Week 4, clip 9

Timepoint:  04:29.6

1) If a star has a luminosity 100 times greater than the Sun, and a temperature that is half (1/2) of the Sun's temperature, how large is its radius in units of the Sun's radius?  Round your answer to two significant digits.

Timepoint:  11:27.5

2) Which of the following star types is most likely to have a temperature of 10,000 K?

- Type B
- Type F
- Type G
- Type M

Answers:
1) [36,44] is the accepted range.

Explanation:
Radius is proportional to the square root of luminosity and to the inverse square of the temperature ( R is proportional to  L^{0.5} T^{-2} ). 

Comparing to the Sun,  R = R_Sun ( 100^{0.5} * 0.5^{-2}) = 40 R_Sun

2) Type B