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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