1
JEE Main 2023 (Online) 31st January Evening Shift
+4
-1
A long conducting wire having a current I flowing through it, is bent into a circular coil of $\mathrm{N}$ turns. Then it is bent into a circular coil of $\mathrm{n}$ turns. The magnetic field is calculated at the centre of coils in both the cases. The ratio of the magnetic field in first case to that of second case is :
A
$N^{2}: n^{2}$
B
$\mathrm{N}: \mathrm{n}$
C
$\mathrm{n}: \mathrm{N}$
D
$n^{2}: N^{2}$
2
JEE Main 2023 (Online) 31st January Morning Shift
+4
-1

A rod with circular cross-section area $$2 \mathrm{~cm}^{2}$$ and length $$40 \mathrm{~cm}$$ is wound uniformly with 400 turns of an insulated wire. If a current of $$0.4 \mathrm{~A}$$ flows in the wire windings, the total magnetic flux produced inside windings is $$4 \pi \times 10^{-6} \mathrm{~Wb}$$. The relative permeability of the rod is

(Given : Permeability of vacuum $$\mu_{0}=4 \pi \times 10^{-7} \mathrm{NA}^{-2}$$)

A
$$\frac{5}{16}$$
B
125
C
$$\frac{32}{5}$$
D
12.5
3
JEE Main 2023 (Online) 30th January Evening Shift
+4
-1

As shown in the figure, a current of $2 \mathrm{~A}$ flowing in an equilateral triangle of side $4 \sqrt{3} \mathrm{~cm}$. The magnetic field at the centroid $\mathrm{O}$ of the triangle is

(Neglect the effect of earth's magnetic field)

A
$4 \sqrt{3} \times 10^{-4} \mathrm{~T}$
B
$4 \sqrt{3} \times 10^{-5} \mathrm{~T}$
C
$3 \sqrt{3} \times 10^{-5} \mathrm{~T}$
D
$\sqrt{3} \times 10^{-4} \mathrm{~T}$
4
JEE Main 2023 (Online) 30th January Evening Shift
+4
-1

A current carrying rectangular loop PQRS is made of uniform wire. The length $P R=Q S=5 \mathrm{~cm}$ and $P Q=R S=100 \mathrm{~cm}$. If ammeter current reading changes from I to $2 I$, the ratio of magnetic forces per unit length on the wire $P Q$ due to wire $R S$ in the two cases respectively $\left(f_{P Q}^I: f_{P Q}^{2 t}\right)$ is:

A
1 : 4
B
1 : 3
C
1 : 2
D
1 : 5
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