TC 9-62
6-10. In an AC circuit, true power is calculated using the resistance (R) of the circuit, not
the impedance (Z). If the circuit produces a maximum output voltage of 10 volts across a
50-ohm load, use the following formula:
2
E
=
True Power
R
2
(10 V )
=
True Power
50 Ω
100
=
True Power
watts
50
=
True Power
2 watts
NOTE: All calculations are rounded off to two decimal places.
When the output voltage drops to 70.7 percent of the maximum voltage of 10 volts, then
use the following formula:
2
E
=
True Power
R
2
(7.07 V)
=
True Power
50 Ω
50
=
True Power
watts
50
=
True Power
1 watt
6-11. As you can see, the true power is 50 percent (half) of the maximum true power
when the output voltage is 70.7 percent of the maximum output voltage. However, if you
are using the output current of the above circuit, the maximum current would be as follows:
10V
= .2 A)
.2 amp (
Ω
50
The calculations are as follows:
True Power = I2R
True Power = (.2 A)2 (50Ω)
True Power = (.04 x 50) watts
True Power = 2 watts
6-4
TC 9-62
23 June 2005
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