Astronomical telescope consisting of two converging lenses (A-level only) Flashcards – AQA A-level Physics (7408)

What image does the objective lens of an astronomical telescope form of a distant object?

A real, inverted intermediate image.

In an astronomical telescope, how do rays from one distant object point reach the intermediate image?

They arrive parallel and converge at the corresponding image point.

In normal adjustment, where is the intermediate image relative to the telescope’s two focal planes?

At the objective’s image-side focal plane and the eyepiece’s object-side focal plane.

In normal adjustment, how do rays from each point of the intermediate image emerge from the eyepiece?

They emerge parallel.

Where is the final image of an astronomical telescope in normal adjustment, and what does this mean for the viewer’s eye?

It is at infinity, so it can be viewed by a relaxed eye.

For thin lenses in normal adjustment, what is the separation of a telescope’s objective and eyepiece in terms of their focal lengths?

$f_o + f_e$

How is the final image in an astronomical telescope oriented relative to the object?

It is inverted.

How is the magnitude of a telescope’s angular magnification defined?

The angle subtended by the final image at the eye divided by the angle subtended by the object at the unaided eye.

For an astronomical telescope in normal adjustment, what is the magnitude of angular magnification in terms of objective focal length $f_o$ and eyepiece focal length $f_e$, using the small-angle approximation?

$M = \frac{f_o}{f_e}$