Question

question 39
if you are observing two stars which have the same radius, but star a has a peak wavelength of 800 nm & star b has a peak wavelength of 450 nm, what must be true?
star b is larger than star a.
star b is redder & brighter than star a.
star b is bluer & brighter than star a.
star a must be hotter than star b.

Explanation:

According to Wien's displacement law, the peak - wavelength of a black - body (stars can be approximated as black - bodies) is inversely proportional to its temperature ($\lambda_{max}T = b$, where $b$ is Wien's displacement constant). A shorter peak - wavelength indicates a higher temperature. Star B has a shorter peak - wavelength ($450\ nm$) compared to Star A ($800\ nm$), so Star B is hotter. Also, bluer light has shorter wavelengths and redder light has longer wavelengths. Since Star B has a shorter peak - wavelength, it is bluer. And a hotter star of the same size is brighter.

Answer:

Star B is bluer & brighter than Star A.