Question

In: Physics

White light (ranging in wavelengths from 380 to 750 nm) is incident on a metal with...

White light (ranging in wavelengths from 380 to 750 nm) is incident on a metal with work function Wo = 2.68 eV.

1. For what range of wavelengths (from lmin to lmax) will NO electrons be emitted?

a) Imin=

b) Imax=

Solutions

Expert Solution

Einstein's Photoelectric equation, explain that a part of energy of photon ( hv) is used in liberating the electron from metal surface which is equal to work function (@0 ) .Rest part of energy of photon providing maximum kinetic energy ( 1/2*m*v2 ) to photon. It is given as:

hv = @0 + 1/2*m*v2max

hv ( frequency) = Energy of photon,                    @0 = work function.            K.E = 1/2*m*v2

Electron emission will stop when bombarding photon has energy less than the work function.

So @0 = hv

v = @0 / h

v = 2.68*1.6*10-19 J / 6.63*10-34 J-s

v = 6.467*1014 hz

From ,        c = v*lambda                         ( by velocity ( c) = frequency (v) *wavelength (lambda) )

lambda = c / v

          = 3*108 / 6.467*1014 = 463.8 nm

This refers to lmin = 463 nm where electron leaves with zero K.E

At any wavelength less than 463 nm no electron will be emitted.

Maximun wavelength = 750 nm is given in Q.

so No electron emission with lambda between 463 nm- 750 nm

lmin = 463 nm

lmax = 750nm


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