Question

The intensity of electromagnetic waves from the sun is 1.4 kW/m2 just above the earth's atmosphere. Eighty percent of this reaches the surface at noon on a clear summer day. Suppose you model your back as a 28 cm × 47 cm rectangle.

Part A How many joules of solar energy fall on your back as you work on your tan for 1.0 h ?

Answer 1

Intensity of electromagnetic waves from the Sun just above the Earth's atmosphere = I₀ = 1.4 kW/m²

Intensity at the surface of Earth at noon on a clear summer day = I

Only 80% of the intensity above the Earth's atmosphere reaches the surface at noon on a clear summer day.

I = 1.12 kW/m²

I = 1120 W/m²

Area of your back = A = 28cm x 47cm = 1316 cm² = 0.1316 m²

Time period you work on your tan = T = 1 hour = 3600 sec

Solar energy falling on your back during your tan = E

E = IAT

E = (1120)(0.1316)(3600)

E = 5.31 x 10⁵ J

A) Solar energy falling on your back during your tan = 5.31 x 10⁵ J