Light with an energy flux of `18 W//cm^2` falls on a non-reflecting surface at normal incidence. If the surface has an area of `20 cm^2`, find the average force exerted on the surface during a `30` minute time span.

Explanation

To solve the problem step by step, we will follow these calculations:

### Step 1: Calculate the total energy incident on the surface.
The energy flux (intensity) is given as \( I = 18 \, \text{W/cm}^2 \). The area of the surface is \( A = 20 \, \text{cm}^2 \). The time duration is \( t = 30 \, \text{minutes} \).

First, convert the time from minutes to seconds:
\[
t = 30 \, \text{minutes} \times 60 \, \text{seconds/minute} = 1800 \, \text{seconds}
...