Efficiency is the ratio of output work to input work, expressed as a percentage. Light bulbs put out less light energy than the amount of electrical energy that is put into the bulb.

Question

An illustration of a wide arrow with a light bulb at the tail of it labeled electrical energy 100 J, breaks into a small arrow going forward labeled light 10 J and a larger curling away labeled heat 90 J.
The goal of the bulb is to produce light. What is the efficiency of this bulb as it works to put out light?

10%
80%
90%
100%

Answer 1

To calculate the efficiency of the light bulb in converting electrical energy into light energy, we use the formula for efficiency:

\[ \text{Efficiency} = \left( \frac{\text{Output Work}}{\text{Input Work}} \right) \times 100% \]

In this case, the output work is the light energy produced by the bulb, which is 10 J, and the input work is the electrical energy supplied to the bulb, which is 100 J. Plugging in these values, we get:

\[ \text{Efficiency} = \left( \frac{10 , \text{J}}{100 , \text{J}} \right) \times 100% = 10% \]

Therefore, the efficiency of the bulb in producing light is 10%.