Chapter 16, Problem 3STP

To determine

To Choose: The correct option.

Answer to Problem 3STP

D. $1.1\times {10}^3\text{lm}$

Explanation of Solution

Given:

The power of the lightbulb, $\text{Power}=60.0\text{}\text{W}$

The illuminance due to the bulb, $E=9.35\text{}\text{lx}$

The distance at which illuminance is given, $d=3.0\text{}\text{m}$

Formula used:

The illuminance of a source at a distance $r$ is given by,

  $E=\frac{P}{4\pi r^2}$

Where, P is the luminous flux of the source.

Calculation:

Using the given values in above formula, the total luminous flux of the lightbulb will be,

  $\begin{array}{l}E=\frac{P}{4\pi r^2}\\ 9.35=\frac{P}{4\pi {\left(3.0\right)}^2}\\ P\approx 1.1\times {10}^3\text{lm}\end{array}$

Conclusion:

Hence, the total luminous flux of the lightbulb is $1.1\times {10}^3\text{lm}$ .