# Energy Ch 11 Presentation

Topics: Energy, Temperature, Heat Pages: 9 (1353 words) Published: October 22, 2012
11 Using Energy

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1. A machine uses 1000 J of electric energy to raise a heavy mass, increasing its potential energy by 300 J. What is the efficiency of this process? A. B. C. D. E. 100% 85% 70% 35% 30%

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2. When the temperature of an ideal gas is increased, which of the following also increases? (1) The thermal energy of the gas; (2) the average kinetic energy of the gas; (3) the average potential energy of the gas; (4) the mass of the gas atoms; (5) the number of gas atoms.

A. B. C. D. E.

1, 2, and 3 1 and 2 4 and 5 2 and 3 All of 1–5

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3. A refrigerator is an example of a A. B. C. D. E. reversible process. heat pump. cold reservoir. heat engine. hot reservoir.

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Example Problem
Light bulbs are rated by the power that they consume, not the light that they emit. A 100 W incandescent bulb emits approximately 4 W of visible light. What is the efficiency of the bulb?

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Efficiency

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Example Problems
A person lifts a 20 kg box from the ground to a height of 1.0 m. A metabolic measurement shows that in doing this work her body uses 780 J of energy. What is her efficiency?

A 75 kg person climbs the 248 steps to the top of the Cape Hatteras lighthouse, a total climb of 59 m. How many Calories does he burn?

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Checking Understanding
When you walk at a constant speed on level ground, what energy transformation is taking place? A. B. C. D. E. Echem  Ug Ug  Eth Echem  K Echem  Eth K  Eth

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Example Problem
How far could a 68 kg person cycle at 15 km/hr on the energy in one slice of pizza? How far could she walk, at 5 km/hr? How far could she run, at 15 km/hr? Do you notice any trends in the distance values that you’ve calculated? Chemical energy from food is used for each of these activities. What happens to this energy—that is, in what form does it end up?

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The Ideal Gas Model
2 Kavg T 3 kB

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Checking Understanding:Temperature Scales
Rank the following temperatures, from highest to lowest. A. 300 °C > 300 K > 300 °F

B.

300 K > 300 °C > 300 °F

C. 300 °F > 300 °C > 300 K

D. 300 °C > 300 °F > 300 K

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Checking Understanding
Two containers of the same gas (ideal) have these masses and temperatures: • Which gas has atoms with the largest average thermal energy? • Which container of gas has the largest thermal energy? A. P, Q B. P, P C. Q, P D. Q, Q

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Example Problem
Using a fan to move air in a room will make you feel cooler, but it will actually warm up the room air. A small desk fan uses 50 W of electricity; all of this energy ends up as thermal energy in the air of the room in which it operates. The air in a typical bedroom consists of about 8.0 x 1026 atoms. Suppose a small fan is running, using 50 W. And suppose that there is no other transfer of energy, as work or heat, into or out of, the air in the room. By how much does the temperature of the room increase during 10 minutes of running the fan?

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Example Problem: Work and Heat in an Ideal Gas
A container holds 4.0 x 1022 molecules of an ideal gas at 0 °C. A piston compresses the gas, doing 30 J of work. At the end of the compression, the gas temperature has increased to 10 °C.

During this process, how much heat is...