Chapter 12.8, Problem 2E

To determine

To calculate: The illumination that is provided a light giving, from a desk top $3$ m from a $315$ cd lamp.

Answer to Problem 2E

The illumination is: $35$lx.

Explanation of Solution

Given information:

The illumination that is provided a light giving, from a desk top $3$ m from a $315$ cd lamp.

Formula used:

For find the illumination,

  $E=\frac{l}{r^2}$

Calculation:

Consider a surface provided illumination from a desk top $3$ m from a $315$ cd lamp.

Recall that for find the illumination,

  $E=\frac{l}{r^2}$

Here the values are:

  $r=3\text{m,l=315}$

Therefore, the illumination given by,

  $\begin{array}{c}E=\frac{l}{r^2}\\ E=\frac{315}{3^2}\\ E=\frac{315}{9}\\ E=35\end{array}$

Thus, the value of the illumination is $35$ lx.