Measuring Electrical Energy

1. Measuring Electrical Energy Volts, Amperes, Ohms

2. conserving energy makes cents Toronto Hydro’s “Time of Use” billing for energy use On Peak 12.9¢/KWh Mid-Peak 10.9¢/KWh Off-Peak 7.2¢/KWh

3. Measuring Electric Energy • Three units measure different aspects of electric energy • Volts • Amperes • Ohms • A “plumbing” analogy helps us make sense of the meaning of these units

4. Voltage (V) • Voltage is a measure of the pressure forcing electrons through a circuit • Measured in Volts (V) • Voltage is like the water pressure in a pipe • Higher voltage = higher pressure

5. Voltage (V)

6. Current (I) • Current is the measure of the amount of electrons passing a point in a given amount of time • Measured in Amperes or Amps (A) • Current is like the flow rate of the water in the pipe, amount of water moving through the pipe

7. Current (I)

8. Resistance (R) • Resistance is a measure of how resistant an object is to the flow of electricity • Resistance is measured in ohms (Ω) • Resistance is like the size of the pipe carrying the water. A large pipe offers less resistance to the water flowing through

9. Resistance (R)

10. Energy = Voltage x Current X Time • To measure how much electrical energy an appliance is using we use the formula E = V × I × Δt or E = VIΔt E = energy in watts (W) V = voltage in volts I = current in amperes Δt = time in hours

11. Example 1 How much energy is used to completely recharge an iPhone if it uses 1.2 amperes of current at 4.5 volts for 2 hours? E = VI∆t Knowns: E = VI∆t V = 4.5 E = 4.5(1.2)2 I = 1.2 E = 5.4 (2) ∆t= 2 E = 10.8 W Therefore the iPhone uses 10.8 watts of energy