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Section 3.3 Measuring Energy Input and Output 1

Section 3.3 Measuring Energy Input and Output 1. p. 332 - 338. We use energy in every aspect of our life. Driving, ipods , heating our homes, cooking food, watching tv . How can we choose which type of energy to use? (ex: we could use electricity, gasoline, propane, hydrogen)

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Section 3.3 Measuring Energy Input and Output 1

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  1. Section 3.3 Measuring Energy Input and Output1 p. 332 - 338

  2. We use energy in every aspect of our life. • Driving, ipods, heating our homes, cooking food, watching tv. • How can we choose which type of energy to use? (ex: we could use electricity, gasoline, propane, hydrogen) • We need to measure the types and amounts of energy going into and coming out of the devices.

  3. Power • Power is the rate at which a device converts energy. • Unit of power is the watt (W). • 1 watt is equal to 1 joule per second • 1W = 1J/s • Ex: 44 W = 44 J/s • The faster a device converts energy, the greater its power rating. • Is an appliance with high watts or low watts better? Why?

  4. Is an appliance with high watts or low watts better? Why?

  5. Power formula • For an electrical device, the power is the current multiplied by the voltage. • P = I x V (watts = amps x volts) P I V

  6. Power Calculation Example A hair dryer has a power rating of 1000 W. It is plugged into a 120-V outlet. What is the current flowing through the hair dryer? • Known: Power (P) = 1000 W, Voltage (V) = 120 V • Unknown: Current (I) = ? • Formula: I = P/V • Solve: I = 1000 W/ 120 V I = 8.33A

  7. Energy • You can use the power rating of a device to determine the amount of energy the device uses (power is the rate at which a device converts energy). Energy formula Energy consumption of an electrical device is its input power multiplied by the time the device is used. E = P x t (joules = watts x seconds) E P t

  8. Energy Calculation Example A microwave oven has a power rating of 800W. If you cook a roast in the oven for 30 min at high, how many joules of electrical energy are converted into heat by the microwave? *Remember that W = J/s • Known: P = 800 W (J/s), t = 30 min 30 min = ? s 30min x 60 s/min = 1800s • Unknown: E = ? • Formula: E = P x t • Solve: E = 800 W x 1800s E = 1 440 000 J = 1.4 MJ

  9. Kilowatt Hours • It doesn’t take common electrical devices long to consume a large number of joules. • Because of this, the kilowatt hour is often used. • Energy calculation is the same, except you use hours instead of seconds, and kilowatts instead of watts. • 1 kW = 1000 W

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