Section 2 review
The process of making everyday items often requires the transformation of energy through many different forms, which can be followed as a flow of energy. Power is a basic quantity that measures the change in energy per unit time and has units of watts (W). Power is measured for many technologies all around us, such as light bulbs, batteries, automobile engines, washing machines, or stereo speakers. Voltage (measured in volts), electric current (measured in amperes), and power (measured in watts) are the most useful quantities for understanding the energy consumption of electric devices. Radiant energy spans the full electromagnetic spectrum, but our eyes can only see one small part of it called visible light. Read the text aloud
power, watt (W), ampere (A), volt (V), electric current, radiant energy, intensity, light, horsepower (hp), renewable energy

P= ΔE Δt = W Δt
P=IV

Review problems and questions

  1. Describe the energy flow that goes into producing a gold ring. Which step in the process do you think requires the most energy? Read the text aloud Show
  1. A 40 kg wheeled cart needs to be moved to the top of a platform that is 1.0 m high.
    1. How much power is required to pick up the cart and place it on the platform in 3.0 s?
    2. How much power is required to roll it 20 ft up a ramp, a process taking 20 s?
    3. How much power is required to roll it 40 ft up a shallower ramp, a process that also takes 20 s?
    4. Read the text aloud Show
  1. An immersion water heater is rated at 1,000 W. If it is plugged into a 120 volt outlet, how much current does it draw? Read the text aloud Show
  1. The cost of electricity in Mount Pleasant is 5 cents per kilowatt-hour.
    1. How much does it cost to operate a 100-W-rated incandescent light bulb for 24 hours?
    2. How much does it cost to operate a 100-W-rated fluorescent light bulb for 24 hours?
    3. How much does it cost to operate each for an entire year?
    4. Which one generates more light? Read the text aloud Show
  1. From the standpoint of energy and power, what are the advantages for a car with high horsepower? What are the disadvantages? Read the text aloud Show
  1. Why does ultraviolet light cause sunburn but infrared light does not? Read the text aloud Show

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