What primary factor determines the intensity of solar radiation?

• A. Distance from the Sun
• B. Angle of Incidence
• C. Duration of daylight
• D. Earth's rotation speed

Answer: (B)

The primary factor that determines the intensity of solar radiation is the angle of incidence. This refers to the angle at which sunlight strikes the Earth's surface. When the sun's rays hit the surface directly, at a steep angle, the energy is concentrated over a smaller area, resulting in higher intensity solar radiation. Conversely, when sunlight strikes at a shallower angle, the energy is dispersed over a larger area, leading to lower intensity.

While the distance from the Sun does play a role in the amount of solar energy that reaches Earth, it has less influence on the localized intensity of the sunlight experienced in different locations and at different times of the day. Factors such as the duration of daylight and Earth’s rotation speed affect the amount of sunlight received over a cycle but do not directly determine how intense that sunlight is at any given moment. The angle of incidence is therefore the most critical factor in establishing the intensity of solar radiation received at a particular point on the Earth's surface.