Magnetic Effects of Current & Magnetism · JEE Main previous year questions

1. A.A-III, B-IV, C-I, D-II
2. B.A-II, B-I, C-IV, D-III
3. C.A-III, B-I, C-IV, D-II
4. D.A-I, B-III, C-IV, D-II

A solenoid of 1200 turns is wound uniformly in a single layer on a glass tube 2 m long and 0.2 m in diameter. The magnetic intensity at the center of the solenoid when a current of 2 A flows through it is :

1. A.$1\mathrm{A}{\mathrm{m}}^{-1}$
2. B.$2.4\times 10^{-3}\mathrm{A}{\mathrm{m}}^{-1}$
3. C.$1.2\times 10^3\mathrm{A}{\mathrm{m}}^{-1}$
4. D.$2.4\times 10^3\mathrm{A}{\mathrm{m}}^{-1}$

A wire of length 1m moving with velocity 8 m/s at right angles to a magnetic field of 2T. The magnitude of induced emf, between the ends of wire will be __________.

1. A.20 V
2. B.8 V
3. C.16 V
4. D.12 V

For a moving coil galvanometer, the deflection in the coil is 0.05 rad when a current of 10 mA is passes through it. If the torsional constant of suspension wire is $4.0\times 10^{-5}\mathrm{N}\mathrm{m}\mathrm{ra}{\mathrm{d}}^{-1}$, the magnetic field is 0.01T and the number of turns in the coil is 200, the area of each turn (in $\mathrm{c}{\mathrm{m}}^2$) is :

1. A.1.5
2. B.2.0
3. C.0.5
4. D.1.0

Two long parallel wires carrying currents 8A and 15A in opposite directions are placed at a distance of 7 cm from each other. A point P is equidistant from both the wires such that the lines joining the point P to the wires are perpendicular to each other. The magnitude of magnetic field at P is ____ $\times 10^{-6}$ T. (Given : $\sqrt{2}=1.4$)

A circular loop of radius $r$ is carrying current I A. The ratio of magnetic field at the center of circular loop and at a distance r from the center of the loop on its axis is :

1. A.$3\sqrt{2}:2$
2. B.$1:3\sqrt{2}$
3. C.$2\sqrt{2}:1$
4. D.$1:\sqrt{2}$

A conducting circular loop of radius $\frac{10}{\sqrt{\pi }}\mathrm{cm}$ is placed perpendicular to a uniform magnetic field of $0.5\mathrm{T}$. The magnetic field is decreased to zero in $0.5\mathrm{s}$ at a steady rate. The induced emf in the circular loop at $0.25\mathrm{s}$ is :

1. A.$\mathrm{emf}=10\mathrm{mV}$
2. B.$\mathrm{emf}=5\mathrm{mV}$
3. C.$\mathrm{emf}=100\mathrm{mV}$
4. D.$\mathrm{emf}=1\mathrm{mV}$

A long solenoid is formed by winding $70\mathrm{turns}\mathrm{c}{\mathrm{m}}^{-1}$. If 2.0 A current flows, then the magnetic field produced inside the solenoid is ________ $({\mu }_0=4\pi \times 10^{-7}\mathrm{T}\mathrm{m}{\mathrm{A}}^{-1})$

1. A.$88\times 10^{-4}\mathrm{T}$
2. B.$1232\times 10^{-4}\mathrm{T}$
3. C.$176\times 10^{-4}\mathrm{T}$
4. D.$352\times 10^{-4}\mathrm{T}$

A single turn current loop in the shape of a right angle triangle with sides 5 cm, 12 cm, 13 cm is carrying a current of 2 A. The loop is in a uniform magnetic field of magnitude 0.75 T whose direction is parallel to the current in the 13 cm side of the loop. The magnitude of the magnetic force on the 5 cm side will be $\frac{x}{130}\mathrm{N}$. The value of $x$ is ___________.

A closely wound circular coil of radius $5\mathrm{cm}$ produces a magnetic field of $37.68\times 10^{-4}\mathrm{T}$ at its center. The current through the coil is ____ $\mathrm{A}$. [Given, number of turns in the coil is 100 and $\pi =3.14$]

A wire of length $314\mathrm{cm}$ carrying current of $14\mathrm{A}$ is bent to form a circle. The magnetic moment of the coil is ____ $\mathrm{A}-{\mathrm{m}}^2$. [Given $\pi =3.14$]

The vertical component of the earth's magnetic field is $6\times 10^{-5}\mathrm{T}$ at any place where the angle of dip is $37^{\circ }$. The earth's resultant magnetic field at that place will be (Given $\tan 37^{\circ }=\frac{3}{4}$)

1. A.$8\times 10^{-5}\mathrm{T}$
2. B.$6\times 10^{-5}\mathrm{T}$
3. C.$5\times 10^{-4}\mathrm{T}$
4. D.$1\times 10^{-4}\mathrm{T}$

The current sensitivity of a galvanometer can be increased by : (A) decreasing the number of turns (B) increasing the magnetic field (C) decreasing the area of the coil (D) decreasing the torsional constant of the spring Choose the most appropriate answer from the options given below :

1. A.(B) and (C) only
2. B.(C) and (D) only
3. C.(A) and (C) only
4. D.(B) and (D) only

1. A.$30\text{ A}$
2. B.$15\text{ A}$
3. C.$10\text{ A}$
4. D.$3\text{ A}$

1. A.$0.126\text{ N}$
2. B.$0.312\text{ N}$
3. C.$0.216\text{ N}$
4. D.$0.245\text{ N}$

The magnetic field at the center of current carrying circular loop is $B_1$. The magnetic field at a distance of $\sqrt{3}$ times radius of the given circular loop from the center on its axis is $B_2$. The value of $B_1/B_2$ will be

1. A.$9:4$
2. B.$12:\sqrt{5}$
3. C.$8:1$
4. D.$5:\sqrt{3}$

Two bar magnets oscillate in a horizontal plane in earth's magnetic field with time periods of $3\text{ s}$ and $4\text{ s}$ respectively. If their moments of inertia are in the ratio of $3:2$, then the ratio of their magnetic moments will be:

1. A.$2:1$
2. B.$8:3$
3. C.$1:3$
4. D.$27:16$

A cyclotron is used to accelerate protons. If the operating magnetic field is $1.0\mathrm{T}$ and the radius of the cyclotron 'dees' is $60\mathrm{cm}$, the kinetic energy of the accelerated protons in $\mathrm{MeV}$ will be : $[\text{use }{\mathrm{m}}_{\mathrm{p}}=1.6\times 10^{-27}\mathrm{kg},\mathrm{e}=1.6\times 10^{-19}\mathrm{C}]$

1. A.$12$
2. B.$18$
3. C.$16$
4. D.$32$

A compass needle of oscillation magnetometer oscillates 20 times per minute at a place $\mathrm{P}$ of dip $30^{\circ }$. The number of oscillations per minute become 10 at another place $\mathrm{Q}$ of $60^{\circ }$ dip. The ratio of the total magnetic field at the two places $(B_Q:B_P)$ is :

1. A.$\sqrt{3}:4$
2. B.$4:\sqrt{3}$
3. C.$\sqrt{3}:2$
4. D.$2:\sqrt{3}$

A conducting circular loop is placed in $X-Y$ plane in presence of magnetic field $\vec{\mathrm{B}}=\left(3t^3\hat{j}+3t^2\hat{k}\right)$ in SI unit. If the radius of the loop is $1\mathrm{m}$, the induced emf in the loop, at time, $t=2\mathrm{s}$ is $n\pi \mathrm{V}$. The value of $n$ is ____.

A charge particle is moving in a uniform magnetic field $(2\hat{i}+3\hat{j})\mathrm{T}$. If it has an acceleration of $(\alpha \hat{i}-4\hat{j})m/{\mathrm{s}}^2$, then the value of $\alpha$ will be :

1. A.3
2. B.6
3. C.12
4. D.2

${\mathrm{B}}_X$ and ${\mathrm{B}}_Y$ are the magnetic fields at the centre of two coils X and Y respectively each carrying equal current. If coil $X$ has 200 turns and $20\mathrm{cm}$ radius and coil $Y$ has 400 turns and $20\mathrm{cm}$ radius, the ratio of $B_X$ and $B_Y$ is :

1. A.$1:1$
2. B.$1:2$
3. C.$2:1$
4. D.$4:1$

Light wave travelling in air along x-direction is given by $E_y=540\sin \pi \times 10^4(x-ct){\text{ Vm}}^{-1}$. Then, the peak value of magnetic field of wave will be (Given $c=3\times 10^8{\text{ ms}}^{-1}$)

1. A.$18\times 10^{-7}\text{ T}$
2. B.$54\times 10^{-7}\text{ T}$
3. C.$54\times 10^{-8}\text{ T}$
4. D.$18\times 10^{-8}\text{ T}$

An electron with energy $0.1\text{ keV}$ moves at right angle to the earth's magnetic field of $1\times 10^{-4}{\text{ Wbm}}^{-2}$. The frequency of revolution of the electron will be : (Take mass of electron $=9.0\times 10^{-31}\text{ kg}$)

1. A.$1.6\times 10^5\text{ Hz}$
2. B.$5.6\times 10^5\text{ Hz}$
3. C.$2.8\times 10^6\text{ Hz}$
4. D.$1.8\times 10^6\text{ Hz}$

A coil of n number of turns wound tightly in the form of a spiral with inner and outer radii $r_1$ and $r_2$ respectively. When a current of strength I is passed through the coil, the magnetic field at its centre will be :

1. A.$\frac{{\mu }_{0}nI}{2(r_2-r_1)}$
2. B.$\frac{{\mu }_{0}nI}{r_2}$
3. C.$\frac{{\mu }_{0}nI}{r_2-r_1}{\log }_{\mathrm{e}}\frac{r_1}{r_2}$
4. D.$\frac{{\mu }_{0}nI}{2(r_2-r_1)}{\log }_{\mathrm{e}}\frac{r_2}{r_1}$