2.Material&Star

Question 1

What is meant by a black body? [1]

Answer 1

[A body with a surface that] absorbs all radiation[accept: ‘light’] falling upon it.

Question 2

(ii) Suggest why the actual emitted power will, in fact, be more than this calculated. [1]

Answer 2

Absorption / scattering [of radiation by interstellar dust / gas]

Question 3

Dark lines are seen crossing the continuous spectrum of a star. Explain how these lines arise. [3]

Answer 3

Atoms / ion / [accept molecules]of a star’s atmosphere (1)

[or interstellar space or Earth’s atmosphere] absorb specificλ wavelengths (1)

[from the continuous spectrum] promoting electrons to higher energy level (1) [or re-emitting in all directions]

Question 4

What does the author mean by “We can also measure the centripetal acceleration, a, of maser clouds by observing how the Doppler shift velocity changes over time”? (See paragraph 9.) [3]

Answer 4

Measure the velocity using Doppler shift or use of Doppler equation (1)

at different times (1)

acceleration = rate of change of velocity (1) Alternative: Measure the velocity using Doppler shift (1) Obtain v_max (1) v²max/r=a or equivalent e.g. use v and r to calculate a (1)