Question

You are standing 1.8 m from a 100-w lightbulb. If the pupil of your eye is a circle 5.0 mm in diameter, how much energy enters your eye per second?

Answer 1

The amount of energy that enters your eye per second is 0.02 W.

Step-by-step explanation:

To calculate how much energy enters your eye per second, we need to find the number of photons per second and the energy per photon. Given that the lightbulb emits 500 photons per second and the energy output of the lightbulb is 10% in the visible range, we can calculate:

Total energy per second = Power output of the lightbulb x Energy in visible range
Total energy per second = 100 W x 0.1 = 10 W
Energy per photon = Total energy per second / Total number of photons per second
Energy per photon = 10 W / 500 photons per second = 0.02 W

Therefore, the amount of energy that enters your eye per second is 0.02 W.