Moving Charges & Magnetism PYQs Set 9 (PDF)

Set 9 of 17 · Questions 241-270 of 499

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Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 9 (Q241-270)
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241. $The deflection in a moving coil galvanometer is reduced to half when it is shunted with a 40Ω coil. The resistance of the galvanometer is$ (1) $80Ω$ (2) $40Ω$ (3) $20Ω$ (4) $15Ω$ 242. $A metal surface is illuminated by a radiation of wavelength 4500 A 0 . The ejected photo-electron enters a constant magnetic field of 2 mT making an angle of 90° with the magnetic field. If it starts revolving in a circular path of radius 2 mm, the work function of the metal is approximately:$ (1) $1.36 eV$ (2) $1.69 eV$ (3) $2.78 eV$ (4) $2.23 eV$ 243. $A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction 1 0^{- 4} Wb / m^{2} (= 1.0 gauss), the orbital radius of electron is$ (1) $11 cm$ (2) $18 cm$ (3) $12 cm$ (4) $16 cm$ 244. $A long solenoid of radius 1 mm has 100 turns per mm. If 1 A current flows in the solenoid, the magnetic field strength at the center of the solenoid is [NEET 2022]$ (1) $12.56 \times 10^{- 2} T$ (2) $12.56 \times 10^{- 4} T$ (3) $6.28 \times 10^{- 4} T$ (4) $6.28 \times 10^{- 2} T$ 245. $A charge particle moving in magnetic field B, has the components of velocity along B as well as perpendicular to B. The path of the charge particle will be$ (1) $helical path with the axis perpendicular to the direction of magnetic field B$ (2) $helical path with the axis along magnetic field B$ (3) $circular path$ (4) $straight along the direction of magnetic field B$ 246. $A. 250 turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180^{\circ} against the torque is [NEET 2017]$ (1) $9.1 μJ$ (2) $4.55 μJ$ (3) $2.3 μJ$ (4) $1.5 μJ$ 247. $A proton moving in perpendicular magnetic field possess energy ' E'. The strength of magnetic field is increased four times. But the proton is constrained to move in the path of same radius. The kinetic energy of proton will increase$ (1) $12 times$ (2) $8 times$ (3) $4 times$ (4) $16 times$ 248. $A circular loop and a square loop are formed from two wires of same length and cross section. Same current is passed through them. Then, the ratio of their dipole moments is.$ (1) $4$ (2) $\frac{2}{π}$ (3) $2$ (4) $\frac{4}{π}$ 249. $A proton and an α -particle (with their masses in the ratio 1:4 and charges in the ratio of 1 : 2) are accelerated from rest through a potential difference V . If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii r_{p} : r_{α} of the circular paths described by them will be$ (1) $1 : 3$ (2) $1 : 2$ (3) $1 : 2$ (4) $1 : 3$ 250. $A magnetic field intensity at the centre of a circular wire of radius 0.1 m carrying a current 0.2 A is$ (1) $2 π \times 10^{- 5} T$ (2) $π\times 1 0^{- 7} T$ (3) $10^{- 7} T$ (4) $4π\times 1 0^{- 7} T$ 251. $A long solenoid carrying a current produces a magnetic field B along its axis. Ifthe current is doubled and the number of turns per cm is halved, the new value of the magnetic field is$ (1) $B /2$ (2) $B$ (3) $2 B$ (4) $4 B$ 252. $Charge q is uniformly spread on a thin ring of radius R . The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is$ (1) $\frac{μ _{0} qf}{2 πR}$ (2) $\frac{μ _{0} qf}{2 R}$ (3) $\frac{μ _{0} q}{2 fR}$ (4) $\frac{μ _{0} q}{2 πfR}$ 253. $A circular loop of area 0.01 m^{2} carrying a current of 10 A, is held perpendicular to a magnetic field of intensity 0. 1 T. The torque acting on the loop is$ (1) $0.001 Nm$ (2) $0.8 Nm$ (3) $zero$ (4) $0.01 Nm$ 254. $A bar magnet with a magnetic moment 5,0 A m^{2} is placed in parallel position relative to a magnetic field of 0.4 T. The amount of required work done in turning the magnet form parallel to antiparallel position relative to the field direction is________.$ (1) $4J$ (2) $1 J$ (3) $2 J$ (4) $Zero$ 255. $A particle of charge e and mass m moves with a velocity v in a magnetic field B applied perpendicular to the motion of the particle. The radius r of its path in the field is$ (1) $\frac{mv}{Be}$ (2) $\frac{Be}{mv}$ (3) $\frac{ev}{Bm}$ (4) $\frac{Bv}{em}$ 256. $The magnetic field normal to the plane of a coil of turns and radius which carries a current is measured on the axis of the coil at a distance from the centre of the coil. This is smaller than the field at the centre by the fraction,$ (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) $\frac{2}{3} \cdot \frac{r ^{2}}{h ^{2}}$ 257. $The magnetic field associated with a light wave is given at the origin by B = B_{0} (si n (3.14 \times 10^{7}) ct + si n (6.28 \times 10^{7}) ct) If this light falls on a silver plate having a work function of 4.7 eV, what will be the maximum kinetic energy of the photoelectrons? (c = 3 \times 10^{8} ms^{- 1}, h = 6.6 \times 10^{- 34} J - s)$ (1) $6.82 eV$ (2) $12.5 eV$ (3) $8.52 eV$ (4) $7.72 eV$ 258. $A proton moving with a constant velocity passes through a region of space without any change in its velocity. If E and B represent the electric and magnetic fields respectively, then the region of space may have:(A) E = 0, B = 0 (B) E = 0, B \neq = 0 (C) E \neq = 0, B = 0 (D) E \neq = 0, B \neq = 0 Choose the most appropriate answer from the options given below:$ (1) $(A), (B) and (C) only$ (2) $(A), (C) and (D) only$ (3) $(A), (B) and (D) only$ (4) $(B), (C) and (D) only$ 259. $A magnetic needle suspended parallel to a magnetic field requires 3 J of work to turn it through 6 0^{o} . The torque needed to maintain the needle in this position will be$ (1) $23 J$ (2) $3 J$ (3) $3 J$ (4) $\frac{3}{2} J$ 260. $If a long hollow copper pipe carries a current, then produced magnetic field will be$ (1) $both inside and outside the pipe$ (2) $outside the pipe only$ (3) $inside the pipe only$ (4) $neither inside nor outside the pipe$ 261. $Two charged particles, having same kinetic energy, are allowed to pass through a uniform magnetic field perpendicular to the direction of motion. If the ratio of radii of their circular paths is 6 : 5 and their respective masses ratio is 9 : 4. Then, the ratio of their charges will be:$ (1) $8 : 5$ (2) $5 : 4$ (3) $5 : 3$ (4) $8 : 7$ 262. $Energy in a current carrying coil is stored in the form of$ (1) $electric field only$ (2) $magnetic field only$ (3) $dielectric strength$ (4) $both(a) and(b)$ 263. $In cyclotron, for a given magnet, tadius of the semicircle traced by positive ion is directly proportional to (v = velocity of positive ion)$ (1) $v^{- 2}$ (2) $v^{- 1}$ (3) $v$ (4) $v^{2}$ 264. $A proton, a deuteron and an a-particle with same kinetic energy enter into a uniform magnetic field at right angle to magnetic field. The ratio of the radii of their respective circular paths is:$ (1) $1 : 2 : 2$ (2) $l: l : 2$ (3) $2 : 1 : 1$ (4) $1 : 2 : 1$ 265. $Ionized hydrogen atoms and α－particle with same momenta enters perpendicular to a constant magnetic field B. The ratio of their radii of their paths r_{H} : r_{α} will be [NEET 2019]$ (1) $1 : 2$ (2) $4 : 1$ (3) $1 : 4$ (4) $2 : 1$ 266. $An alternating electric field of frequency ' v' is applied across the dees (radius R) of a cyclotion to accelerate protons (mass m). The operating magnetic field ' B' used and K.E. of the proton beam produced by it are respectively (e = charge on proton)$ (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) $\frac{2 π ^{2} m ^{2} v ^{2}}{e}, 2 π^{2} m^{2} v^{2} R^{2}$ 267. $A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying acurrent I, the net force on the loop will be$ (1) $\frac{2 μ _{0} IiL}{3 π}$ (2) $\frac{μ _{0} IiL}{2 π}$ (3) $\frac{2 μ _{0} Ii}{3 π}$ (4) $\frac{μ _{0} Ii}{2 π}$ 268. $Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I_{1} and I_{2} currents, respectively Point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be$ (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) $\frac{μ _{0}}{2 πd} (I_{1}^{2} + I_{2}^{2})^{1/2}$ 269. $A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current I_{1} at a distance d from the conductor as shown in figure. The loop will experience:$ (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) $a net attractive force towards the conductor$ 270. $The magnetic force acting on a charged particle of charge - 2 μC in a magnetic field of 2 T acting in y direction, when the particle velocity is (2 i + 3 j) \times 1 0^{6} m s^{- 1} is$ (1) $4 N in z direction$ (2) $8 N in y direction$ (3) $8 N in z direction$ (4) $8 N in - z direction$