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8th Grade Thermal Energy Study Guide 20151009 www.njctl.org 2
Thermal Energy Study Guide www.njctl.org 3
Part 1 Define the following terms and/or concepts 4
Temperature 1 5
2 Kinetic Energy 6
3 Thermal expansion 7
4 Thermal contraction 8
Potential Energy (between molecules) 5 9
6 Thermal Energy 10
Heat 7 11
8 Thermal Equilibrium 12
Conduction 9 13
10 Radiation 14
11 Convection 15
12 Conductors 16
Insulators 13 17
14 Specific heat 18
15 Thermodynamics 19
Work 16 20
17 1st law of thermodynamics 21
18 2nd law of thermodynamics 22
19 entropy 23
heat engine 20 24
Part 2 Directions: Select the answer choice that best completes the statement or answers the question. 25
21 When a liquid is cooled, the liquid molecules A spread farther apart. B move slower than before. C experience thermal contraction. D increase their kinetic energy. 26
22 This type of heat transfer can occur in outer space. A Conduction B Convection C Radiation D Entropy 27
23 An insulator is a material that has molecules that A are closely packed together. B move easily past one another. C do not transfer heat easily. D will shrink when heated. 28
24 The following objects are all heated from 10°C to 30°C. Which object will transfer the most energy to your hand? A 5kg apples B 2kg apples C 5kg gold D 2kg gold 29
25 Two objects of the same material but different masses are subjected to the same thermal energy input. A The object with less mass will experience a greater change in temperature. B The object with more mass will experience a greater change in temperature. C They will both experience the same change in temperature. D It is impossible to compare their changes in temperature without knowing the specific heat of the objects. 30
26 All of the following are examples of conductors except A Silver B Water C Air D Aluminum 31
27 A 80°C object and a 60°C object sit (not touching) in a 21°C environment. Which best explains what will happen. A Both objects will get warmer. B The warmer object will exchange heat with the environment at a slower rate. C The environment will get warmer. D The warmer object will cool down while the cooler object will stay the same temperature. 32
28 An example of heat transfer by convection is A touching a hot pan and burning your finger B water boiling in a pot on the stove C feeling the warmth of a campfire on your face D the sun warming the roof of a house 33
29 Which of the following is an example of energy conservation? A An apple hangs suspended from a tree. B A person stands on tiptoes. C A car waits at a red light. D A hockey puck slides to a stop due to friction. 34
30 When energy is transferred as heat, the amount of useable energy A decreases. B remains the same. C increases. D is always zero. 35
Part 3 Directions: Answer the following thoroughly. A table of specific heats is attached. 36
Substance Specific Heat (J/kg °C) Aluminum 897 Apples 3,300 Bricks 800 Carbon 709 Copper 385 Gold 129 Iron 449 Mercury 140 Steam 1,870 Tin 230 Water 4,186 Wood 1,700 37
31 How are temperature and kinetic energy related? 38
32 Describe what happens to motion and spacing of molecules when heated or cooled for a: A liquid B solid C gas 39
33 What does a thermometer measure? 40
34 Describe characteristics of the three temperature scales including freezing and boiling point of water for each. 41
35 Complete the following conversions: A 37 ° C to Fahrenheit B 384 Kelvin to degrees Celsius C 45 ° C to Kelvin D 45 ° F to degrees Celsius 42
36 Using the ideas of thermal expansion and contraction, describe how a liquid thermometer works. 43
37 Recall the video shown in class of the bimetallic strip that was bent when it was heated. Explain why it bent. (HINT: remember that the strip was made of two different metals) 44
38 When does potential energy between molecules increase? Decrease? 45
39 What two types of energy do molecules possess? 46
40 Explain why thermal energy and temperature, though related, are different. 47
41 Provide an example of when two substances might have the same temperature but different thermal energy. 48
42 Which will cool fastest initially in a room temperature room? Boiling water or lukewarm water? 49
43 How are heat flow and temperature differences related? 50
44 Will heat flow between two objects touching that have the same temperature? Why or why not? 51
45 Which direction does heat flow? Give an example. 52
46 What are the three methods of thermal energy transfer? Give a couple of examples of each. 53
47 Do all objects emit the same amount of radiation? Why or why not? 54
48 Conduction occurs primarily in solids. Why? 55
49 What is the primary difference between conductors and insulators? 56
50 Give several examples of conductors and insulators. 57
51 If you wanted water to boil quickly in a tea kettle, what kind of material would you use for the tea kettle? 58
52 If you wanted to maximize heat transfer, what kind of material would you use? How about if you wanted to minimize heat transfer? 59
53 If you have several spoons made of conducting materials and insulating materials, which will feel cooler to the touch and why? 60
54 Suppose you took a bite of pie that was at a certain temperature. The crust doesn’t burn you but the filling does. Using the idea of specific heat, explain why the filling burned you but the crust didn’t even though they had the same temperature. 61
55 State whether the variable is “inversely” or “directly” proportional to the temperature change. Provide an illustrative example for each. A mass B specific heat C thermal energy transferred 62
56 Calculate the heat input (or output) required to change the temperature of 3kg of iron by 3 degrees Celsius. 63
57 Calculate the final temperature of 0.020 kg of mercury that loses 500J of thermal energy and started with a temperature of 400Kelvin. 64
58 Calculate the change in temperature of 10kg of wood that gains 3,000J of thermal energy. 65
59 Give an example of the 1st law of thermodynamics in action. 66
60 What energy conversions are involved in a heat engine? 67
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