Answer
See answers.
Work Step by Step
Assume the light energy is all absorbed, which leads us to equation 22–10a for radiation pressure. Assume that radiation is emitted uniformly in all directions, so the intensity is the bulb’s power divided by the spherical surface area.
$$Pressure=\frac{\overline{I}}{c}=\frac{25W/(4\pi (0.095m)^2)}{3.00\times10^8m/s}=7.3\times10^{-7}N/m^2$$
The force on your fingertip is the pressure multiplied by your fingertip’s area, which we approximate to be a square centimeter.
$$F=PA=(7.348\times10^{-7}N/m^2)(0.01m)^2=7.3\times10^{-11}N$$
This is an imperceptible force .
