Question

A 250 watt bulb emits monochromatic light wavelength 198.78 nm. How many photons are emitted by the bulb per second?

Hint:

Look for mathematical simplifications before doing raw arithmetic. Values like $198.78$ in a physics/chemistry problem are almost always chosen specifically to cancel cleanly with combinations of fundamental constants like $h$ and $c$ ($6.626 \times 3 = 19.878$).

Answer 1