The velocity of a moving galaxy is `300 kms^(-1)` and th apparent change in wavelength of a spectral line emitted from the galaxy is observed as 0.5 nm. Then, the actual wavelength of the spectral line is

Options

A. 3000Å
B. 5000Å
C. 6000Å
D. 4500Å

Answer

B

Explanation

v = 300 km/s
`v = 300 xx 10^(3) m//s`
`lambda = 0.5 nm`
`= 0.5 xx 10^(-9)m`,
`c = 3 xx 10^(8) m//s`
`therefore (Delta lambda)/(lambda) = (v)/(c)`
`lambda = (Delta lambda c)/(v)`
`= (0.5 xx 10^(-9) xx 3 xx 10^(8))/(300 xx 10^(3))`
`= 5 xx 10^(-7) = 5000 Å`