Single dish radio telescopes, I-R, U-V and X-ray telescopes (A-level only) Flashcards – AQA A-level Physics (7408)

What does a telescope’s angular resolution describe, and what indicates better resolution?

How well it distinguishes two closely spaced sources as separate. A smaller minimum resolvable angular separation means better resolution.

How does the minimum angular separation of a diffraction-limited telescope depend on wavelength and aperture diameter?

$\theta \propto \frac{\lambda}{D}$, where $\lambda$ is wavelength and $D$ is aperture diameter.

Why does a radio telescope need a larger aperture than an optical telescope to achieve comparable angular resolution?

Radio waves have much longer wavelengths than visible light.

What is a telescope’s collecting power?

Its ability to gather incoming radiation.

For the same incident energy flux, how does collecting area affect the energy a telescope receives per unit time?

A larger collecting area receives more energy per unit time.

How does the collecting area of an unobstructed circular aperture depend on its diameter?

It is proportional to the square of the diameter: $A \propto D^2$.

What do radio dishes and optical telescope apertures do with incoming radiation?

They gather it over an area and direct it to a receiver.

How can the collecting powers of radio and optical telescopes be compared?

By comparing their effective collecting areas.

How does collecting more radiation help a telescope detect signals?

It helps the telescope detect weaker signals.

Is collecting power the same as angular resolution?

No. They are distinct telescope properties.