Question 18M.3.SL.TZ2.b.i

A student carries out an experiment to determine the variation of intensity of the light with distance from a point light source. The light source is at the centre of a transparent spherical cover of radius C. The student measures the distance x from the surface of the cover to a sensor that measures the intensity I of the light.

The light source emits radiation with a constant power P and all of this radiation is transmitted through the cover. The relationship between I and x is given by

$$I=\frac{P}{4\pi {(C+x)}^2}$$

The student obtains a set of data and uses this to plot a graph of the variation of $\frac{1}{\sqrt{I}}$ with x.