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Energy & Transformations. Power & Efficiency. Power. Power: The rate of doing work or transferring energy. Measured in Watts (W) 1 W = 1 J / s (joule per second) It is given by: Watts are commonly used to measure the power used by electrical appliances. Where: P=power (W)
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Energy & Transformations Power & Efficiency
Power • Power:The rate of doing work or transferring energy. • Measured in Watts (W) • 1 W = 1 J / s (joule per second) • It is given by: • Watts are commonly used to measure the power used by electrical appliances. • Where: • P=power (W) • W = work (J) • ∆E = Energy transferred (J) • ∆t= time interval (s)
Example 1 • A runner transforms 3.5 x 105 J of energy running in the New York City Marathon. If it takes 3.25h to run, what is the runner’s power? Express in Watts & Kilowatts
Example #2 • A 45kg student climbs a flight of stairs 4m high in 25 seconds. Determine • The potential energy of the student at the top of the stairs. • The student’s power.
Efficiency • Efficiency: The ratio of the useful energy output of a device to the required input energy. • Typically expressed as a percentage (%). • It is given by:
Example #3 • An incandescent light bulb requires 1500 J of electrical energy to produce 150 J of light energy. • Write the energy transformation equation. • Calculate the efficiency of the light bulb. • Draw the energy flow diagram.
Example #4 • A 125 W ceiling fan produces 4500 J of wind energy in 48 seconds. Determine: • The power output of the ceiling fan • The efficiency of the ceiling fan • The energy flow diagram