A beam's power divided by its area equals what quantity?

A beam's power divided by its area equals what quantity?

• A. Power
• B. Pressure
• C. Intensity
• D. Amplitude

Answer: (C)

The main idea is that power is energy per unit time, and when you spread that energy over an area, you get energy per unit area per unit time. That is intensity (often called irradiance in radiometry). So I = P / A. If you keep the total power the same but increase the area, the beam’s intensity drops because the energy is spread thinner. If you decrease the area, the intensity rises. This isn’t about force (that would be pressure, which is force per area) and it’s not about amplitude (a wave’s size), or the total power itself (which doesn’t account for how that power is distributed over area).

The main idea is that power is energy per unit time, and when you spread that energy over an area, you get energy per unit area per unit time. That is intensity (often called irradiance in radiometry). So I = P / A.

If you keep the total power the same but increase the area, the beam’s intensity drops because the energy is spread thinner. If you decrease the area, the intensity rises. This isn’t about force (that would be pressure, which is force per area) and it’s not about amplitude (a wave’s size), or the total power itself (which doesn’t account for how that power is distributed over area).