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Manipal Entrance Test 2015 Physics Paper
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© examsnet.com
Question : 42
Total: 50
Find the frequency of light which ejects electron from a metal surface fully stopped by a retarding potential of 3V. The photoelectric effect begins in this metal at a frequency of
6
×
10
15
Hz
1.324
×
10
15
Hz
2.295
×
10
16
Hz
3.678
×
10
18
Hz
2.7
×
10
14
Hz
Validate
Solution:
According to Einstein’s photoelectric equation,
E = hv - w
If
V
s
is retarding or stopping potential and
v
0
is the threshold frequency, then the above equation becomes
e
V
s
=
h
v
−
h
v
0
h
v
=
e
V
s
+
h
v
0
v
=
e
V
s
h
+
v
0
Hence,
e
=
1.6
×
10
−
19
C
V
s
=
3
V
,
v
0
=
6
×
10
−
14
Hz
Therefore, required frequency,
v
=
1.6
×
10
−
19
×
3
6.63
×
10
−
34
+
6
×
10
14
=
1.323
×
10
15
Hz
© examsnet.com
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