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Examples

Example 1

A circuit with an unknown load has an applied voltage of 100 volts. The measured current is 2 amperes. How much power is consumed?

 

P = IxE

P = 2A x 100 V = 200 W

 

Example 2

 

An electric toaster, rated at 550 watts, is connected to a 117 volt source.  How much current will this appliance use?

 

I = P/E

I = 550 W/117 V  =  4.7 A

 

 

Example 3

 

If a current of 0.05 ampere flows through a 22 ohm resistor, how much power is dissipated by the resistor?

 

First, find the voltage drop across the resistor using Ohm's law: IR = ER/R

ER = .05x22  ð ER = 1.1 volts

PR = IRER = (0.05)x(1.1) = 0.055 W

Example 4

Given a circuit with a voltage and resistor whose ratings ar given. What is the power consumed?

Find the total resistance for the circuit using the rules studied earlier.

Determine the total current flowing in the circuit using Ohm's law.

Find the power using the power formula