Download Unit 7 Study Guide Answer Key

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Unit 7 Study Guide
7.1 – Temperature, Thermal Energy, and Heat
1. What is temperature?
The measure of the average kinetic energy of the particles that make up an object.
2. How are thermal energy and temperature related?
Thermal energy is the sum of the kinetic energy (temperature) and potential energy of particles.
Increased temperature = increased thermal energy
3. What is the difference between thermal energy and heat?
Heat is the energy that is transferred due to temperature differences.
Thermal energy is one type of energy that objects have.
4. How can you calculate changes in thermal energy?
𝑄 = 𝑚(𝑇𝑓 − 𝑇𝑖 )𝐶
5. Describe how the motions of particles that make up an object change when the object’s temperature increases.
Increasing the temperature means increasing the motion of particles.
6. Describe the energy transfer when you touch a block of ice with your hand.
Energy from your hand transfers to the ice, increasing the energy of the ice.
7. When one object heats another, does the temperature increase of one object always equal the temperature
decrease of the other object? Explain.
Only if the 2 objects have the same mass and same specific heat (meaning they are the same material).
Otherwise, no.
8. Explain why water is often used as a coolant.
Because it has a relatively high specific heat (it takes a lot of energy to heat it up so it will absorb a lot
of energy before heating up).
9. Estimate the change in thermal energy of water in a pond with a mass of 1000 kg and a specific heat of 4200 J/kgoC if
the water cools by 1oC.
Q = 1000(1)(4200) = 4,200,000 J
Q = m ∆T
C
10. Calculate the specific heat of a metal if 0.3 kg of the metal absorb 9000 J of heat as the metal warms by 10 oC.
𝐶=
𝑄
9000
=
= 3000 𝐽/𝑘𝑔℃
𝑚∆𝑇 0.3 × 10
7.2 – Conduction, Convection, and Radiation
11. What are conduction, convection, and radiation?
Conduction – thermal energy transfer by collisions between particles
Convection – thermal energy transfer by movement of fluids
Radiation – energy transfer by electromagnetic waves
12. How do thermal conductors differ from thermal insulators?
Conductors – allow energy to transfer more easily and quickly
Insulators – slows energy transfer
13. How are thermal insulators used to control the transfer of thermal energy?
They keep the thermal energy in by limiting conduction and convection.
14. Identify which method of energy transfer would be fastest through a vacuum, which would be fastest through a gas,
and which would be fastest through a solid.
1. Radiation; 2. Convection; 3. Conduction
15. Explain why the air temperature near the ceiling of a room tends to be warmer than the air temperature near the
floor.
Because hot air rises due to more energetic particles which decreases the density of the air.
16. Predict whether plastic foam, which contains pockets of air, would be a good thermal conductor or a good thermal
insulator.
Insulator because it would limit conduction because of the air pockets (imagine a Styrofoam cup filled
with hot coffee).
17. Several days after a snowfall, the roofs of some home on a street have almost no snow on them, while the roofs of
other homes are still snow-covered. Give one reason, related to home insulation, that might cause this difference.
The homes with snow have insulation in their roof while those without snow do not.
7.3 – Using Thermal Energy
18. What are some common types of heating systems?
Forced-air systems, radiator systems, solar heating systems
19. What are the first and second laws of thermodynamics?
1st Law – to increase temperature of a system, heat must be added or work must be done
2nd Law – energy spreads from high concentration to low concentration areas
20. How does an internal combustion engine work?
It uses thermal energy from the burning of gasoline to move a piston up and down which causes
the car to move.
21. How does a refrigerator work?
A coolant vapor surrounds the main body of the refrigerator, allowing thermal energy to leave the
interior, cooling it off.
22. Describe a device that transforms thermal energy into another useful form.
A heat engine; a solar collector
23. Explain how the thermal energy of an isolated system changes with time if the mechanical energy of that system is
constant.
The thermal energy is equal to the sum of the thermal energy transferred in and the work the system
does (aka 1st Law of Thermodynamics).
24. Compare and contrast an active solar heating system with a radiator system.
Active solar - radiation heat water  water sent by pipes to heat rooms
Radiator – furnace heats water  water sent by pipes to heat rooms
25. Predict whether energy will ever spontaneously transfer from a cold pot of water to a hot stove.
No, it goes against the 2nd Law of Thermodynamics.
26. Suppose you vigorously shake a bottle of fruit juice. Predict how the temperature of the juice will change. Explain
your reasoning.
It will increase because you have increased the motion of the particles which increases the
kinetic energy and the temperature.