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

` Delta E =E_4 - E_2 = (-13.6)/(4^2) - ( - ( 13. 6)/2^2) ( therefore E_n= (E_1)/(n^2))`
` Delta E= ( + 13. 6 xx 3)/( 16) eV`
` therefore (12375)/(lambda) = (13. 6 xx 3)/(16)`
` ( lambda "in " Å )`
`therefore lambda = 4852 Å = 485.2 nm`.