What two types of lenses make up an astronomical refracting telescope in normal adjustment?

Two converging lenses: an objective lens and an eyepiece lens.

How are the objective and eyepiece lenses positioned relative to each other in a telescope in normal adjustment?

They are arranged so that the focal point of the objective lens coincides with the focal point of the eyepiece lens.

Why is viewing through a telescope in normal adjustment comfortable for the eye?

Because the final image is at infinity, so the eye is relaxed when viewing.

Describe the nature of the image formed by the objective lens of an astronomical telescope.

A real, inverted, diminished image.

AQA A-Level Physics 7408

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Astrophysics

Astronomical telescope consisting of two converging lenses

4 things to know
Paper 3, section B

Overview

The ray diagram in normal adjustment, and calculating angular magnification from the two focal lengths.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How is angular magnification calculated, why is the objective's focal length long, and how should the eyepiece change to raise magnification?

Process

Where do rays converge in a telescope in normal adjustment, and how do they arrive?

Process

How do rays leave the eyepiece, where must the intermediate image sit, and what kind of image does the objective form?

Key term

Why does the eyepiece lens have a short focal length?

Questions from this subtopic

Each one with the model answer underneath.

1
What two types of lenses make up an astronomical refracting telescope in normal adjustment?
Model answer
Two converging lenses: an objective lens and an eyepiece lens.
2
How are the objective and eyepiece lenses positioned relative to each other in a telescope in normal adjustment?
Model answer
They are arranged so that the focal point of the objective lens coincides with the focal point of the eyepiece lens.
3
Where is the final image formed when an astronomical telescope is in normal adjustment?
Model answer
At infinity.
4
Why is viewing through a telescope in normal adjustment comfortable for the eye?
Model answer
Because the final image is at infinity, so the eye is relaxed when viewing.
5
Describe the nature of the image formed by the objective lens of an astronomical telescope.
Model answer
A real, inverted, diminished image.
6
Where does the objective lens form its image of a distant object?
Model answer
At its focal point.

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