- Trending Categories
- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies

- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who

**(a)** Draw a labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab. **(b)** Calculate the refractive index of the material of a glass slab. Given that the speed of light through the glass slab is 2 x 10^{8} m/s and in air is 3 x 10^{8} m/s.**(c)** Calculate the focal length of a lens, if its power is â€“ 2Â·5 D.

(a) Labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab is given below:

**
**

**(b) Given:**

The speed of light through the glass slab = $2\times {10^8m/s}$

The speed of light in air = $3\times {10^8m/s}$

**To find: **Refractive index of the material of a glass slab, $n_{ga}$.

**Solution:**

We know that the formula of refractive index $(n)$ is given as-

$Refractive\ index\ of\ a\ medium=\frac {Speed\ of\ light\ in\ vacuum/air}{Speed\ of\ light\ in\ medium}$

Here,

$n_{ga}=\frac {Speed\ of\ light\ in\ air}{Speed\ of\ light\ in\ glass}$

Putting the given values in the expression we get-

$n_{ga}=\frac {3\times {10^8m/s}}{2\times {10^8m/s}}$

$n_{ga}=\frac {3}{2}$

$n_{ga}=1.5$

Thus, the refractive index of the material of a glass slab, $n_{ga}$ is** 1.5.**

(c) Given:

Power of the lens, $P$ = $-$2.5 D

**To find:** Focal length, $f$.

**
Solution:**

We know that formula for power of lens is given as-

$P=\frac {1}{f}$

Putting the value of $f$ in the formula, we get-

$-2.5=\frac {1}{f}$

$f=-\frac {1}{2.5}$

$f=-\frac {10}{25}$

$f=-0.4m$

Thus, the focal length, $f$ of the lens is **-4m.**