**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

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 ( n_{1} =
2 ; n_{2} = 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