A monochromatic radiation of wavelength `lambda` is incident on a sample containing `He+`. As a result the Helium sample stars radiating. A part of this radiation is allowed to pass through a sample of atomic hydrogen gas in ground state. It is noticed that the hydrogen sample has stared emitting electrons whose maximum kinetic energy is `37.4 eV`.
`(hc = 12400 eV Å)`. Then `lambda` is

Options

A. `275 Å`
B. `243 Å`
C. `656 Å`
D. `386 Å`

Answer

B

Explanation

Maximum enegry of radiation incident on `H`-sample `=KE_(max)` of electron `+13.6 eV = 51eV` this energy corresponds to the transition `n = 4 rarr n = 1` in Helium for electrons of the He to get excited to `n = 4`
`lambda = (12400)/((51)) = 243 Å`