How much power is produced if a voltage of #3 V# is applied to a circuit with a resistance of #21 Omega#?

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Answer 1 · 2016-02-29T05:40:56

#3/7 W# or #428.571 mW#

Let P be power dissipated from 21 ohm resistor to ambient.

Let V be the voltage applied across 21 ohm resistor.

Let I be the current passing through 21 ohm resistor.

We know that power defined as the product of voltage across resistor and current through resistor

Therefore, #P=VI##------(1)#

By ohm's law, #V=IR#

#=>I=V/R##------(2)#

from (1) and (2)

#P=V xx V/R#

#P=V^2/R#

substitute V=3 volts and R=21 ohms

#=> P=3^2/21#

#=>P=9/21#

#=>P=3/7 #watts

#=>P=0.428571#watts

#=>P=428.571 mW#