are some temperatures. 10 C 0 C 10 C 20 C 29 C 37 C 58 C 98 C 100 C 110 C Which of these temperatures is: a the temperature of melting ice? b normal body temperature? c the temperature of boiling water? d the temperature in a freezer? e air temperature on a hot summer day?

2 Warming up and cooling down 1 The table shows the results for a cooling experiment. The water in two beakers A and B was allowed to cool and the temperature was recorded every minute. Time (minutes) Temperature of water Temperature of water in beaker A ( C) in beaker B ( C) a Plot a graph of temperature (y-axis) against time (x-axis) for the water in beaker A. Draw the best-fit curve and label it A. b On the same axes plot the points for temperature against time for beaker B. Draw the best-fit curve and label it B. c In which beaker did the water cool more quickly? Explain how you can see this on the graph. d The two beakers were the same size and contained the same volume of water. Suggest why the water in one beaker cooled more quickly than the water in the other beaker.

3 Temperature and heat energy 1 The sparks from a sparkler at a Bonfire Night party are very hot. Each spark is a tiny piece of white-hot iron. If these white-hot sparks hit your clothes, they do not burn the clothing. Explain why something so hot does not burn your clothes. 2 List the following objects in order, in two different ways: a in temperature order - highest temperature first b in heat energy order - the one that you think contains most heat energy first. Objects a beaker containing 100cm 3 of water at 100 C a beaker containing 500cm 3 of water at 90 C an ocean with an average temperature of 5 C a 100cm 3 lump of copper at 95 C 3 If you placed a 1kg block of ice at 0 C into a bucket of water at room temperature (20 C), what might you expect the temperature of the water to be: a after 5 minutes? b the next day? Choose from these answers: 10 C 0 C 10 C 20 C 30 C 4 Two identical electric kettles are switched on at the same time. Kettle A contains 1 litre of water, and kettle B contains 0.5 litres of water. In both kettles the temperature of the water is 20 C. The water in kettle A takes longer to reach boiling point than the water in kettle B. Why is this?

4 What are conductors and insulators? 1 A metal rod is heated at one end. The heat travels along the rod by conduction. Explain, in terms of particles, how the process of conduction occurs. 2 A sauce pan is made mainly of steel, wood but it has a copper bottom and a steel handle made of wood. Explain the reasons for the use of each of these three materials. copper 3 On a cold day, the steel handlebars on a bicycle feel colder than the rubber handlebar grips. Explain why this is. 4 Diagram A shows two metal rods, X and Y, that are made of different metals. They are the same length and thickness. They are coated with wax and the ends are fixed through the walls of a can. Hot water is poured into the can and the wax begins to melt. After a few minutes the apparatus is as shown in diagram B. diagram A can diagram B rod X rod Y rod X rod Y can wax wax wax wax a Explain why the wax melts. b Explain why more wax melts on rod Y than on rod X. 5 Rewrite the following list of materials in order of thermal conductivity. Write the best conductor first and the poorest conductor last. aluminium copper ice polystyrene wood 6 In winter, birds fluff up their feathers to keep warm. Explain why fluffing up the feathers helps birds to keep warm. winter summer

5 Expanding and contracting 1 The diagram shows apparatus used for demonstrating that a metal rod expands when heated. bench clamp heater iron rod pointer pivot support a Explain why the pointer moves along the scale when the rod is heated. b Why is it necessary to have a long pointer? c Explain what happens to the pointer when the rod is allowed to cool. scale 2 The diagram shows some telephone wires that have been put up in warm weather. Why is it important that the wires have been left slack? 3 Explain why a metal screw cap on a glass jar can often be unscrewed more easily after being warmed in hot water. 4 Explain why a milk bottle would probably crack if boiling water were poured into it. 5 If you were heating some cold water in a beaker to a temperature of about 60 C, why would it not be sensible to fill the beaker to the top with cold water? thermometer beaker water heat 6 When a gas canister used for a camping stove has run out, it does, in fact, contain gas at atmospheric pressure. No more gas comes out because to do so its pressure has to be greater than atmospheric pressure. Explain why it would be extremely dangerous to throw the canister on to a fire.

6 onvection 1 The flickering effect on many electric fires is produced metal vanes by a set of vanes pivoted above a coloured lamp. Explain how this makes the flickering effect. coloured lamp 2 The freezer compartment inside a refrigerator is at the top of the cabinet. freezer compartment refrigerator salad Explain, in terms of convection: a why it is at the top b why the refrigerator would be ineffective if the freezing compartment were at the bottom. 3 The diagram shows a model mine. The smoke represents fresh air. The candle represents a fire. smoke straw glass tube glass tube Use your knowledge of convection to explain how the fire produced a flow of fresh air in the mine for the miners to breathe even though they were deep in the mine.

7 Radiation and energy escape 1 A vacuum flask is designed to reduce heat transfer by conduction, convection and infrared radiation. Which parts of the vacuum flask are designed to reduce heat transfer by: a conduction? b convection? c infrared radiation? Briefly explain your answer in each case. stopper vacuum glass hot liquid liquid y y silvered surfaces 2 A vacuum flask is usually used to keep liquids hot. However, it can also be used to keep a cold liquid cool. a Explain how it works in this case. b Why would it not be sensible to have ice cubes in the cold liquid in the flask? 3 A magnifying glass can be magnifying used to focus light from the glass Sun on to a piece of paper. At the point where the light is focused, the paper may char or burn. a Explain the similarity between light and infrared radiation that this shows. paper b State two other similarities between light and infrared radiation. 4 The diagrams show three ways that heat losses from homes can be reduced. a b c spot of light brick v a c u u m glass glass glass air double glazing roof insulation fibreglass insulation y y y y foam Explain how each of them helps to prevent heat losses. cavity wall insulation

8 Explaining changes of state 1 The diagram shows the A heating B cooling apparatus used in an experiment to record the thermometer temperature as a substance cools. The substance was heated until it was all molten, and then it was allowed to cool. The clamp temperature was taken as the substance cooled. The readings are shown in the table. boiling water Time (minutes) Temperature ( C) a Use the data in the table to plot a graph of temperature (y-axis) against time (x-axis). b Use your graph to answer these questions: i What is the melting point of the substance? Choose from: 110 C 90 C 70 C 50 C 20 C ii What was room temperature? iii What was the temperature at 3 minutes? c Describe the state of the substance in the tube at the following times. Choose from: solid liquid gas i after 2 minutes ii after 5 minutes iii after 10 minutes d Copy and complete the following passage by choosing the correct words from the list below. melting heat energy constant slowing closer temperature level boiling particles As the substance cools, it gives out energy and its drops. At the point the temperature stays The in the substance are down and moving together. While this is happening, is released which stops the substance from cooling down.

9 What can a magnet do? 1 Which of these metals are attracted to a magnet? copper zinc aluminium iron cobalt nickel steel gold 2 a Do these pairs of magnets attract or repel each other? b What happens if they are allowed to move? A B C 3 Describe a simple experiment that you could do at home to show that a baked bean tin is made out of iron. 4 Your fridge door is probably held shut by a strip of magnetic rubber. a What are the door and door frame made of? b Where is the magnetic rubber strip? c Explain why this arrangement holds the door shut. fridge fridge door handle plastic gasket attached to fridge door 5 Which of these stay together when they are picked up? Explain your answers carefully. A B C N N S S iron

10 Heating and cooling 1 Some students are doing a heating experiment. They are recording the temperature of water. thermometer water heat a What is the boiling point of water? b Copy and complete this sentence. Energy flows from the Bunsen burner flame to the water because there is a... 2 A steel sauce pan has a wooden handle. steel wood a Why would it not be sensible to use a metal handle? b What property of wood makes it a good choice for the handle? c Suggest another material that could be used to make the handle. 3 a Copy the diagram below and draw in two arrows to show the convection currents that are set up when the water is heated. water purple crystal heat

11 Heating and cooling continued b Explain why the hot water moves. c Sketch the diagram below. Add to it to show the convection currents in air that you would expect around a bonfire. (2 marks) d Air is a poor conductor of heat. Why does the air around your house not keep the house warm? 4 Study the diagram of an iron rod being heated. a What happens to the length of the rod when it is heated and then allowed to cool? b Explain what happens in terms of the particles of iron in the rod as the rod cools. (2 marks) clamp stand iron rod heat drinking straw pin wooden block 5 In an experiment, the apparatus was set up as shown in the diagram. a The flask was heated gently. What would you see in the water? b What would happen to the air in the flask as it was heated to cause this? c What would happen to the air in the flask as it cooled? d What would happen to the water in the beaker as the flask cooled? air flask water

12 Heating and cooling continued 6 a The diagram below shows cups of hot drinks at different temperatures. Which one will lose heat fastest? thermometer air temperature 20 C 40 C 56 C 34 C A B C b Which diagram below shows the best insulation to reduce the heat loss from a cup? thermometer water paper aluminium foil A B C c Most good insulators are made of materials that have lots of air spaces. Why does this make them good insulators? fibreglass

13 The City School Southern Region SOUND ENERGY

14 How are different sounds made? 1 Look at the picture of a handbell. When you shake it by the handle, the bell rings. a What happens to the clapper when you shake the bell? b What happens to the metal of the bell when it is struck? If the ringer puts a finger on the metal bell while shaking it, the bell makes a dull noise instead of a ring. c Why doesn t the bell ring? The bell is part of a set. Smaller bells have a higher pitch and larger bells have a lower pitch. d Why will the size of the bell affect its pitch? 2 A humming-bird flaps its wings very fast. This makes a humming sound, which is how the bird gets its name. What will happen to the pitch of the hum if the humming-bird: a flaps its wings more slowly? b flaps its wings more quickly? bell clapper handle 3 Here are some CRO traces (graphs) of different sounds, from tuning forks and from musical instruments. a Which of these sounds is the loudest? b Which is the quietest? c Which of these sounds is the highest pitched? d Which is the lowest pitched? e Which sounds were made by tuning forks? f Which sound has the largest amplitude? g Which sound has the lowest frequency? sound A sound C sound E Time Time Time sound B sound D sound F Time Time Time

15 How does sound travel through solids, liquids and gases? 1 Sometimes people put their ear to the door or wall to hear what is happening on the other side. American Indians put their ear to the ground to listen for horses. Explain how these actions help us to hear better. 2 There are lots of boats and ships with engines travelling across the oceans of the world. How might this affect communications between animals like dolphins and whales? 3 This table shows the speed of sound in different materials. Use it to answer the questions. a In which of the materials does sound travel fastest? b Does sound travel faster in air or in water? c In which material does sound travel twice as fast as in water? Material Speed of sound (m/s) air 330 water 1500 brick 3000 iron 5000 d Look at the picture. Order these statements, from the one who is first to hear or feel the sound vibrations to the one who is last. Write the letters in order. A The person on the path hears the sound. B The dog hears the sound through the brick wall. C The bird on the railing feels the vibration through its feet. D The fish feels and hears the sound through the water. 4 The Sun is a huge, hot, bright ball of gas. We can see it easily, but we can t hear it. A student says that is because it is a long way away, but we can still see it. a Why can t we hear the Sun burning? b Science fiction films are not always very good at showing how sound behaves. Give some examples of things that make a lot of noise on Earth but would happen silently in space.

16 How do we hear sounds? The ear semicircular canals object vibrates ear bones ear canal auditory nerve air vibrates eardrum cochlea hairs collects the sound vibrations pass down the ear flap 1 Copy the flow diagram at the side of the page. Use the diagram of the ear to help you fill in the gaps. 2 Read this description of animals using ultrasound, and answer the questions. Ultrasound Ultrasound is the name we give to sound that is too high pitched for humans to hear. The frequency or number of vibrations each second is so high that our ears will not detect the vibrations. The first instruments for detecting ultrasound were developed in about They could detect frequencies up to 75000Hz (vibrations per second). Most humans can only detect frequencies up to or 20000Hz. These instruments detected signals from bats and from insects, which no one knew existed before. There are many singing insects we never hear, and more are being discovered. To make a sound, an animal has to produce a vibration. Very small animals can only make high-pitched sounds because they are not big enough to produce low-frequency vibrations. Some people can hear the high-pitched squeak of a mouse, but rats, mice, voles and hamsters make lots of much higher-pitched sounds when they are communicating with each other. One advantage of this is that some of their predators cannot hear such high frequencies, although cats can hear to 90000Hz. vibrates vibrate vibrations are passed to the liquid in the semicircular canals and the in the vibrate messages are sent along the to the brain a What is the highest frequency humans can hear? b Can cats hear higher frequencies than humans? c What is ultrasound? d When was ultrasound first discovered? e A short string gives a higher note than along string.how does this help to explain why insects make high-pitched sounds?

17 Can sound be dangerous? Our ears can hear a very wide range of sounds, from very quiet to very loud. But above a certain level the ear is damaged by the sound. This table gives a guide to the loudness of different sounds measured in decibels. Typical sound level (decibels) Sound 0 silence 30 ticking watch 30 whisper 60 normal conversation 1m away 70 busy street 80 alarm clock 80 inside a small car 90 automatic lathe 90 heavy truck 100 food processor at 1m 110 car horn at 6m 110 power mower at 1.5m 110 pop group at 1.5m 120 jet engine at 150m 130 pneumatic riveter or hydraulic press 1 a What is the sound level given for a car horn at 6m? b Explain why some of the sounds have distances given, such as at 6m. c Why do you think the table says typical sound level rather than just sound level? 2 a Choose ten sounds from the table and plot them on a bar chart to show the different sound levels. Make sure the scale goes up to at least 120 decibels. b Sound levels above 80 decibels are dangerous. The more time you spend hearing sounds above this level, the more likely your ears are to be damaged in the long term. Draw a red line marking the 80-decibel line across your bar chart, and label it dangerous level. c Which sounds on your bar chart are above this dangerous level? d Sound levels above 120 decibels are painful to the ears. Draw a line at 120 decibels across your bar chart, and label it painful level.

18 Investigating sound Ear protection The first picture shows a very noisy working area. In the second picture, changes have been made to reduce the noise levels. Write down all the changes you can see and explain how each one has helped reduce danger to people s ears.

19 Sound and hearing 1 Megan has connected this microphone to a cathode ray CRO oscilloscope (CRO) so that she can see traces of the sounds on the screen. a Megan strikes a tuning fork and holds it close to the microphone. This is the trace she sees: amplifier microphone She chooses a tuning fork with a lower pitch and repeats the experiment. Which screen shows the trace now? A B C D b A whistle from the next lab is being picked up on the screen: If Megan shuts the door, the whistle is much fainter. Which screen shows the trace now? A B C D

20 Sound and hearing continued 2 This bar chart shows the highest pitch that these four animals can hear. child dog elderly person bat A B C D bat dog a Write the correct animal for label C and for label D. b What is the highest pitch that the dog can hear? c Sound travels through the air and down the ear canal. Explain what happens to the eardrum when the sound reaches it. 3 Peter has made a musical instrument out of some metal tubing. He has cut different lengths and hung them from string. He hits them with a stick to make a sound. a When a tube is struck, what vibrates so that you hear the note? b What is meant by the frequency of the note? Write the correct letter. A the number of times the tube is struck each second B the number of vibrations of the air each second C the number of swings the tube makes each second D the number of vibrations of the striker each second

21 Sound and hearing continued 4 In this experiment a small radio is playing inside a bell jar. The air is pumped out so that there is a vacuum inside the bell jar. to pump a What will happen to the sound from the radio as the air is pumped out? b Why does this happen? c These astronauts are on the Moon. Tom claps his hands. Why doesn t Louise hear him clap his hands? d Tom flashes his torch at Louise. Will Louise be able to see the light from the torch? e Explain your answer to d. f Their radios suddenly stop working. Louise holds a metal hammer she has been using between her helmet and Tom s, like this: How does this help them to communicate?

22 Sound and hearing continued 5 Look at the cartoon. Scott has been to a loud rock concert. Speak up, I can t hear. I feel as if my ears are full of water. Next day. Hi Scott I can hear properly again, great! a Explain why Scott couldn t hear properly. b What should Scott have done to protect his hearing at the concert? When there is a lot of rain, a pump is used to pump away the water. This pump is next to the brick wall by Jack s bedroom. Some of the sound reaches him through the brick and some travels through the air. c Will the sound travel faster through the brick or the air? d Will the vibrations sound louder through the brick or through the air? e Describe what could be done to reduce the amount of noise reaching Jack s ears. Remember to say what you would do, and how this would help. f Jack says that your solution has helped because: A he fell asleep in less time B one pillow over his head stopped the noise whereas before he needed three C he couldn t hear the pump when he listened to his personal stereo D his mum s voice sounded louder than usual when she shouted at him to put out the light. Which one reason above shows most scientifically that the solution worked? Write the correct letter. (2 marks)

23 Sound and hearingound and hearing continued 2 This bar chart shows the highest pitch that different animals can hear. Some of the bars have not been labelled A B C D E F G bat dog child a What is the highest pitch that the child can hear? b One of the unlabelled bars represents the highest pitch an elderly person can hear. Is it A, C, E or G? 3 Scott goes to a rock concert. As sound enters his ear, describe what happens to each of these parts: a the eardrum b small hairs inside the cochlea c the auditory nerve. d After the concert Scott s hearing is not good - it feels as though his ears are full of water. Next day his hearing has recovered. Describe what happened inside Scott s ears during the concert. e Jack is going to another concert, but outdoors this time. What could he do to make sure his hearing isn t damaged this time? When there is a lot of rain, a pump is used to pump away the water. This pump is next to the brick wall by Jack s bedroom. Some of the sound reaches him through the brick and some travels through the air. f Will the sound travel faster through the brick or the air? g Will the vibrations sound louder through the brick or through the air? h Describe what could be done to reduce the amount of noise reaching Jack s ears. Remember to say what you would do, and how this would help. (2 marks) (2 marks)