HW 4.3: Efficiency

What is efficiency in terms of energy transfer?

• The amount of energy lost during transfer.

• The proportion of input energy converted into useful output energy.

• The rate at which energy is used.

• The total energy input.

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In a lamp, the light energy is considered the:

• Input energy.

• Waste energy.

• Useful energy output.

• Non-useful energy output.

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What type of energy is considered waste energy in a lamp?

• Electrical energy.

• Light energy.

• Thermal (heat) energy.

• Chemical energy.

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NGSS.HS-PS3-4

The formula for calculating efficiency in terms of energy is:

• Efficiency = total energy input + useful energy output.

• Efficiency = useful energy output ÷ total energy input.

• Efficiency = total energy input × useful energy output.

• Efficiency = useful energy output + total energy input.

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NGSS.HS-PS3-3

What efficiency value represents a device that is completely efficient?

• 1 or 100%.

• 0.5 or 50%.

• 1.5 or 150%.

• 2 or 200%.

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If a device has an efficiency of 0.75, what is this as a percentage?

• 50%

• 75%

• 100%

• 150%

If an incandescent bulb converts 45 joules of a 300-joule input to light energy, what is its efficiency as a decimal?

• 0.05

• 0.15

• 0.25

• 0.45

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An incandescent light bulb converts 300 J of electrical energy into 45 J of light energy. Meanwhile, a LED light bulb converts 300 J of electrical energy into 225 J of light energy. Which one is more efficient?

• The incandescent light bulb, because it produced less light energy so it saved more energy

• The LED light bulb, because it produced more light energy than the incandescent light with the same input energy

• They both have the same efficiency since they both used up 300 J of input energy

• This can’t be determined without knowing their power rating

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NGSS.HS-PS3-3

Can the efficiency of a device be more than 100%?

• No, because we haven’t achieved the technology capable of doing so

• No, because that would violate the law of conservation of energy

• Yes, most devices/machines are able to do this

• Yes, but it is only true for certain electronic devices

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NGSS.HS-PS3-4

For which device type might "waste" energy be considered useful?

• Lamp

• Electric heater

• Refrigerator

• Microwave

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