A light bulb is only 2% efficient, the wasted energy being turned into thermal energy (heat). Calculate how much electrical energy must be supplied if 3 J of light energy are to be obtained.
| Data statements | h = 0.02 Eout = 3 J |
2% means 2/100, which as a decimal is 0.02 |
| Formula | h = Eout / Ein | |
| Transposition | Ein = Eout / h | |
| Substitution | Ein = 3 J / 0.02 | |
| Evaluation | Ein = 200 J | 150 has to be rounded up to 1 sig. fig. |