1
JEE Main 2018 (Offline)
+4
-1
The dipole moment of a circular loop carrying a current I, is m and the magnetic field at the centre of the loop is B1. When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of the loop is $${{B_2}}$$. The ratio $${{{B_1}} \over {{B_2}}}$$ is:
A
2
B
$$\sqrt 3$$
C
$$\sqrt 2$$
D
$$1 \over \sqrt 2$$
2
JEE Main 2018 (Online) 15th April Evening Slot
+4
-1
A current of 1 A is flowing on the sides of an equilateral triangle of side 4.5 $$\times$$ 10-2 m. The magnetic field at the center of the triangle will be :
A
2 $$\times$$ 10-5 Wb/m2
B
Zero
C
8 $$\times$$ 10-5 Wb/m2
D
4 $$\times$$ 10-5 Wb/m2
3
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
$${{4N{\mu _0}{\rm I}} \over {{5^{3/2}}R}}$$
4
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
EXAM MAP
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