Dr. I.
Fernini
Special Topics
ASTROPHYSICS (Phys 493)
Fall 2003
Homework 2
Due: October 18
Problem 1:
(a)
At
peak
wavelength at which the surface emits at
(b)
Calculate the energy output per
square meter of the surface at
Problem 2:
The Earth, Venus, and Mars all have carbon dioxide in their atmospheres. Find the ratio of the root mean square speed to escape velocity for each.
Make a statement about the retention of carbon dioxide for these planets.
Problem 3:
In discussing the Coriolis effect, we mentioned that a body, which undergoes acceleration a, will travel a distance s=1/2 at2 in a time t.
Show that the speed of the body is proportional to time and that the body’s acceleration is indeed a.
Problem 4:
(a) What is the energy of one photon of wavelength l = 300 nm? Express your answer both in
joules and in electron volts.
(b) An atom in the second excited state ( n = 3 ) of hydrogen is just barely ionized when a photon
strikes the atom. What is the wavelength of the photon if all its energy is transferred to the
atom?
Problem 5:
(a) How much more energy is emitted by a star at 50,000 K than one at 20,000 K.
(b) What is the predominant color of each star in part (a) ? Use the Wien displacement law and
express your answer in wavelengths.
Problem 6:
At what wavelengths will the following spectral line be observed:
(a) the H-alpha line ( n1 = 2 ; n2 = 3) emitted by a star moving toward us at 500
km/s
(b) the Ca II line (undisplaced wavelength of 397.0 nm) emitted by a galaxy
receding at 20,000 km/s
