Stars as Black Bodies Flashcards
What is a black body?
An object with a pure black surface that emits radiation strongly and in a well-defined way and absorbs all light incident on it.
Outline the graph of wavelength against power output.
- Black body curves
- Depends on temperature
- Visible wavelengths between about 0.25 and 0.75 micro-metres
- Peak shifts for different curves (shallower curves)
What is the generic definition of a black body?
A black body is a body that absorbs all electromagnetic radiation of all wavelengths and can emit all wavelengths of electromagnetic radiation.
What can we use black body radiation curves for?
Estimating an object’s temperature and other properties.
What is Wien’s displacement law?
All black body spectra have a peak intensity. The wavelength that this peak occurs at is called the peak wavelength. The higher the surface temperature, the shorter the peak wavelength.
What are the general findings of Wien’s law?
A hotter black body will emit more radiation than a cooler one, and it’s peak wavelength will be a shorter wavelength. Also has a higher power output.
What is Stefan’s law?
The power output is proportional to the fourth power of the star’s surface temperature and directly proportional to the surface area.
State an equation for intensity of a star in relation to it’s power output and distance.
I = P / 4πd^2
What is the relationship between distance and intensity of a star?
Inverse square law.
What are the assumptions about a star when using the inverse square law?
The star is spherical and gives out an even amount of power in every direction.
