Let the focal length of the objective and eye lens be 1.2 cm and 3 cm , respectively. Let the object is put 1.25 cm away from the objective lens and the final image is formed at infinity. What is the magnifying power of the microscope?

Question

Let the focal length of the objective and eye lens be 1.2 cm and 3 cm , respectively. Let the object is put 1.25 cm away from the objective lens and the final image is formed at infinity. What is the magnifying power of the microscope? (A) 150 (B) 200 (C) 250 (D) 400

Tardigrade Admin · Accepted Answer

The microscope here, is a compound microscope which is a combination of objective and eyepiece.
For the objective lens,

\frac{1}{f _{o}} = \frac{1}{v _{o}} - \frac{1}{u _{o}}

Objective lens is convex, so

f_{o} = 1.2 c m

\frac{1}{+ 1.2} = \frac{1}{v _{o}} - \frac{1}{( - 1.25 )} \frac{1}{+ 1.2} = \frac{1}{v _{o}} + \frac{1}{1.25} \frac{1}{v _{o}} = \frac{1}{1.2} - \frac{1}{1.25} v_{o} = 30 c m

When final image is at infinity,
Net magnification,

m = m_{o} \times m_{e}

m = \frac{v _{o}}{u _{o}} \times \frac{D}{f _{e}}

m = \frac{30}{- 1.25} \times \frac{25}{3} ∣ m ∣ = 200

Q. Let the focal length of the objective and eye lens be $1.2 c m$ and $3 c m$ , respectively. Let the object is put $1.25 c m$ away from the objective lens and the final image is formed at infinity. What is the magnifying power of the microscope?

$150$

$200$

$250$

$400$

Q. Let the focal length of the objective and eye lens be 1.2cm and 3cm , respectively. Let the object is put 1.25cm away from the objective lens and the final image is formed at infinity. What is the magnifying power of the microscope?

150

200

250

400

Q. Let the focal length of the objective and eye lens be $1.2 c m$ and $3 c m$ , respectively. Let the object is put $1.25 c m$ away from the objective lens and the final image is formed at infinity. What is the magnifying power of the microscope?

$150$

$200$

$250$

$400$