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KVPY 2020-21 SB SX Exam Previous Papers
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© examsnet.com
Question : 39
Total: 120
A zinc ball of radius, R = 1 cm charged to a potential –0.5 V. The ball is illuminated by a monochromatic ultraviolet (UV) light with a wavelength 290 nm. The photoelectric threshold for zinc is 332 nm. The potential of ball after a prolonged exposure to the UV is
–0.5 V
0 V
0.54 V
0.79 V
Validate
Solution:
ϕ
=
12431
3320
=
3.74
e
V
ε
=
h
c
λ
=
12431
2900
=
4.28
e
V
(
K
E
)
max
=
4.28
−
3.74
=
0.54
e
V
Initially sphere is negatively charged so
e
−
will go easily then potential becomes
O
. After that as
e
−
will leave the potential will increase till it reaches the stopping potential value,
V
0
e
V
0
=
0.54
e
V
V
0
=
0.54
V
© examsnet.com
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