Question

Two different lenses are used in telescope because

• A. Magnification is increased
• B. Focal length is increased
• C. More light is captured
• D. Spherical aberration is increased

Answer 1

The Correct Option is A

To understand why two different lenses are used in a telescope, it's essential to grasp how a telescope functions. A basic telescope is composed of an objective lens and an eyepiece lens. The primary purpose of the telescope is to collect more light than the human eye and magnify distant objects, making them visible with better clarity.

1. Objective Lens: The objective lens is the large lens at the front of the telescope. Its primary job is to capture as much light as possible and focus it to form an image.
2. Eyepiece Lens: The eyepiece lens is smaller and located at the back of the telescope. It magnifies the image formed by the objective lens for detailed viewing.

By using two different lenses, the telescope can increase its magnification. The magnification of a telescope is defined as the ratio of the focal length of the objective lens to the focal length of the eyepiece lens:

\(Magnification = \frac{F_{\text{objective}}}{F_{\text{eyepiece}}}\)

Here's why the correct answer is "Magnification is increased":

• Using lenses with different focal lengths allows telescopes to have variable magnification, which is critical for observing objects at different distances.
• An increased focal length of the objective lens enhances the ability to gather light, creating a brighter image that can be magnified by the eyepiece lens.

Let's evaluate the other options:

• Focal length is increased: While different focal lengths contribute to magnification, the goal is specifically to increase magnification rather than just focal length.
• More light is captured: This is primarily determined by the aperture (size) of the objective lens, not solely by using different lenses.
• Spherical aberration is increased: Spherical aberration is a lens defect, generally reduced by using high-quality lenses, and is not a desired effect.

In conclusion, the primary reason for using two different lenses in a telescope is to increase magnification, allowing observers to view distant celestial objects clearly.