The `6000Å` line emitted by a gaseous element in a star iis found to have red shift of ` 15Å`. What is the speed with which the star is receding from the earth ? `(c=3 xx 10^(8) m//s )`

Options

A. `5xx10^(5) m//s `
B. `6xx10^(5) m//s `
C. `7.5xx10^(5) m//s `
D. `9xx10^(5) m//s `

Answer

C

Explanation

The wavelength shift ( Red shift ) `Delta lambda` is given by
` Delta lambda=((v)/(c))lambda `
`:.""v=c((Delta lambda)/(lambda))=3 xx 10^(8) xx (15 xx 10^(-10))/(6000 xx 10^(-10))`
`:. ""v=(45xx10^(8))/(6 xx 10^(3))=7.5xx10^(5) m//s `