measuring electrical energy ch. 11. energy: the ability to do work electrical energy: energy...
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Measuring Electrical Energy
Ch. 11
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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.
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Calculation
Electrical Energy = Voltage x Electrical Current x Time Interval
E = V x I (amps) x t (sec)
E = V x I x tE = V x I x t
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Question to try
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.
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Question to try
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.
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Convert hours to seconds
1 hour has 60 minutes1 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).
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E = ?JV = 6VI = 0.35AT = 4.5
hoursx 60 270
x 6016200 sec
E = V x I x tE = 6V x 0.35A x 16200secE = 34020 joules
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Rate at which Energy is Used!
• 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.
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• The symbol for electrical power is P and the unit for power is the watt (W).
Power = Voltage Drop x Current
P = V x IP = V x I
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P = V x I
V = P I
I = P V
P
V I
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Calculate the power of a vacuum cleaner if the operating voltage is
120v, and the current flowing through it when it is used is 7.90A.
P = ?WV = 120vI = 7.9A
P = V x IP = 120V x 7.9AP = 948 W
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Calculate the voltage of a computer that has 600W of power and 1.9A
flowing into the monitor?
P = 600WV = ?I = 1.9A
The voltage would be 316V.
V = P I
V = 600W
1.9A
V = 316V
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Joules to Watt hours
E = ?JV = 6VI = 0.35AT = 16200
sec
*16200sec ÷ 3600 =
4.5 hours
E = V x I x tE = 6V x 0.35A x 16200
secE = 34020 joules
The energy released would be 34020 joules.
or
E = V x I x tE = 6V x 0.35A x 4.5 hours E = 9.45 Whours
The energy released would be 9.45 watt hours.
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P. 336 – 1, 2, 3a, 3b
1. Electrical energy is the energy transferred to an electrical load by moving electrons.
SI Unit – Joulesymbol – J
2. Voltage drop (potential difference), electric current, time interval
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3a
E = ?JV = 6VI = 0.30AT = 45 sec
E = V x I x tE = 6V x 0.30A x 45 secE = 81 joules
The energy released would be 81 joules.
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3b
E = ?JV = 9VI = 0.50AT = 2.5
hours
E = V x I x tE = 9V x 0.50A x 2.5 hoursE = 11.25 watt hoursThe energy released would be
11.25 Whours.or
E = V x I x tE = 9V x 0.50A x 2.5 (3600) E = 40500 joules
The energy released would be 40500 joules.