PROBLEM SET  #3

Some work with the nature of light ---

ASTR 1110

Think each problem through, and present your logic.

1. What is the frequency of a "dental" x-ray having a wavelength of 0.1?  What is its energy? (Note 1Å=0.1nm)

2. The star Zeta Puppis has a temperature of 30,000K.  At what wavelength is it brightest?

3. The Earth has a temperature of 300K. Jupiter is 5AU from the Sun. Estimate the temperature of Jupiter in the following way.  First, use the inverse square law to estimate what factor lower the sunlight flux per square centimeter is on Jupiter.  This means that T4 must be lower by this factor because of the Stefan-Boltzmann Law. Take the fourth root of the flux factor and divide it into the Earth's temperature to estimate Jupiter's temperature.

4. A radio transmitter on a spacecraft emits a signal at a frequency of 108Hz.  At Earth the signal is received and noted to be at 99,970,000Hz. How fast is the spacecraft moving?  Is it receding or approaching?