1
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
2
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
$${{4N{\mu _0}{\rm I}} \over {{5^{3/2}}R}}$$
3
JEE Main 2018 (Online) 15th April Morning Slot
+4
-1
The $$B$$-$$H$$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solended with $$1000$$ turns/cm. The current that should be passed in the solended to demagnetise the ferromagnet completely is :

A
$$1$$ $$mA$$
B
$$2$$ $$mA$$
C
$$20\,\mu A$$
D
$$40\,\mu A$$
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
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