1.

A photoelectric surface is illuminated successively by monochromatic light of wavelength lambda and ( lambda)/(2). If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function at the surface of material is

Answer»

`(HC)/(LAMBDA)`
`(2hc)/(lambda)`
`(hc)/(3lambda)`
`(hc)/(2lambda) `

SOLUTION :`(hc)/(2lambda) `:
`KE_1=(hc)/(lambda)-phi`.............. (1)
` 3KE_1=(2hc)/(lambda)-phi`
` KE_1=(2hc)/(3lambda)-(phi)/(3)`................... (2)
Equating (1) and (2)
`(hc)/(lambda)-phi=(2hc)/(3lambda)-(phi)/(3)`
`(hc)/(3lambda)=(2phi)/(3) implies phi = (hc)/(2lambda)`


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