Question

If the focal lengths of objective and eye lens of a microscope are 1.2 cm and 3 cm respectively and the object is put 1.25 cm away from the objective lens and the final image is formed at infinity, then magnifying power of the microscope is

• A. 150
• B. 200
• C. 250
• D. 400

Answer 1

Answer: (B)

200

Answer 2

Given that $f_{o} = 1.2cm$, $f_{e} = 3cm$, $u_{o} = 1.25cm$

By using $m_{\infty} = - \frac{f_{o}}{(u_{o} - f_{o})} \cdot \frac{D}{f_{e}}$

⇒ $m_{\infty} = - \frac{1.2}{(1.25 - 1.2)} \times \frac{25}{3} = - 200$.