Question

Suppose that you'd like to find out if a distant star is moving relative to the earth. The star is much too far away to detect any change in its brightness as it moves toward or away from the earth. Instead we can use the Doppler effect to determine its relative speed. For this problem we are going to look at the spectral lines from hydrogen, specifically the one with a wavelength of 656.46 nm.
Required:
What is V(star) , the speed at which the star is moving relative to the earth?

Answer 1

Answer:

The speed will be "18km/s". A further explanation is given below.

Explanation:

According to the question, the values are:

Wavelength,

$\lambda = 656.46 \ nm$

$\Delta \lambda = 0.04$

$c=3\times 10^8$

As we know,

⇒  $\frac{\Delta \lambda}{\lambda} =\frac{v}{c}$

On substituting the values, we get

⇒  $\frac{656.46}{0.04} =\frac{v}{3\times 10^8}$

⇒         $v=\frac{656.46}{0.04} (3\times 10^8)$

⇒            $=16411.5\times 3\times 10^8$

⇒            $=18280 \ m/s$

or,

⇒            $=18 \ km/s$