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Measuring Electrical Energy

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Measuring Electrical Energy

Ch. 11

Energy: the ability to do work

Electrical Energy: energy transferred to an electrical load by moving electric charges. (symbol is E)

Joule (J): unit for measuring energy.

Because a joule is so small, energy is also measured in much larger units such as the watt hour and the kilowatt hour.

Electrical Energy = Voltage x Electrical Current x Time Interval

E = V x I (amps) x t (sec)

E = V x I x t

E = V x I x t

Calculate the energy released from a battery in a flashlight bulb that was switched on for 4.5 hours, in which the voltage drop was 6V and the current flowing through the bulb was 0.35A.

Calculate the energy released from a battery in a flashlight bulb that was switched on for 4.5 hours, in which the voltage drop was 6V and the current flowing through the bulb was 0.35A.

1 hour has 60 minutes

1 minute has 60 seconds

60 x 60 = 3600

So 1 hour has 3600 seconds (1 x 3600).

2 hours would have 7200 sec (2 x 3600).

E = ?J

V = 6V

I = 0.35A

T = 4.5 hours

x 60

270

x 60

16200 sec

E = V x I x t

E = 6V x 0.35A x 16200sec

E = 34020 joules

- Electrical power is used by us every day – washer, mp3, toaster, discman, etc…
- When you think about power – it means, how rapidly an appliance is using up electrical energy.
Ex. A 300w bulb uses up 3 times as much electrical energy as a 100w bulb.

- The symbol for electrical power is P and the unit for power is the watt (W).
Power = Voltage Drop x Current

P = V x I

P = V x I

P = V x I

V = P

I

I = P

V

P

V

I

P = ?W

V = 120v

I = 7.9A

P = V x I

P = 120V x 7.9A

P = 948 W

P = 600W

V = ?

I = 1.9A

The voltage would be 316V.

V = P

I

V = 600W

1.9A

V = 316V

E = ?J

V = 6V

I = 0.35A

T = 16200 sec

*16200sec ÷ 3600 =

4.5 hours

E = V x I x t

E = 6V x 0.35A x 16200 sec

E = 34020 joules

The energy released would be 34020 joules.

or

E = V x I x t

E = 6V x 0.35A x 4.5 hours

E = 9.45 Whours

The energy released would be 9.45 watt hours.

- Electrical energy is the energy transferred to an electrical load by moving electrons.
SI Unit – Joule

symbol – J

- Voltage drop (potential difference), electric current, time interval

E = ?J

V = 6V

I = 0.30A

T = 45 sec

E = V x I x t

E = 6V x 0.30A x 45 sec

E = 81 joules

The energy released would be 81 joules.

E = ?J

V = 9V

I = 0.50A

T = 2.5 hours

E = V x I x t

E = 9V x 0.50A x 2.5 hours

E = 11.25 watt hours

The energy released would be 11.25 Whours.

or

E = V x I x t

E = 9V x 0.50A x 2.5 (3600)

E = 40500 joules

The energy released would be 40500 joules.