Homework 4
Due: Thursday, 25th April
Chapter 3 and 4
Show your work when required!
M = fo/fe
c = lambda * frequency
Wien's Law: lambda = 0.0029/T
Stefan-Boltzman Law: F = sigma T^4
Doppler effect: v = c (lambda - lambda0)/lambda0
1. a) Make a sketch of a reflecting and refracting lens. Label the focal length, focus and mark the paths of three light rays. (3 marks)
b) Suppose you buy a 10 cm diameter refracting telescope with a 100 cm objective focal length lens. What magnification do you get with a 25 mm focal length eyepiece lens? Suppose your friend has a 20 cm diameter telescope with a 50 cm objective focal length lens, what magnification would she get with the same eyepiece lens? (2 marks)
c) Which telescope is better for observing faint objects in the night sky?(1 mark)
2. a) If the surface temperature of a star is 2000K, what is the wavelength and frequency of its maximum emission? (2 marks)
b) Would this star look redder or bluer than our sun as viewed from Earth by your unaided eye? (1 mark)
c) A second star has a surface temperature of 8000K. What is the ratio of the wavelengths of maximum emission, lambda(star 1)/lambda(star 2). Answer this using proportionality rather than calculating the wavelength of maximum emission for the second star. (2 marks)
3. a) Calculate the flux emitted from the surface of a star with temperature 5800K and 11600K. (2 marks)
b) If the two stars have the same radius, by what factor is the second star more luminous than the first? Use proportionality for full credit (2 marks)
4. a) A spectrum of a star reveals it has a hydrogen emission line at a wavelength of 629.543 nm but in the laboratory the wavelength of the same hydrogen line is found to be 656.285 nm. Calculate the velocity of this star. (2 marks)
b) Is the star moving toward us or away from us? (1 mark)
5. Sketch the electromagnetic spectrum. Mark on at least 5 different wave bands including the visible part of the spectrum. Indicate which part of the spectrum is blue and which is red. Show which side is long wavelength and which side is short wavelength. (4 marks)
Total 22 marks