transmitted-intensity-sets-power-and-pressure - Electromagnetic Waves and Polarization Step by Step

Beam power and absorber pressure close from the same transmitted intensity source. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Transmitted intensity sets beam power

A finite beam power is transmitted intensity times illuminated area.

P = I\,A = 9\ \text{W}/\text{m}^{2}\cdot4\ \text{m}^{2}=36\ \text{W}

An absorber pressure is transmitted intensity over speed

The same transmitted intensity and same speed close pressure and power for absorber

p = \frac{I}{c} = 9\ \text{W}/\text{m}^{2}\cdot \frac{1}{6}\Rightarrow \tfrac{3}{2}\ \text{Pa}