Lesson: Chapter 10 — Power and energy in electrical appliances

10.2. Electrical energy used by appliances 2 of 2

Worked examples

Two examples from the textbook.

Example 1 — a car's 50 W headlamp is left on for 1½ hours. The energy used?

E = Pt

E = 50 × 1.5 × 60 × 60 J

E = 270 000 J

Example 2 — a 6 V bicycle bulb takes 0.6 A for 5 minutes. The energy used?

E = VIt

E = 6 × 0.6 × 5 × 60

E = 1080 J

Time in seconds

For an answer in joules, time must be in seconds: hours and minutes are converted first.