AQA A Level Physics Paper 3 Section B: Astrophysics November 2020 question paper 7408/3BA

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 Question 01.2.

An astrophysicist had to decide whether to use a reflecting telescope or a refracting telescope on the spacecraft in Question 01.2.

Discuss which type of telescope to use.

Table 1 summarises some information about four stars in the constellation Cassiopeia.

Which star has the highest surface temperature? Tick () one box.

Figure 1 shows the intensity received at Earth from two of the stars, plotted against wavelength. The effect of absorption by the Earth’s atmosphere is not shown.

Discuss what information can be found from Figure 1 about the temperature and colour of these stars. Support your answer with suitable calculations.

State which star in Table 1 is dimmest on the absolute magnitude scale.

Calculate the absolute magnitude of Schedar.

Tsih has a mass over 15 times the mass of the Sun. Tsih may eventually collapse to form a black hole.

Calculate the radius of the event horizon for a black hole with a mass 15 times that of the Sun.

Type 1 a supernovae can be used as standard candles.

State what is meant by a standard candle.

Sketch on Figure 2 the light curve for a type 1 a supernova. Annotate your graph with suitable scales and a unit for time.

Measurements of type 1 a supernovae are used to find a value for the Hubble constant.

The distance from Earth is known for many type 1 a supernovae.

Describe how these values of distance are used, with other data, to find the Hubble constant.

Your answer should include:

• the other data needed and how these data are used

• the graph plotted, including appropriate units for the axes

• how the Hubble constant is obtained and any limitations on the result.

Table 2 gives data about the supergiant star Melnick 34 and the Sun.

Discuss why the evolution of a supergiant star in the local part of our galaxy could be dangerous for life on Earth.