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KEAM 2018 Physics and Chemistry Paper
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© examsnet.com
Question : 25
Total: 120
Two soap bubbles of radii 3 mm and 4 mm confined in vacuum coalesce isothermally to form a new bubble. The radius of the bubble formed (in mm) is
3
3.5
4
5
7
Validate
Solution:
Surface area new bubble = surface area of first bubble
+
surface area of second bubble
⇒
A
=
A
1
+
A
1
∵
Surface area of a bubble,
A
=
8
π
R
2
∴
8
π
R
2
=
8
π
R
1
2
+
8
π
R
2
2
⇒
R
2
=
R
1
2
+
R
2
2
(give that
R
1
=
3
m
m
,
R
2
=
4
m
m
)
⇒
R
2
=
(
3
)
2
+
(
4
)
2
⇒
R
=
5
m
m
© examsnet.com
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