### Homework #6

Nature of Light
Due 5pm Friday Oct 17

1. [2 pts]
Solids and opaque hot gases (like stars) emit raditation whose spectrum depends upon temperature. This radiation is called blackbody emission, and is described in more detail at this website. Use the Website to answer the following questions:

• Keep the 'red' bar at 3000K, and gradually increase the temperature in the blue bar. The spectrum shown has short wavelengths (bluer) to the left, and long wavelengths (redder) to the right. In which direction does the peak move as the temperature increases?
• Now move the red bar to a higher temperature than that of the blue bar. Is the red spectrum higher everywhere than the blue one? Are the shapes the same between the red plot and the blue plot?
• Click the mouse button at the peak of the curve and read off the x-value. This is the wavelength of the peak. Plot the position of the peak of the curve against the temperature. Can you find a mathematical relationship between the two?
• Click the Red, Blue, and Visual boxes. The vertical lines show the blue, green, and red regions of the spectrum. Put the temperature bar at 5800K, the temperature of the Sun. What color does the Sun emit most of its light? Now put the temperature at 10,000K. What region of the spectrum is most of the light emitted now? Note that the ratio of red/green/blue is what your eye perceives as color. Hence, the hotter the star, the bluer the color.

2. [1 pt apiece; 6 pts total]
Discuss questions 3, 4, 5, 6, 8, and 10 on page 169 in Trefil and Hazen. Write a short paragraph on each item. You may discuss these questions in groups, but the wording of the writeup should be your own.

3. [2 pts]
Examine the colors on resources page with the spectrometer provided in class. Carefully draw the spectrum for each color and for a lightbulb. Note if the spectrum of each is emission, absorption, continuum, or a combination.