Chapter 12.8, Problem 4E

To determine

To calculate: The illumination that is provided a lamp form the distance $2$ m is $120$ cd lamp.

Answer to Problem 4E

The illumination is: $35$lx.

Explanation of Solution

Given information:

The illumination provided a lamp form the distance $2$ m is $120$ cd lamp.

Formula used:

For find the illumination,

  $E=\frac{l}{r^2}$

Calculation:

Consider a surface provided illumination form the distance $2$ m is $120$ cd lamp.

Recall that for find the illumination,

  $E=\frac{l}{r^2}$

Here the values are:

  $r=2\text{m,l=120}$ cd

Therefore, the illumination given by,

  $\begin{array}{c}E=\frac{l}{r^2}\\ E=\frac{120}{4^2}\\ E=\frac{120}{4}\\ E=30\end{array}$

Thus, the value of the illumination is $30$ lx.