Moving Charges & Magnetism PYQs Set 10 (PDF)

Set 10 of 19 · Questions 271-300 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 10 (Q271-300)
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271. $A proton and an α -particle (with their masses in the ratio 1:4 and charges in the ratio of 1 : 2) are accelerated from rest through a potential difference V . If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii r_{p} : r_{α} of the circular paths described by them will be$ (1) $1 : 3$ (2) $1 : 2$ (3) $1 : 2$ (4) $1 : 3$ 272. $A magnetic field intensity at the centre of a circular wire of radius 0.1 m carrying a current 0.2 A is$ (1) $2 π \times 10^{- 5} T$ (2) $π\times 1 0^{- 7} T$ (3) $10^{- 7} T$ (4) $4π\times 1 0^{- 7} T$ 273. $A long solenoid carrying a current produces a magnetic field B along its axis. Ifthe current is doubled and the number of turns per cm is halved, the new value of the magnetic field is$ (1) $B /2$ (2) $B$ (3) $2 B$ (4) $4 B$ 274. $Charge q is uniformly spread on a thin ring of radius R . The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is$ (1) $\frac{μ _{0} qf}{2 πR}$ (2) $\frac{μ _{0} qf}{2 R}$ (3) $\frac{μ _{0} q}{2 fR}$ (4) $\frac{μ _{0} q}{2 πfR}$ 275. $A circular loop of area 0.01 m^{2} carrying a current of 10 A, is held perpendicular to a magnetic field of intensity 0. 1 T. The torque acting on the loop is$ (1) $0.001 Nm$ (2) $0.8 Nm$ (3) $zero$ (4) $0.01 Nm$ 276. $A bar magnet with a magnetic moment 5,0 A m^{2} is placed in parallel position relative to a magnetic field of 0.4 T. The amount of required work done in turning the magnet form parallel to antiparallel position relative to the field direction is________.$ (1) $4J$ (2) $1 J$ (3) $2 J$ (4) $Zero$ 277. $A particle of charge e and mass m moves with a velocity v in a magnetic field B applied perpendicular to the motion of the particle. The radius r of its path in the field is$ (1) $\frac{mv}{Be}$ (2) $\frac{Be}{mv}$ (3) $\frac{ev}{Bm}$ (4) $\frac{Bv}{em}$ 278. $The magnetic field normal to the plane of a coil of turns and radius which carries a current is measured on the axis of the coil at a distance from the centre of the coil. This is smaller than the field at the centre by the fraction,$ (1) $\frac{3}{2} \cdot \frac{h ^{2}}{r ^{2}}$ (2) $\frac{2}{3} \cdot \frac{h ^{2}}{r ^{2}}$ (3) $\frac{3}{2} \cdot \frac{r ^{2}}{h ^{2}}$ (4) $\frac{2}{3} \cdot \frac{r ^{2}}{h ^{2}}$ 279. $The magnetic field associated with a light wave is given at the origin by B = B_{0} (si n (3.14 \times 10^{7}) ct + si n (6.28 \times 10^{7}) ct) If this light falls on a silver plate having a work function of 4.7 eV, what will be the maximum kinetic energy of the photoelectrons? (c = 3 \times 10^{8} ms^{- 1}, h = 6.6 \times 10^{- 34} J - s)$ (1) $6.82 eV$ (2) $12.5 eV$ (3) $8.52 eV$ (4) $7.72 eV$ 280. $A proton moving with a constant velocity passes through a region of space without any change in its velocity. If E and B represent the electric and magnetic fields respectively, then the region of space may have:(A) E = 0, B = 0 (B) E = 0, B \neq = 0 (C) E \neq = 0, B = 0 (D) E \neq = 0, B \neq = 0 Choose the most appropriate answer from the options given below:$ (1) $(A), (B) and (C) only$ (2) $(A), (C) and (D) only$ (3) $(A), (B) and (D) only$ (4) $(B), (C) and (D) only$ 281. $A magnetic needle suspended parallel to a magnetic field requires 3 J of work to turn it through 6 0^{o} . The torque needed to maintain the needle in this position will be$ (1) $23 J$ (2) $3 J$ (3) $3 J$ (4) $\frac{3}{2} J$ 282. $If a long hollow copper pipe carries a current, then produced magnetic field will be$ (1) $both inside and outside the pipe$ (2) $outside the pipe only$ (3) $inside the pipe only$ (4) $neither inside nor outside the pipe$ 283. $Two charged particles, having same kinetic energy, are allowed to pass through a uniform magnetic field perpendicular to the direction of motion. If the ratio of radii of their circular paths is 6 : 5 and their respective masses ratio is 9 : 4. Then, the ratio of their charges will be:$ (1) $8 : 5$ (2) $5 : 4$ (3) $5 : 3$ (4) $8 : 7$ 284. $Energy in a current carrying coil is stored in the form of$ (1) $electric field only$ (2) $magnetic field only$ (3) $dielectric strength$ (4) $both(a) and(b)$ 285. $In cyclotron, for a given magnet, tadius of the semicircle traced by positive ion is directly proportional to (v = velocity of positive ion)$ (1) $v^{- 2}$ (2) $v^{- 1}$ (3) $v$ (4) $v^{2}$ 286. $A proton, a deuteron and an a-particle with same kinetic energy enter into a uniform magnetic field at right angle to magnetic field. The ratio of the radii of their respective circular paths is:$ (1) $1 : 2 : 2$ (2) $l: l : 2$ (3) $2 : 1 : 1$ (4) $1 : 2 : 1$ 287. $Ionized hydrogen atoms and α－particle with same momenta enters perpendicular to a constant magnetic field B. The ratio of their radii of their paths r_{H} : r_{α} will be [NEET 2019]$ (1) $1 : 2$ (2) $4 : 1$ (3) $1 : 4$ (4) $2 : 1$ 288. $An alternating electric field of frequency ' v' is applied across the dees (radius R) of a cyclotion to accelerate protons (mass m). The operating magnetic field ' B' used and K.E. of the proton beam produced by it are respectively (e = charge on proton)$ (1) $\frac{2 πmv}{e}, 2 π^{2} m v^{2} R^{2}$ (2) $\frac{2 π ^{2} mv}{e ^{2}}, 4 π^{2} m v^{2} R^{2}$ (3) $\frac{πmv}{e}, π^{2} m v^{2} R^{2}$ (4) $\frac{2 π ^{2} m ^{2} v ^{2}}{e}, 2 π^{2} m^{2} v^{2} R^{2}$ 289. $A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying acurrent I, the net force on the loop will be$ (1) $\frac{2 μ _{0} IiL}{3 π}$ (2) $\frac{μ _{0} IiL}{2 π}$ (3) $\frac{2 μ _{0} Ii}{3 π}$ (4) $\frac{μ _{0} Ii}{2 π}$ 290. $Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I_{1} and I_{2} currents, respectively Point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be$ (1) $\frac{μ _{0}}{2 πd} (\frac{I _{1}}{I _{2}})$ (2) $\frac{μ _{0}}{2 πd} (I_{1} + I_{2})$ (3) $\frac{μ _{0}}{2 πd} (I_{1}^{2} - I_{2}^{2})$ (4) $\frac{μ _{0}}{2 πd} (I_{1}^{2} + I_{2}^{2})^{1/2}$ 291. $A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current I_{1} at a distance d from the conductor as shown in figure. The loop will experience:$ (1) $a net repulsive force away from the conductor$ (2) $a net torque acting upward perpendicular to the horizontal plane$ (3) $a net torque acting downward normal to the horizontal plane$ (4) $a net attractive force towards the conductor$ 292. $The magnetic force acting on a charged particle of charge - 2 μC in a magnetic field of 2 T acting in y direction, when the particle velocity is (2 i + 3 j) \times 1 0^{6} m s^{- 1} is$ (1) $4 N in z direction$ (2) $8 N in y direction$ (3) $8 N in z direction$ (4) $8 N in - z direction$ 293. $A very long straight wire carries a current I . At the instant when a charge + Q at point P has velocity v, as shown, the force on the charge is$ (1) $along Oy$ (2) $opposite to Oy$ (3) $along Ox$ (4) $opposite to Ox.$ 294. $A thick current carrying cable of radius R carries current I uniformly distributed across its cross-section. The variation of magnetic field B due to the cable with the distance r from the axis of the cable is represented by [NEET 2021]$ (1) (2) (3) (4) 295. $Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2 I, respectively. The resultant magnetic field induction at the centre will be:$ (1) $\frac{5 μ _{0} I}{2 R}$ (2) $\frac{3 μ _{0} I}{2 R}$ (3) $\frac{μ _{0} I}{2 R}$ (4) $\frac{μ _{0} I}{R}$ 296. $An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current I along the same direction is shown in figure. Magnitude of force per unit length on the middle wire B is given by [NEET 2017]$ (1) $\frac{μ _{0} I ^{2}}{2 πd}$ (2) $\frac{2 μ _{0} I ^{2}}{πd}$ (3) $\frac{2 μ _{0} I ^{2}}{πd}$ (4) $\frac{μ _{0} I ^{2}}{2 πd}$ 297. $A proton with a kinetic energy of 2.0 eV moves into a region of uniform magnetic field of magnitude \frac{π}{2} x 10-3 T. The angle between the direction of magnetic field and velocity of proton is 60°. The pitch of the helical path taken by the proton is____cm. (Take, mass of proton = 1. 6 x 10-27 kg and charge on proton = 1.6 x 10-19C).$ 298. $The magnetic potential due to a magnetic dipole at a point on its axis situated at a distance of 20 cm from its center is 1.5 \times 10^{- 5} Tm . The magnetic moment of the dipole is ______Am^{2} . (Given : \frac{μ _{0}}{4 π} = 10^{- 7} TmA^{- 1})$ 299. $A charge of 4.0 μC is moving with a velocity of 4.0 \times 10^{6} ms^{- 1} along the positive y -axis under a magnetic field B of strength (2 k) T. The force acting on the charge is x i N . The value of x is_______$ 300. $Two parallel long current carrying wire separated by a distance 2 r are shown in the figure. The ratio of magnetic field at A to the magnetic field produced at C is \frac{x}{7} . The value of x is_______$