A 60-W light bulb emits spherical electromagnetic waves uniformly in all directions.If 50% of the power input to such a light bulb is emitted as electromagnetic radiation,what is the radiation pressure at a distance of 2.0 m from the light bulb?
A)50 nPa
B)2.0 nPa
C)8.0 nPa
D)16 nPa
E)4.0 nPa

Question

Quizplus · Accepted Answer

The radiation pressure $P$ can be calculated using the formula $P = \frac{I}{c}$, where $I$ is the intensity of the wave and $c$ is the speed of light. Given that 50% of the power (60 W) is emitted as electromagnetic radiation, the effective power is 30 W. The intensity $I$ at a distance $r$ from a point source is given by $I = \frac{P}{4\pi r^2}$. Substituting the given values, $I = \frac{30}{4\pi (2)^2}$ and then calculating $P$ yields a value close to 2.0 nPa.

A 60-W Light Bulb Emits Spherical Electromagnetic Waves Uniformly in All