Power is not the same as energy
The mistake
Using watts and joules interchangeably.
Why it feels right
Both describe 'how much work', so they blur together.
How to catch it
A term mixes W and J, or you forgot to multiply power by time.
The first principle
Power is the rate of energy transfer, P = E/t (watts = joules per second). Energy = power × time.
worked mini-example
A 60 W bulb runs for 2 hours. Energy used?
Common wrong move
60 J.
Correct
E = P·t = 60 · 7200 s = 4.32 × 10⁵ J.
Test the repair EN-05 · transfer
include J
Make a fresh prediction before referring to the worked example.