NEET-XII-Physics
P1 year:2019
- #25A hollow metal sphere of radius R is uniformly
charged. The electric field due to the sphere
at a distance r from the centre
(1) Increases as r increases for `` r < R`` and for
``r > R``
(2) Zero as r increases for `` r < R``, decreases as
r increases for `` r > R``
(3) Zero as r increases for `` r < R``, increases as
r increases for ``r > R``
(4) Decreases as r increases for `` r < R`` and for
``r > R``digAnsr: 2Ans : ( 2 )
Sol.
C
R
++
+
+
+
+ +
+
r
Q
Charge Q will be distributed over the surface
of hollow metal sphere.
(i) For r < R (inside)
By Gauss law,
en
in
0
q
E · dS 0= =
&implies; E
in
= 0 =∵
en
( q 0)
(ii) For r > R (outside)
++
+
+
+
+ +
+
r
0 2
1
E
r
E = 0
in
E
R
r
O
en
0
0
q
E · dS =
Here, q
en
= Q =∵
en
( q Q)
∴ 2
0
0
Q
E 4 r =
∴
0 2
1
E
r