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JEE Advanced 2021 Paper 2
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© examsnet.com
Question : 19
Total: 57
In a photoemission experiment, the maximum kinetic energies of photoelectrons from metals
P
,
Q
and
R
are
E
P
,
E
Q
and
E
R
, respectively, and they are related by
E
P
=
2
E
Q
=
2
E
R
*
. In this experiment, the same source of monochromatic light is used for metals
P
and
Q
while a different source of monochromatic light is used for the metal
R
. The work functions for metals
P
,
Q
and
R
are
4.0
e
V
,
4.5
e
V
and
5.5
e
V
, respectively. The energy of the incident photon used for metal
R
, in
e
V
, is________.
Your Answer:
Validate
Solution:
From photoelectric equation,
E
=
φ
0
+
K.E.
max
For metals
P
and
Q
E
1
=
φ
P
+
K
E
P
⇒
E
1
−
4
=
E
P
and
E
1
−
4.5
=
E
O
E
P
=
2
E
O
(given)
∴
E
1
−
4
=
2
(
E
1
−
4.5
)
⇒
E
1
=
5
e
V
E
1
−
4
=
E
P
⇒
5
−
4
=
E
P
∴
E
P
=
1
e
V
and
E
Q
=
E
R
=
0.5
e
V
For metal
R
,
E
2
−
φ
R
=
K
E
R
∴
E
2
−
5.5
=
0.5
∴
E
2
=
0.5
+
5.5
=
6
e
V
© examsnet.com
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