Question

A postage stamp appears raised by 7.0 mm, when placed under a rectangular glass block with a refractive index 1.5. Find the thickness of the glass block.

Answer 1

Step 1: Given data
Normal shift or raised by$=7.0mm$, refractive index $\mu =1.5$
Step 2: Formula used
Normal shift or raised $=t(1-1/\mu )$
where $\mu$-refractive index, $t-$thickness of glass
Step 3: Calculation
Let t be the thickness of the slab
We know that:
Normal shift or raised $=t(1-1/\mu )$

$$\begin{gathered} 7=t(1-10/15) \\ 7=t\left(\frac{15-10}{15}\right) \\ 7=t\left(\frac{5}{15}\right) \\ 7=t\left(\frac{1}{3}\right) \end{gathered}$$

$t=21mm$
Hence, the thickness of glass is $21mm$.