Question

The focal length of the objective used in compound microscope and telescope is respectively

• A. short and short
• B. large and large
• C. large and short
• D. short and large

Hint:

For magnification in microscopes, a short focal length is used, while for better resolution and distance viewing in telescopes, a large focal length is required.

Answer 1

The Correct Option is D

Step 1: Understanding the focal lengths for different instruments.
The focal length of the objective lens in optical instruments plays a crucial role in determining their magnification and resolving power. - For a compound microscope: The objective lens has a short focal length to allow for a larger magnification. This allows a small object to be magnified by a large amount, making it suitable for observing small details. - For a telescope: The objective lens has a large focal length to provide better resolution and the ability to view distant objects clearly. A larger focal length in a telescope means a higher resolving power and a clearer image over great distances. Step 2: Explanation of the options.
Let's analyze the given options: - (A) short and short: This is incorrect because both the objective lens of a compound microscope and a telescope do not have short focal lengths. - (B) large and large: This is incorrect because while the telescope requires a large focal length, the compound microscope needs a short focal length for high magnification. - (C) large and short: This is incorrect as it suggests that a telescope has a short focal length, which is false. - (D) short and large: Correct. The compound microscope requires a short focal length for the objective lens to magnify small objects, and the telescope requires a large focal length for better resolution over long distances. Step 3: Conclusion.
The correct answer is (D) short and large. The focal length of the objective in a compound microscope is short, and in a telescope, it is large.