Moving Charges & Magnetism PYQs Set 7 (PDF)

Set 7 of 19 · Questions 181-210 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 7 (Q181-210)
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181. $A toroid has an iron core with an Internal Magnetic field of 10 πmT, when the current in the winding of 1500 turns per metre is 10 A . Determine the field due to magnetisation (μ_{0} = 4 π \times 10^{- 7} Hm^{- 1})$ (1) $(4 π) mT$ (2) $(10 π) mT$ (3) $(\frac{8}{π}) mT$ (4) $(\frac{π}{4}) mT$ 182. $A bar magnet having a magnetic moment of 2.0 x 1 0^{5} J T^{- 1}, is placed along the direction of uniform magnetic field of magnitude B= 14 x 1 0^{- 5} T. The work done in rotating the magnet slowly through 60° from the direction of field is:$ (1) $14J$ (2) $8.4J$ (3) $4J$ (4) $1.4J$ 183. $A current i flows in an infinitely long, straight and thin walled pipe, then$ (1) $the magnetic field at all the points inside the pipe is same, but not zero$ (2) $the magnetic field at any point inside the pipe is zero$ (3) $the magnetic field is zero only on the axis of the pipe$ (4) $the magnetic field is different at different points inside the pipe$ 184. $Sensitivity of moving coil galvanometer is s. If a shunt of (\frac{1}{8})^{th} of the resistance of galvanometer is connected to moving coil galvanometer, its sensitivity becomes$ (1) $\frac{s}{3}$ (2) $\frac{s}{6}$ (3) $\frac{s}{9}$ (4) $\frac{5}{12}$ 185. $To convert a galvanometer into a ammeter, one needs to connect a$ (1) $low resistance in parallel$ (2) $high resistance in parallel$ (3) $low resistance in series$ (4) $high resistance in series$ 186. $The magnetic induction at a point P which is at the distance of 4 cm from a long current carrying wire is 1 0^{- 3} T. The field of induction at a distance 12 cm from the current will be$ (1) $3.33 \times 1 0^{- 4} T$ (2) $1.11 \times 1 0^{- 4} T$ (3) $33 \times 1 0^{- 3} T$ (4) $9 \times 1 0^{- 3} T$ 187. $A galvanometer of resistance 40Ω gives a deflection of 10 divisions per mA . There are 50 divisions on the scale. Maximum current that can pass through it when a shunt resistance of 2Ω is connected is$ (1) $105 mA$ (2) $155 mA$ (3) $210 mA$ (4) $75 mA$ 188. $A charged particle moves along circular path in a uniform magnetic field in a cyclotron. The kinetic energy of the charged particle increases to 4 times its initial value. What will be the ratio of new radius to the original radius of circular path of the charged particle:$ (1) $1 : 1$ (2) $1 : 2$ (3) $2 : 1$ (4) $1 : 4$ 189. $A closely wound solenoid of length 1 m has 5 layers of 500 turns each. If the magnitude of magnetic field inside the solenoid near its center is 4.4 mT, the current carried is$ (1) $1.4 A$ (2) $1.5 A$ (3) $1.6 A$ (4) $1.8 A$ 190. $The dipole moment of a circular loop carrying a current I, is m and the magnetic field at the centre of the loop is B_{1} . When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of loop is B_{2} . The ratio \frac{B _{1}}{B _{2}} is:$ (1) $2$ (2) $\frac{1}{2}$ (3) $2$ (4) $3$ 191. $The time taken for the magnetic energy to reach 25 % of its maximum value, when a solenoid of resistance R,inductance L is connected to a battery, is:$ (1) $\frac{L}{R} l n 5$ (2) $infinite$ (3) $\frac{L}{R} l n 2$ (4) $\frac{L}{R} l n 10$ 192. $A charged particle (charge q) is moving in a circle of radius R with uniform speed v . The associated magnetic moment μ is given by$ (1) $qv R^{2}$ (2) $qv R^{2} /2$ (3) $qvR$ (4) $qvR /2$ 193. $The torque acting on a magnetic dipole placed in uniform magnetic field is zero, when the angle between the dipole axis and the magnetic field is$ (1) $zero$ (2) $45^{\circ}$ (3) $60^{\circ}$ (4) $90^{\circ}$ 194. $Ionized hydrogen atoms and α-particle with momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r_{H} : r_{α} will be:$ (1) $1 ; 4$ (2) $2 : 1$ (3) $1 : 2$ (4) $4 : 1$ 195. $There are four light-weight-rod samples A, B, C, D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted: (i) A is feebly repelled (ii) B is feebly attracted (iii) C is strongly attracted (iv) D remains unaffected Which one of the following is true?$ (1) $B is of a paramagnetic material$ (2) $C is of a diamagnetic material$ (3) $D is of a ferromagnetic material$ (4) $A is of a non-magnetic material$ 196. $A circular coil of 10 turns and radius 10 cm is placed in a uniform magnetic field of 0.1 T normal to the plane of the coil. If the current in the coil is 5 A, then the magnitude of the torque on the coil is$ (1) $500 πN - m$ (2) $0.05 πN - m$ (3) $0.005 πN - m$ (4) $zero$ 197. $An electron having mass m and kinetic energy E enter in uniform magnetic field B perpendicularly, then its frequency will be$ (1) $\frac{eE}{qvB}$ (2) $\frac{2 πm}{eB}$ (3) $\frac{eB}{2 πm}$ (4) $\frac{2 m}{eBE}$ 198. $A toroid has a non ferromagnetic core of inner radius 24 cm and outer radius 25 cm, around which 4900 turns of a wire are wound. If the current in the wire is 12 A, the magnetic field inside the core of the toroid is$ (1) $56 mT$ (2) $54 mT$ (3) $42 mT$ (4) $48 mT$ 199. $A wire of length L metre carrying a current I ampere is bent in the form of a circle. Magnitude of its magnetic moment is$ (1) $\frac{L ^{2} I ^{2}}{4 π}$ (2) $\frac{L ^{2} I}{4 π}$ (3) $\frac{LI}{4 π}$ (4) $\frac{L I ^{2}}{4 π}$ 200. $A long conducting wire having a current I flowing through it, is bent into a circular coil of N turns. Then it is bent into a circular coil of n turns. The magnetic field is calculated at the center of coils in both the cases. The ratio of the magnetic field in first case to that of second case is:$ (1) $N : n$ (2) $n2 : N2$ (3) $N^{2} : n^{2}$ (4) $n : N$ 201. $A steel wire of length 1 and magnetic moment M is bent into a semicircular arc of radius R . The new magnetic moment is$ (1) $M$ (2) $\frac{2 RM}{πl}$ (3) $\frac{2 M}{π}$ (4) $\frac{2 πRM}{l}$ 202. $The ratio of magnetic field at the centre of a current carrying circular coil to its magnetic moment is x . If the current and the radius both are doubled. The new ratio will become$ (1) $x /4$ (2) $x /8$ (3) $2 x$ (4) $4 x$ 203. $A thin magnetic needle is placed in a magnetic field of 200 G with its axis at 30^{\circ} to the direction of the field. Find the magnetic moment of the needle if it experiences a torque of 0.012 Nm in this field.$ (1) $1.2 Am^{2}$ (2) $12.0 Am^{2}$ (3) $0.6 Am^{2}$ (4) $6.0 Am^{2}$ 204. $A charged particle when enters a uniform magnetic field moves in a helical path. If its angular velocity is 4 π \times 10^{6} rads^{- 1} and its velocity in the direction of magnetic field is 3 \times 10^{5} ms^{- 1} then the pitch of the helix is$ (1) $5 cm$ (2) $10 cm$ (3) $15 cm$ (4) $20 cm$ 205. $The magnetic field at the origin due to a current element \| dl \| placed at a point with vector position r is$ (1) $\frac{μ _{0} i}{4 π} \frac{dl \times r}{r ^{2}}$ (2) $\frac{μ _{0} i}{4 π} \frac{r \times dl}{r}$ (3) $\frac{μ _{0} i}{4 π} \frac{dl \times r}{r ^{3}}$ (4) $\frac{μ _{0} i}{4 π} \frac{r \times dl}{r ^{3}}$ 206. $A proton and helium nucleus are shot into a magnetic field at right angles to the field with same kinetic energy. Then the ratio of their radii is$ (1) $1 : 1$ (2) $1 : 2$ (3) $2 : 1$ (4) $1 : 4$ 207. $The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 \times 1 0^{3} A m^{-1} . The current required to be passed in a solenoid of length 20 cm and number of turns 100, so that the magnetic gets demagnetized when inside the solenoid, is:$ (1) $30 mA$ (2) $60 mA$ (3) $3 A$ (4) $6 A$ 208. $A galvanometer having a coil of resistance 60 Ω shows full scale deflection when a current of 1.0 amp passes through it. It can be converted into an ammeter to read currents upto 5.0 amp by$ (1) $putting in series a resistance of 15 Ω$ (2) $putting in series a resistance of 240 Ω$ (3) $putting in parallel a resistance of 15 Ω$ (4) $putting in parallel a resistance of 240 Ω .$ 209. $The ratio of magnetic field at the centre of a current carrying coil of radius r to the magnetic field at distance r from the centre of coil on its axis is x : 1. The value of x is_____.$ 210. $A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of 2 \times 10^{5} ms^{- 1} . When the electric field is switched off, the proton moves along a circular path of radius 2 cm. The magnitude of electric field is x \times 10^{4} N / C . The value of x is . Take the mass of the proton = 1.6 \times 10^{- 27} kg .$