1
WB JEE 2021
MCQ (Single Correct Answer)
+1
-0.25
Change Language
A metal sphere of radius R carrying charge q is surrounded by a thick concentric metal shell of inner and outer radii a and b, respectively. The net charge on the shell is zero. The potential at the centre of the sphere, when the outer surface of the shell is grounded will be
A
$${q \over {4\pi {\varepsilon _0}}}\left( {{1 \over a} - {1 \over b}} \right)$$
B
$${q \over {4\pi {\varepsilon _0}}} - {1 \over a}$$
C
$${q \over {4\pi {\varepsilon _0}}}\left( {{1 \over R} - {1 \over a}} \right)$$
D
$${q \over {4\pi {\varepsilon _0}}} - {1 \over R}$$
2
WB JEE 2021
MCQ (Single Correct Answer)
+1
-0.25
Change Language
Three infinite plane sheets carrying uniform charge densities $$-$$ $$\sigma$$, 2$$\sigma$$, 4$$\sigma$$ are placed parallel to XZ-plane at Y = a, 3a, 4a respectively. The electric field at the point (0, 2a, 0) is
A
$${{5\sigma } \over {2{\varepsilon _0}}}\widehat j$$
B
$$ - {{7\sigma } \over {2{\varepsilon _0}}}\widehat j$$
C
$${\sigma \over {2{\varepsilon _0}}}\widehat j$$
D
$${{5\sigma } \over { - 2{\varepsilon _0}}}\widehat j$$
3
WB JEE 2021
MCQ (Single Correct Answer)
+1
-0.25
Change Language
Two point charges +q1 and +q2 are placed a finite distance d apart. It is desired to put a third charge q3 in between these two charges, so that q3 is in equilibrium. This is
A
possible only if q3 is negative.
B
possible only if q3 is positive.
C
possible irrespective of the sign of q3.
D
not possible at all.
4
WB JEE 2021
MCQ (Single Correct Answer)
+1
-0.25
Change Language
WB JEE 2021 Physics - Magnetism Question 12 English
Consider two infinitely long wires parallel to Z-axis carrying same current I in the positive z-direction. One wire passes through the point L at coordinates ($$-$$1, +1) and the other wire passes through the point M at coordinates ($$-$$1, $$-$$1). The resultant magnetic field at the origin O will be
A
$${{{\mu _0}I} \over {2\sqrt 2 \pi }}\widehat j$$
B
$${{{\mu _0}I} \over {2\pi }}\widehat j$$
C
$${{{\mu _0}I} \over {2\sqrt 2 \pi }}\widehat i$$
D
$${{{\mu _0}I} \over {4\pi }}\widehat i$$
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