The ratio of longest wavelength line in the Balmer andaschen series of hydrogen spectrum is

Options

A. `(5)/(36)`
B. `(7)/(20)`
C. `(7)/(144)`
D. `(5)/(27)`

Answer

B

Explanation

The wavelength of Balmer series is given by
`(1)/(lambda_B)=R[(1)/(2^2)-(1)/(3^2)]=(5)/(36)R ...(i)`
The wavelength for paschen series is given by
`(1)/(lambda_p)=R[(1)/(3^2)-(1)/(4^2)]=(7)/(144)R ...(ii)`
On dividing Eq.(ii) by Eq.(i), we get
`(lambda_B)/(lambda_p)=(7)/(20)`