Question

A simple microscope is used to see the object first in blue light and then in red light. Due to the change from blue to red light, what is the effect on its magnifying power?

• A. Magnifying power increases.
• B. Magnifying power decreases.
• C. Magnifying power is independent of colour of light.
• D. Magnifying power remains constant.

Hint:

Magnifying power is inversely proportional to focal length, which increases with wavelength.

Answer 1

The Correct Option is B

Step 1: Magnifying power of simple microscope.
The magnifying power is given by:
\[ M = \frac{1}{f} \] where $f$ is the focal length.

Step 2: Focal length in different lights.
The focal length is related to the wavelength of light:
\[ f \propto \lambda \]
Step 3: Effect of change in wavelength.
Since red light has a longer wavelength than blue light, the focal length will increase for red light.
This leads to a decrease in magnifying power.

Step 4: Conclusion.
The magnifying power decreases when changing from blue to red light.