1
JEE Main 2018 (Online) 15th April Morning Slot
+4
-1
A Helmholtz coil has a pair of loops, each with $$N$$ turns and radius $$R$$. They are placed coaxially at distance $$R$$ and the same current $${\rm I}$$ flows through the loops in the same direction. $$P,$$ midway between the centers $$A$$ and $$C$$, is given by [Refer to figure given below] :

A
$${{8N{\mu _0}{\rm I}} \over {{5^{1/2}}R}}$$
B
$${{8N{\mu _0}{\rm I}} \over {{5^{3/2}}R}}$$
C
$${{4N{\mu _0}{\rm I}} \over {{5^{1/2}}R}}$$
D
$${{4N{\mu _0}{\rm I}} \over {{5^{3/2}}R}}$$
2
JEE Main 2017 (Online) 9th April Morning Slot
+4
-1
A negative test charge is moving near a long straight wire carrying a current. The force acting on the test charge is parallel to the direction of the current. The motion of the charge is :
A
away from the wire
B
towards the wire
C
parallel to the wire along the current
D
parallel to the wire opposite to the current
3
JEE Main 2017 (Online) 8th April Morning Slot
+4
-1
A magnetic dipole in a constant magnetic field has :
A
maximum potential energy when the torque is maximum.
B
zero potential energy when the torque is minimum.
C
zero potential energy when the torque is maximum.
D
minimum potential energy when the torque is maximum.
4
JEE Main 2017 (Online) 8th April Morning Slot
+4
-1
In a certain region static electric and magnetic fields exist. The magnetic field is given by $$\overrightarrow B = {B_0}\left( {\widehat i + 2\widehat j - 4\widehat k} \right)$$ . If a test charge moving with a velocity $$\overrightarrow \upsilon = {\upsilon _0}\left( {3\widehat i - \widehat j + 2\widehat k} \right)$$ experiences no force in that region, then the electric field in the region, in SI units, is :
A
$$\overrightarrow E = - {\upsilon _0}\,{B_0}\left( {3\widehat i - 2\widehat j - 4\widehat k} \right)$$
B
$$\overrightarrow E = - {\upsilon _0}\,{B_0}\left( {\widehat i + \widehat j + 7\widehat k} \right)$$
C
$$\overrightarrow E = {\upsilon _0}\,{B_0}\left( {14\widehat j + 7\widehat k} \right)$$
D
$$\overrightarrow E = - {\upsilon _0}\,{B_0}\left( {14\widehat j + 7\widehat k} \right)$$
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