Black-bodies and Colours

Question 1

What is a black body?

Answer 1

A body that absorbs perfectly at all wavelengths

Question 2

What is Wien’s displacement law?

Answer 2

λ_max T = 2.898 × 10^−3 m K

Question 3

How does the black body curve change at higher T?

Answer 3

The peak shifts to the left and gets more narrow

Question 4

What is the total power per unit area of a black body?

Answer 4

J = σT^4

Question 5

What is the total luminosity of a black body?

Answer 5

P= σAT^4
For spherical P=4πR^2σT^4

Question 6

What is the Stefan-Boltzmann constant?

Answer 6

σ=5.670x10^-8 Wm^-2K^-4

Question 7

What is the luminosity of a star?

Answer 7

L=4πR^2σTeff^4
Where Teff is the temperature at the surface of a star

Question 8

In what order are colour indices written?

Answer 8

With the shorter wavelength first
B-V

Question 9

How does the colour magnitude relate to the colour?

Answer 9

The more negative the colour the more of that colour the object appears
Similar to apparent magnitude

Question 10

What are the colours?

Answer 10

U= Ultraviolet
B= Blue
V= Visible
R= Red
I= Infrared