Question

A spectral line from a star is observed to have a wavelength of 656.5 nm. The rest wavelength of this line is 656.8 nm. (a) What is the speed of the star, and (b) is it approaching or receding from the Earth? (c) If the star’s emitted wavelength is the same as the rest value, what is happening?

Answer 1

speed of star is 1.37 ×
`10^(5)` m/s

it is approaching to earth because wavelength of star is decreasing than rest

if emit same wavelength it does not move anywhere

it will remain steady condition with respect earth

Step-by-step explanation:

given data

wavelength = 656.5 nm

rest wavelength = 656.8 nm

to find out

the speed of the star , is it approaching

solution

we know here equation that is

wavelength shift / wavelength at rest = velocity of source / speed of light

so put all value and find

velocity of source = 3 ×
`10^(-9)` × 3 ×
`10^(8)` / 656.8 ×
`10^(-9)`

velocity of source star = 1.37 ×
`10^(5)` m/s

and

it is approaching to earth because wavelength of star is decreasing than rest

and

if emit same wavelength it does not move anywhere

it will remain steady condition with respect earth