REC Electrical Module Practice Test

Lighting energy use is found by multiplying how much power the light draws by how long it runs. The lamp’s power is the rate at which it uses energy, so E = P × t. For example, a 60 W bulb running for 2 hours uses 60 × 2 = 120 Wh (0.12 kWh). Since power can also be written as voltage times current, energy can be expressed as V × I × t, which is the same idea as Power × Time. The other options don’t correctly account for how energy accumulates: voltage times time would give volt-hours, not energy; resistance times time doesn’t describe the energy used; and energy can’t be stated as independent of time.