Doppler shifted hydrogen absorption lines are seen in the spectrum of a star.
The hydrogen line at 656.28 nm is seen to be shifted to 656.08 nm.
How fast is the star moving (Note: The speed of light is approximately 300,000 km/s, or 3 × 105
km/s.)?
10)____
A) about 1,000 km/s
B) about 1,000,000 km/s
C) about 100 km/s
D) about 10,000 km/s

Respuesta :

Answer:

Explanation:

It is given that,

Wavelength of hydrogen line, [tex]\lambda=656.28\ nm=656.28\times 10^{-9}\ m[/tex]

Shift in wavelength, [tex]\lambda'=656.08\ nm=656.08\times 10^{-9}\ m[/tex]

According to Relativistic Doppler Effect, the shift in wavelength is given by :

[tex]\dfrac{\lambda'}{\lambda}=\sqrt{\dfrac{1+v/c}{1-v/c}}[/tex]

v is the speed of star

c is the speed of light

[tex](\dfrac{\lambda'}{\lambda})^2=\dfrac{c+v}{c-v}[/tex]

[tex]v=c-\dfrac{2c}{(\dfrac{\lambda'}{\lambda})^2+1}[/tex]

[tex]v=3\times 10^8-\dfrac{2\times 3\times 10^8}{(\dfrac{656.08\times 10^{-9}}{656.28\times 10^{-9}})^2+1}[/tex]

[tex]v=91438.32\ m/s[/tex]

or

v = 91.43 km/s

So, the star is moving with a speed of about 100 km/s. Hence, this is the required solution.