Question

An electric heating element is connected to a 110 V circuit and a current of 3.2 A is flowing through the element. How much energy is used up during a period of 5 hours by the element

Answer 1

Power (rate of using energy) = (voltage) x (current)

Power of this heating element = (120 V) x (3.2 A) = 384 watts


The easy way:

     384 watts = 0.384 kilowatt

     (0.384 kilowatt) x (5 hours) = 1.92 kilowatt-hour


Another way:
     
                            384 watts = 384 joules per second .

        (384 joule/sec) x (3600 sec/hour) x (5 hours)  

=      (384 x 3600 x 5) (joules)  =  6,912,000 joules.

Answer 2

Wouldn't it be 110V * 3.2A * 5 hours? 

The problem shows 110V not 120V

So it would be 110V * 3.2A = 352

And 352 * 5 = 1760