What is the wavelength of light emitted when the electron of a hydrogen atom undergoes a transition from an energy level with `n= 4` to an energy level with `n = 2` ? What is the colour corresponding to this wavelength?

Explanation

According to Balmer formula,
Wave number `(bar(v))=R_(H)[(1)/(n_(1)^(2))-(1)/(_(2)^(2))]cm^(-1) , n_(1)-2, n_(2)=4, R_(H)=109678cm^(-1)`
`:. " " bar(v)=109678 [(1)/(2^(2))-(1)/(4^(2))]cm^(-1)=(109678xx3)/(16) cm^(-1)`
`lambda=(1)/(bar(v))=(16)/(109678xx3)cm=(16xx10^(7))/(109678xx3)nm=486 nm`