A star moves away from the earh at a speed of 0.8 c while emitting light of frequency ` 6 xx 10^(14) Hz `. What frequency will be observed on the earth ( in units of ` 10^(14)`Hz) ? ( c=speed of light )

Options

A. 0.24
B. 1.2
C. 30
D. 3.3

Answer

B

Explanation

Apparent (observed) frequency, `v'=v(1-(v)/(c))`
`:. v'=6 xx 10^(14)(1-(0.8c)/(c))`
`=6 xx 10^(14) xx 0.2 =1.2 xx 10^(14) Hz `
`:.` In units of `10^(14) Hz `, v'=1.2