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Test Index
JEE Main Physics Class 11 Properties of Solids and Liquids Questions Part 2 Questions
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© examsnet.com
Question : 56
Total: 100
Three rods of identical cross-section and lengths are made of three different materials of thermal conductivity
K
1
,
K
2
and
K
3
, respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at
100
°
C
and the other at
0
°
C
(see figure). If the joints of the rod are at
70
°
C
and
20
°
C
in steady state and there is no loss of energy from the surface of the rod, the correct relationship between
K
1
,
K
2
and
K
3
is:
[Sep. 06, 2020 (II)]
K
1
:
K
3
=
2
:
3
,
K
1
<
K
3
=
2
:
5
K
1
<
K
2
<
K
3
K
1
:
K
2
=
5
:
2
,
K
1
:
K
3
=
3
:
5
K
1
>
K
2
>
K
3
Validate
Solution:
As the rods are identical, so they have same length (l) and area of cross-section (A). They are connected in series.
So, heat current will be same for all rods.
Heat current
=
(
Δ
Q
Δ
t
)
A
B
=
(
Δ
Q
Δ
t
)
B
C
=
(
Δ
Q
Δ
t
)
C
D
⇒
(
100
−
70
)
K
1
A
l
=
(
70
−
20
)
K
2
A
l
=
(
20
−
0
)
K
3
A
l
⇒
K
1
(
100
−
70
)
=
K
2
(
70
−
20
)
=
K
3
(
20
−
0
)
⇒
K
1
(
30
)
=
K
2
(
50
)
=
K
3
(
20
)
⇒
K
1
10
=
K
2
6
=
K
3
15
⇒
K
1
:
K
2
:
K
3
=
10
:
6
:
15
⇒
K
1
:
K
3
=
2
:
3
© examsnet.com
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