1 ) Initially a photon of wavelength λ1 falls on photocathode and emits an electron of maximum energy E1 . If the wavelength of incident photon is changed to λ2 . The maximum energy of the electron emitted becomes E2 . The value of “ hc ” is ?

1 ) Initially a photon of wavelength  λ1 falls on photocathode and emits an electron of maximum energy E1 .  If the wavelength of incident photon is changed to λ2 .  The maximum energy of the electron emitted becomes E2 .  The value of “ hc ” is : -

Solution : -

We know that electron with maximum energy has an energy of

E = ( hc / λ ) – Φ .

∴  Φ = work function of metal .

So ,  E1 = ( hc / λ1 ) – Φ   and    E2 = ( hc / λ2 ) – Φ .

So , subtracting E2 from E1 : -

E1 – E2  =  hc ( 1 / λ1  -   1 / λ2 ) .

So ,

hc = λ1 λ2  x  ( E1 – E2 ) / ( λ1 - λ2 )  ,  Answer .

 

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2 ) A U-235 nuclear reactor generates energy at a rate of  3.70 x 10 ^ 7  j / s .  Each fission liberates 185 MeV useful energy .  If the reactor has to operate for  144 x 10 ^ 4  secs ,  then mass of fuel needed ?

Solution : -

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