Telescopes (AQA A Level Physics): Exam Questions

State what is meant by normal adjustment when applied to an astronomical refracting telescope.

Which combination of lenses gives the largest angular magnification when used as an astronomical telescope in normal adjustment?

V1031 and WASP-82 are two stars in the constellation Orion.

V1031 appears 40 times brighter than WASP-82 when viewed from Earth. The apparent magnitude of V1031 is 6.0

Calculate the apparent magnitude of WASP-82.

V1031 is just visible to the naked eye of an astronomer when her pupil diameter is 7 mm.

Suggest whether she can observe WASP-82 using a telescope with an objective diameter of 60 mm.

Support your answer with a calculation.

CCDs are often connected to telescopes.

Explain two reasons why this improves the ability of astronomers to observe dim stars.

Draw a ray diagram to show how a converging lens can cause spherical aberration.

Draw a labelled ray diagram for an astronomical refracting telescope in normal adjustment.

Show three non-axial rays passing through both lenses.

Label the principal foci of the lenses.

The James Lick telescope is an astronomical refracting telescope.

When in normal adjustment, the distance between the lenses of the telescope is 17.4 m and the angular magnification is 750.

Calculate the focal length of the eyepiece lens.

The James Lick telescope can be used to identify binary stars.

Two techniques are available using this telescope:

• using a processed image from a CCD, and

• direct observation using the naked eye.

Compare the use of a CCD with the use of the naked eye to observe binary stars with this telescope.

Explain what is meant by the Rayleigh criterion.

A telescope uses wavelengths in the range 90 nm to 120 nm.

Explain why this telescope must be located in space.

Go on to discuss one advantage that this telescope has compared to a telescope with the same aperture that uses visible light.

Table 1 shows information about two telescopes.

Table 1

Each telescope detects radio waves with a wavelength of 21 cm.

Compare the performances of the telescopes in Table 1 when both are used to observe the same faint radio objects.

Draw a ray diagram for a Cassegrain telescope.

Your diagram should show the paths of two rays up to the eyepiece lens.

The rays should initially be parallel to the principal axis.

A spacecraft passes Pluto at a distance of 12 500 km. The telescope on board has an aperture of diameter 0.21 m and operates at a wavelength of 450 nm.

Discuss whether this telescope is suitable for studying a crater with a diameter of approximately 1 km on Pluto.

The Hubble telescope has an aperture of diameter 2.4 m.

Compare the collecting power of the Hubble telescope with the telescope on the spacecraft in part (b).

An astrophysicist had to decide whether to use a reflecting telescope or a refracting telescope on the spacecraft in part (b).

Discuss which type of telescope to use.

State the defining property of a black hole.

In 2019, astronomers linked several radio telescopes to produce a single telescope called the EHT. The resolution of the EHT is the same as the resolution that a telescope with an aperture equal to the diameter of the Earth could achieve.

Table 2 shows data about the EHT and the Hubble telescope.

Table 2

Galaxy M87 is 5.3 × 10⁷ light years from Earth. The supermassive black hole at the centre of M87 has a mass 6.5 × 10⁹ times the mass of the Sun.

The radius of the event horizon is .

The astronomers propose to use either the EHT or the Hubble telescope to observe stars whose distance from the centre of the black hole is less than .

Discuss, with calculations, which telescope is more suitable for this observation.

An astronomer uses an astronomical refracting telescope in normal adjustment to observe a binary star system.

Draw a ray diagram for an astronomical refracting telescope in normal adjustment.

Include in your diagram:

• three non-axial rays

• labelled principal foci for the lenses.

The distance between the lenses of the telescope is 1.20 m. The objective lens has a focal length of 1180 mm.

Calculate the angular magnification of the telescope in normal adjustment.

The astronomer also has access to a reflecting telescope with an objective diameter of .

Each telescope observes the binary system at a wavelength of .

The two stars in the binary system subtend an angle of when viewed by the unaided eye.

The typical human eye has a minimum angular resolution of .

Deduce whether each telescope can resolve the two stars in the binary system. Support your answer with a calculation.

The reflecting telescope has a larger aperture than the refracting telescope.

State one advantage of using the reflecting telescope over the refracting telescope for observing the binary system.