Question

The national grid supplied a house with 18000000 J of energy in 1 hour. What was the average current supplied to the house in that hour? Write any equations that you use.

Answer 1

Electrical power  =  (voltage) x (current)

Electrical energy  =  (power) x (time)

Combine those definitions:

             Energy  =  (voltage) x (current) x (time)

Divide each side by (voltage x time), and we have

             Current  =  Energy / (voltage x time)

You told us that

             Energy = 1.8 x 10⁷ joules

             Time  =  1 hour  =  3,600 seconds

so we have 

             Current  =  (1.8 x 10⁷) / (voltage x 3,600).

If you live in the US, Canada, or Mexico, your voltage is 120 volts.

             Current = (1.8 x 10⁷) / (120 x 3,600)  =  41-2/3 Amperes

If you live practically anywhere else in the world, your voltage is 240 volts.

              Current = (1.8 x 10⁷) / (240 x 3,600)  =  20-5/6 Amperes.