Question

A star is moving towards the earth with a speed of $4.5\times {10}^{6}m/s$. If the true wavelength of a certain line in the spectrum received from the star is $5890\stackrel{\circ }{A}$, its apparent wavelength will be about _____. $[C=3\times {10}^{8}m/s]$. Ignore the relativistic effects.

• A. $5890\stackrel{\circ }{A}$
• B. $5978\stackrel{\circ }{A}$
• C. $5802\stackrel{\circ }{A}$
• D. $5896\stackrel{\circ }{A}$

Answer 1

The correct option is C $5802\stackrel{\circ }{A}$

Apparent wavelength ${\lambda }^{{}^{\prime }}=\lambda [1-\frac{v}{C}]$

${\lambda }^{{}^{\prime }}=5890[1-\frac{4.5\times {10}^6}{3\times {10}^8}]=5802\stackrel{\circ }{A}$