Question

A lightbulb uses 330,000 Joules in an hour. The bulb emits 30,200 Joules of light energy and 299,800 Joules of thermal energy. What is the lightbulb's efficiency? (1 point)

8%

0.92%

90.8%

9.15%

Answer 1

To calculate the efficiency of the lightbulb, we can use the formula:

\[
\text{Efficiency} = \left( \frac{\text{Useful energy output}}{\text{Total energy input}} \right) \times 100
\]

In this case, the useful energy output is the light energy emitted by the bulb, which is 30,200 Joules, and the total energy input is 330,000 Joules.

Now we can plug in the values:

\[
\text{Efficiency} = \left( \frac{30,200 \text{ Joules}}{330,000 \text{ Joules}} \right) \times 100
\]

Calculating the fraction:

\[
\frac{30,200}{330,000} \approx 0.09151515
\]

Now multiply by 100 to express it as a percentage:

\[
\text{Efficiency} \approx 0.09151515 \times 100 \approx 9.15\%
\]

Thus, the lightbulb's efficiency is **9.15%**.