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. decreases
• B. increases
• C. remains constant
• D. first increase and then decreases

Hint:

The focal length is longer for red light, so M = 1 + D/f is smaller.

Answer 1

The Correct Option is A

Step 1: Dispersion:
Blue bends more than red in glass, so $\mu_{blue} > \mu_{red}$.

Step 2: Focal length:
Greater $\mu$ means a stronger lens, so $f_{blue} < f_{red}$.

Step 3: Magnification:
$M = 1 + D/f$ falls as $f$ rises. Changing from blue to red lowers $M$, option (A).

Final Answer:
Magnifying power decreases. \[ \boxed{\text{(A) }\text{decreases}} \]