P O W E RP O W E R

Remember when……Remember when……

Let’s take a brief step back….Let’s take a brief step back….

But first…But first…

Resistance Resistance = charge / current= charge / current Resistance Resistance = volts / amps= volts / amps

So … So … charge = resistance X currentcharge = resistance X current current = charge / resistancecurrent = charge / resistance resistance = charge / current resistance = charge / current

What is POWER?What is POWER?

Power is defined as Power is defined as Units of Energy / TimeUnits of Energy / Time Electrical Power - the amount of electrical power Electrical Power - the amount of electrical power

converted to heat, light, sound or motion every converted to heat, light, sound or motion every second.second.

Electrical Power - the amount of electrical energy Electrical Power - the amount of electrical energy transmitted in a given unit of time.transmitted in a given unit of time.

Symbols of PowerSymbols of Power

The symbol for power is PThe symbol for power is P P = energy / timeP = energy / time P = E/TP = E/T

Energy is measured in joulesEnergy is measured in joules P = joules/secondP = joules/second P = wattsP = watts

The WattThe Watt

Named in honour of James Named in honour of James Watt (1736-1819)Watt (1736-1819)

1 joule of electrical energy is 1 joule of electrical energy is converted into light and heat converted into light and heat by a light bulb every second by a light bulb every second the power of the bulb is 1 the power of the bulb is 1 watt.watt.

60 joules per second is 60 60 joules per second is 60 wattswatts

Using the equation…Using the equation… P = E / tP = E / t V (potential difference)= E (energy) / Q (unit of charge)V (potential difference)= E (energy) / Q (unit of charge) V = E /QV = E /Q E = QxV or just QVE = QxV or just QV

P = E / t becomes P =P = E / t becomes P = We know thatWe know that is current (or I) …so is current (or I) …so P = IVP = IV Power = Current x Potential DifferencePower = Current x Potential Difference Remember = power is measured in wattsRemember = power is measured in watts

QVtQ

t

What you really need to What you really need to know…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 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 heater when it is connected to a 110 V wall outlet. What is the power of the heater?the power of the heater?

I = 13.6I = 13.6 V = 110 VV = 110 V

P = IV = 13.6 x 110P = IV = 13.6 x 110 P = 1496 watts or P = 1496 watts or P = 1.5 x 10P = 1.5 x 1033 watts watts

Power RatingsPower Ratings Some common household examples in watts: Some common household examples in watts: Hair dryer ....................................Hair dryer .................................... 1600 1600 Deep Fryer .................................Deep Fryer ................................. 1500 1500 Portable Heater ..........................Portable Heater .......................... 1500 1500 Iron ............................................. Iron ............................................. 1000 1000 Vacuum Cleaner.......................... Vacuum Cleaner.......................... 600 600 Portable Fan.................................Portable Fan................................. 150 150 Television ....................................Television .................................... 150 150 Computer .....................................Computer ..................................... 150150 VCR...............................................VCR............................................... 40 40 Stereo ...........................................Stereo ........................................... 30 30 Light bulbs.................. 40, 60, 75 or 100Light bulbs.................. 40, 60, 75 or 100

P(w) = IV I(a) = P / V V(v) = P / I

Calculatethe current in amps for

these appliances

Nobody’s PerfectNobody’s Perfect

No device is perfectNo device is perfect Some energy is always converted to heatSome energy is always converted to heat Some energy always escapes to the outsideSome energy always escapes to the outside We can calculate efficiency of an applianceWe can calculate efficiency of an appliance Efficiency % = (energy out / energy in) x100Efficiency % = (energy out / energy in) x100