If the beam cross-sectional area increases while power remains constant, intensity will?

If the beam cross-sectional area increases while power remains constant, intensity will?

• A. Increase
• B. Decrease
• C. Remain the same
• D. Fluctuate

Answer: (B)

Intensity is the power per unit area, so it changes as the area changes for a fixed power. Since I = P/A, increasing the cross-sectional area while keeping power the same spreads the same energy over more area, reducing the energy flux per unit area. Therefore, intensity decreases. For example, with P = 100 W, expanding the area from 1 m^2 to 4 m^2 drops intensity from 100 W/m^2 to 25 W/m^2. The other possibilities would require changing power or area in different ways, but with a simple area increase and constant power, the intensity must fall.

Intensity is the power per unit area, so it changes as the area changes for a fixed power. Since I = P/A, increasing the cross-sectional area while keeping power the same spreads the same energy over more area, reducing the energy flux per unit area. Therefore, intensity decreases. For example, with P = 100 W, expanding the area from 1 m^2 to 4 m^2 drops intensity from 100 W/m^2 to 25 W/m^2. The other possibilities would require changing power or area in different ways, but with a simple area increase and constant power, the intensity must fall.