Q. The current in a photoelectric cell can be just reduced to zero by a
potential of 1.8 volts when light of wavelength 2200 A'is incident on
the cathode. Find the photoelectric work function of the cathode.
(h = 6.63 x 10-34.Js, c = 3 x 108ms), 1 eV = 1.6 x 10-19.J, e = 1.6 x 10-19 C)
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Explanation:
Given : e=1.6×10
−19
C, c=3×10
8
m/s
ϕ=4.2eV, h=6.63×10
−34
J.s, V
S
=3V
ϕ=4.2×1.6×10
−19
J
=6.72×10
−19
J
(a) Threshold wavelength =λ
0
=
ϕ
hc
=
6.72×10
−19
6.63×10
−34
×3×10
8
=2.960×10
−7
m
=2960
A
˚
(b) Maximum kinetic energy,
KE
max
=eV
S
=1.6×10
−19
×3
=4.8×10
−19
J
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