"A 1000 W microwave" means that the microwave uses the power of 1000 Watts when it is on. Power is the rate of the consumption of energy:
`P = (Delta E)/(Delta t)` , assuming the energy is consumed at the constant rate. Here, `Delta E` is the energy consumed in the time interval `Delta t` .
So, if the microwave was on for 0.15 hour, it used the amount of energy
`Delta E = P*Delta t`
`Delta E = 1000 W * 0.15 h = 150 W*h = 0.15 kW*h` (kilowatt-hour, which is common unit of measuring the energy use in the household.)
In metric system, the energy is measured in Joules. Since `1 W = (1 J)/ (1 s)` , the time needs to be converted to seconds:
1 hour = 60 minutes = 60*60 seconds = 3600 seconds.
Then, the amount of energy used by the microwave would be
0.15 W*h = 0.15 W *3600 s = 540 Joules.
The amount of electric energy used is 0.15 kW*h, or 540 Joules.