Question

An angular magnification of $30\text{X}$ is desired using an eye piece of focal length $5\text{cm}$ and an objective lens. Find the magnifying power of objective lens. [Given angular magnification is achieved in case of normal adjustment]

• A. $6$
• B. $7$
• C. $8$
• D. $9$

Answer 1

The correct option is A $6$

Given:

$m=30$ and $f_e=5\text{cm}$

We know magnifying power of eyepiece, $m_e=\frac{D}{f_e}$

$\Rightarrow m_e=\frac{25}{5}=5$

Now, we know that total magnification,

$m=m_e\times m_0$

$\Rightarrow 30=5\times m_0$

$\therefore m_0=6$

Hence, $\left(A\right)$ is the correct answer.

Key Concept: Total magnification of a combination of lenses is equal to the product of magnification of individual lenses.