2. P O W E R

3. Remember when…… Let’s take a brief step back…. Let’s take a brief step back…. Let’s take a brief step back…. Let’s take a brief step back….

4. But first… Resistance = charge / current Resistance = charge / current Resistance = volts / amps Resistance = volts / amps So … charge = resistance X current So … charge = resistance X current current = charge / resistance current = charge / resistance resistance = charge / current resistance = charge / current

5. What is POWER? Power is defined as Power is defined as Units of Energy / Time Units of Energy / Time Electrical Power - the amount of electrical power converted to heat, light, sound or motion every second. Electrical Power - the amount of electrical power converted to heat, light, sound or motion every second. Electrical Power - the amount of electrical energy transmitted in a given unit of time. Electrical Power - the amount of electrical energy transmitted in a given unit of time.

6. Symbols of Power The symbol for power is P The symbol for power is P P = energy / time P = energy / time P = E/T P = E/T Energy is measured in joules Energy is measured in joules P = joules/second P = joules/second P = watts P = watts

7. The Watt Named in honour of James Watt (1736-1819) Named in honour of James Watt (1736-1819) 1 joule of electrical energy is converted into light and heat by a light bulb every second the power of the bulb is 1 watt. 1 joule of electrical energy is converted into light and heat by a light bulb every second the power of the bulb is 1 watt. 60 joules per second is 60 watts 60 joules per second is 60 watts

8. Using the equation… P = E / t P = E / t V (potential difference)= E (energy) / Q (unit of charge) V (potential difference)= E (energy) / Q (unit of charge) V = E /Q V = E /Q E = QxV or just QV E = QxV or just QV P = E / t becomes P = P = E / t becomes P = We know that is current (or I) …so We know that is current (or I) …so P = IVPower = Current x Potential Difference P = IVPower = Current x Potential Difference Remember = power is measured in watts Remember = power is measured in watts QV t QtQt

9. What you really need to know… Power (watts) = Current (amps) x Potential (volts) Power (watts) = Current (amps) x Potential (volts) A current of 13.6 A passes thr ough an electric baseboard heater when it is connected to a 110 V wall outlet. What is the power of the heater? A current of 13.6 A passes thr ough an electric baseboard heater when it is connected to a 110 V wall outlet. What is the power of the heater? I = 13.6 I = 13.6 V = 110 V V = 110 V P = IV = 13.6 x 110 P = IV = 13.6 x 110 P = 1496 watts or P = 1496 watts or P = 1.5 x 10 3 watts P = 1.5 x 10 3 watts

10. Power Ratings Some common household examples in watts: Some common household examples in watts: Hair dryer....................................1600 Hair dryer....................................1600 Deep Fryer.................................1500 Deep Fryer.................................1500 Portable Heater..........................1500 Portable Heater..........................1500 Iron............................................. 1000 Iron............................................. 1000 Vacuum Cleaner.......................... 600 Vacuum Cleaner.......................... 600 Portable Fan.................................150 Portable Fan.................................150 Television....................................150 Television....................................150 Computer.....................................150 Computer.....................................150 VCR...............................................40 VCR...............................................40 Stereo...........................................30 Stereo...........................................30 Light bulbs.................. 40, 60, 75 or 100 Light bulbs.................. 40, 60, 75 or 100 P(w) = IV I(a) = P / V V(v) = P / I Calculate the current in amps for these appliances

11. Nobody’s Perfect No device is perfect No device is perfect Some energy is always converted to heat Some energy is always converted to heat Some energy always escapes to the outside Some energy always escapes to the outside We can calculate efficiency of an appliance We can calculate efficiency of an appliance Efficiency % = (energy out / energy in) x100 Efficiency % = (energy out / energy in) x100