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1 | |
What units are used to express efficiency? |
| | A) | joules, because efficiency compares input and output energies, which are measured in joules |
| | B) | joules, because efficiency compares input energy and output work, which are both measured in joules |
| | C) | no units, because efficiency is a ratio of two measurements, so the units cancel |
| | D) | many different units, depending on the machine or process you are investigating |
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2 | |
A television set uses electrical energy and produces heat, light, and sound. What are the input and waste energies of a TV? |
| | A) | input: electrical
waste: heat |
| | B) | input: heat
waste: electrical |
| | C) | input: electrical
waste: light and sound |
| | D) | input: light and sound
waste: heat |
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3 | |
John claims that the useful output of some processes can be work or heat, instead of other forms of energy. According to the theory you have studied, is John correct? |
| | A) | Yes: work and heat can be useful output of an energy transformation. |
| | B) | No: work can be a useful output, but heat is always waste energy. |
| | C) | No: useful outputs are always forms of energy, and work is not energy. |
| | D) | No: neither work nor heat can be useful forms of output energy transformations. |
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4 | |
Which statement below is a correct statement of the second law of thermodynamics? |
| | A) | Energy transformations can be more than 100% efficient. |
| | B) | Energy transformations can be 100% efficient. |
| | C) | Energy transformations are always less than 100% efficient. |
| | D) | Energy transformations are 0% efficient. |
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5 | |
A simple pendulum is pictured below. What is the best description of the pendulum as it swings through the point marked B?
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| | A) | minimum kinetic energy; maximum gravitational potential energy |
| | B) | minimum kinetic energy; minimum gravitational potential energy |
| | C) | maximum kinetic energy; maximum gravitational potential energy |
| | D) | maximum kinetic energy; minimum gravitational potential energy |
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6 | |
A perfect pendulum would reach the same height at both ends of its motion. Suppose the ending height (h2) is much less than the starting height (h1). What is the best description of such a pendulum, if you think of it as an energy conversion device?
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| | A) | high efficiency, very little waste energy |
| | B) | high efficiency; lots of waste energy |
| | C) | low efficiency; lots of waste energy |
| | D) | low efficiency; very little waste energy |
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7 | |
A mid-efficiency natural gas furnace is 81% efficient. Suppose 500 J of chemical energy is released by burning gas in the furnace. What happens to the energy? |
| | A) | 95 J warm the house; 405 J escape through the chimney |
| | B) | 405 J warm the house; 95 J escape through the chimney |
| | C) | 81 J warm the house; 19 J escape through the chimney |
| | D) | 19 J warm the house; 81 J escape through the chimney |
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8 | |
An electric kettle uses 1.5 kJ of electrical energy per second. The kettle warms a litre of water to its boiling point in 4.5 minutes. To heat this amount of water, 335 kJ of thermal energy had to be added to the water. What is the efficiency of the kettle? |
| | A) | 0.83% |
| | B) | 2.0 % |
| | C) | 50% |
| | D) | 83% |
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9 | |
A microwave oven has efficiency of 47%. In one minute, the oven can add 42.4 kJ of thermal energy to a mug of hot chocolate. What is the total input energy to the oven during this time? |
| | A) | 90.9 kJ |
| | B) | 19.9 kJ |
| | C) | 1.11 kJ |
| | D) | 0.90 kJ |
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10 | |
Which energy transfer or energy conversion in the list below is most likely to have low efficiency? |
| | A) | kinetic energy of a tennis racquet to kinetic energy of a tennis ball |
| | B) | chemical energy of ATP to kinetic energy of the legs of a marathon runner |
| | C) | kinetic energy of a wrestler to elastic potential energy of the wrestling mat |
| | D) | kinetic energy of a fast-moving high-jumper to gravitational potential energy |
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11 | |
Inventors occasionally claim to have built devices that are more than 100% efficient. Jason argues that these claims are always mistaken, because 100% efficiency is impossible. Which statement of a scientific law best supports Jason's point of view? |
| | A) | The second law of thermodynamics says that thermal energy flows naturally from high temperature to low temperature objects. |
| | B) | The second law of thermodynamics says that no process can convert all thermal energy into useful work. |
| | C) | The first law of thermodynamics says that energy can be changed in form. |
| | D) | The first law of thermodynamics says that energy cannot be created or destroyed. |
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12 | |
More efficient energy technology has many advantages. Which of the following goals is much more important today than it was to early inventors like James Watt, who worked to improve the steam engine? |
| | A) | reduced operating costs |
| | B) | greater output of useful energy |
| | C) | increased reliability |
| | D) | reduced pollution and environmental damage |
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13 | |
Examine the chart below, which compares some characteristics of different technologies for producing light. What is a correct conclusion about the energy output of the light sources listed?
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| | A) | Standard light bulbs are more efficient than compact fluorescent bulbs. |
| | B) | Both compact fluorescent and standard bulbs produce more light than heat for a given energy input. |
| | C) | A great deal of electrical energy could be saved if more efficient light sources were developed. |
| | D) | Compact fluorescent bulbs are so efficient that there is no point trying to develop even more efficient light sources. |
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