Moving Charges & Magnetism PYQs Set 9 (PDF)

Set 9 of 19 · Questions 241-270 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 9 (Q241-270)
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241. $The fractional change in the magnetic field intensity at a distance 'r' from centre on the axis of current carrying coil of radius 'a' to the magnetic field intensity at the centre of the same coil is: (Take r < a)$ (1) $\frac{3}{2} \frac{a ^{2}}{r ^{2}}$ (2) $\frac{2}{3} \frac{a ^{2}}{r ^{2}}$ (3) $\frac{2}{3} \frac{r ^{2}}{a ^{2}}$ (4) $\frac{3}{2} \frac{r ^{2}}{a ^{2}}$ 242. $A proton beam enters a magnetic field of 10^{- 4} Wb m^{- 2} normally. If the specific charge of the proton is 10^{11} C kg^{- 1} and its velocity is 10^{9} m s^{- 1}, then the radius of the circle described will be$ (1) $10 m$ (2) $1 m$ (3) $0.1 m$ (4) $100 m$ 243. $A horizontal overhead powerline at a height of 5 m from the ground and carries a current of 150 A from East to West. The magnetic field directly below it on ground is$ (1) $6\times 1 0^{- 6} T, towards South$ (2) $6\times 1 0^{- 6} T, towards West$ (3) $7 \times 10^{- 6} T, towards East$ (4) $8 \times 10^{- 7} T, towards North$ 244. $A galvanometer of resistance 50Ω is connected to a battery of 3 V along with a resistance 2950Ω in series. A full deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be$ (1) $5050Ω$ (2) $6050Ω$ (3) $4450Ω$ (4) $5550Ω$ 245. $A toroid core has inner radius of 0.24 m and outer radius of 0.26 m . A current of 10 A flows through the wire having 2500 turns around it. Find the magnetic field inside the core of the toroid.$ (1) $π \times 10^{- 2} T$ (2) $2π\times 1 0^{- 2} T$ (3) $2 \times 10^{- 2} T$ (4) $20 \times 10^{- 2} T$ 246. $A positively charged particle moving due East enters a region of uniform magnetic field directed vertically upwards. This particle will$ (1) $move in a circular path with a decreased speed$ (2) $move in a circular path with a uniform speed$ (3) $get deflected in vertically upward direction$ (4) $move in circular path with an increased speed$ 247. $A charge moving with velocity v in X ‐direction is subjected to a field of magnetic induction in negative X ‐direction. As a result, the charge will$ (1) $remain unaffected$ (2) $start moving in a circular path Y‐Z plane$ (3) $retard along X ‐axis$ (4) $moving along a helical path around X ‐axis.$ 248. $To produce a magnetic field of π tesla at the centre of circular loop of diameter 1 m, the current flowing through loop is$ (1) $5 \times 10^{6} A$ (2) $10^{7} A$ (3) $2.5 \times 10^{6} A$ (4) $2 \times 10^{6} A$ 249. $In the cyclotron, as radius of the circular path of the charged particle increases (ω = angular velocity, v = linear velocity)$ (1) $both ω and v increases$ (2) $only ω increases, v remains constant$ (3) $v increases, ω remains constant$ (4) $v increases, ω decreases$ 250. $A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the center of solenoid is (Take, μ_{0} = 4 π \times 10^{- 7} Tm A^{- 1}) [NEET 2020]$ (1) $3.14 \times 10^{- 4} T$ (2) $6.28 \times 10^{- 5} T$ (3) $3.14 \times 10^{- 5} T$ (4) $6.28 \times 10^{- 4} T$ 251. $The distance moved by a charged particle along the magnetic field (the component of velocity is parallel to the magnetic field) in one rotation is given by (- mass of the particle, v - velocity of the particle, q charge of the particle, B - magnetic field)$ (1) $\frac{2 πmv}{qB}$ (2) $\frac{πmv}{qB}$ (3) $\frac{4 πmv}{qB}$ (4) $\frac{2 πmv}{qB ^{2}}$ 252. $A bar magnet having a magnetic moment of 2.0 \times 10^{5} JT^{- 1}, is placed along the direction of uniform magnetic field of magnitude B = 14 \times 10^{- 5} T . The work done in rotating the magnet slowly through 60^{\circ} from the direction of field is$ (1) $14 J$ (2) $8.4 J$ (3) $4 J$ (4) $1.4 J$ 253. $A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B . If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be$ (1) $1.5 MeV$ (2) $1 MeV$ (3) $4 MeV$ (4) $0.5 MeV$ 254. $Two long straight parallel conductors 10 cm apart, carry equal currents of magnitude 3 A in the same direction. Then, the magnetic induction at a point midway between them is$ (1) $2 \times 10^{- 5} T$ (2) $3 \times 10^{- 5} T$ (3) $zero$ (4) $4 \times 10^{- 5} T$ 255. $Which of the field pattern given below is valid for electric field as well as for magnetic field?$ (1) (2) (3) (4) 256. $The magnetic force q [v \times B] is$ (1) $parallel to both v and B$ (2) $perpendicular to V$ (3) $perpendicular to both V and B$ (4) $parallel to B$ 257. $A wire of length l carries a current I along the X -axis. The magnetic force acting on the wire is given by F = IB_{0} l (k - j) T, where B 0 is a constant. The existing magnetic field B is$ (1) $B_{0} i$ (2) $B_{0} (i + j - k)$ (3) $B_{0} (i + j + k)$ (4) $B_{0} (i - j - k)$ 258. $A proton and an alpha particle of the same speed enter in a uniform magnetic field which is acting perpendicular to their direction of motion. The ratio of the circular paths described by the alpha particle and proton is:$ (1) $1 : 4$ (2) $4 : 1$ (3) $2 : 1$ (4) $1 : 2$ 259. $A closely wound solenoid of 2000 turns and area of cross‐section 1.5 \times 1 0^{- 4} m^{2} carries a current of 2.0 A. It is suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field 5 \times 1 0^{- 2} tesla making an angle of 3 0^{o} with the axis of the solenoid. The torque on the solenoid will be$ (1) $3 \times 1 0^{- 3} Nm$ (2) $1.5 \times 1 0^{- 3} Nm$ (3) $1.5 \times 1 0^{- 2} Nm$ (4) $3\times 1 0^{- 2} Nm.$ 260. $An electron, a proton and an alpha particle having the same kinetic energy are moving in circular orbits of radii r_{e}, r_{p}, r_{α} respectively in uniform magnetic field B. The relation between r_{e}, r_{p}, r_{α} is:$ (1) $r_{e} < r_{p} < r_{α}$ (2) $r_{e} < r_{α} < r_{p}$ (3) $re > rp = rα$ (4) $re < rp = rα$ 261. $A proton and an alpha-particle moving with the same velocity enter a uniform magnetic field with their velocities perpendicular to the magnetic field. The ratio of radii of their circular paths is$ (1) $2 : 1$ (2) $1 : 4$ (3) $4 : 1$ (4) $1 : 2$ 262. $The deflection in a moving coil galvanometer is reduced to half when it is shunted with a 40Ω coil. The resistance of the galvanometer is$ (1) $80Ω$ (2) $40Ω$ (3) $20Ω$ (4) $15Ω$ 263. $A metal surface is illuminated by a radiation of wavelength 4500 A 0 . The ejected photo-electron enters a constant magnetic field of 2 mT making an angle of 90° with the magnetic field. If it starts revolving in a circular path of radius 2 mm, the work function of the metal is approximately:$ (1) $1.36 eV$ (2) $1.69 eV$ (3) $2.78 eV$ (4) $2.23 eV$ 264. $A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction 1 0^{- 4} Wb / m^{2} (= 1.0 gauss), the orbital radius of electron is$ (1) $11 cm$ (2) $18 cm$ (3) $12 cm$ (4) $16 cm$ 265. $A long solenoid of radius 1 mm has 100 turns per mm. If 1 A current flows in the solenoid, the magnetic field strength at the center of the solenoid is [NEET 2022]$ (1) $12.56 \times 10^{- 2} T$ (2) $12.56 \times 10^{- 4} T$ (3) $6.28 \times 10^{- 4} T$ (4) $6.28 \times 10^{- 2} T$ 266. $A charge particle moving in magnetic field B, has the components of velocity along B as well as perpendicular to B. The path of the charge particle will be$ (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) $straight along the direction of magnetic field B$ 267. $A. 250 turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180^{\circ} against the torque is [NEET 2017]$ (1) $9.1 μJ$ (2) $4.55 μJ$ (3) $2.3 μJ$ (4) $1.5 μJ$ 268. $A proton moving in perpendicular magnetic field possess energy ' E'. The strength of magnetic field is increased four times. But the proton is constrained to move in the path of same radius. The kinetic energy of proton will increase$ (1) $12 times$ (2) $8 times$ (3) $4 times$ (4) $16 times$ 269. $A circular loop and a square loop are formed from two wires of same length and cross section. Same current is passed through them. Then, the ratio of their dipole moments is.$ (1) $4$ (2) $\frac{2}{π}$ (3) $2$ (4) $\frac{4}{π}$ 270. $A short bar magnet placed with its axis at 30^{\circ} with an external field of 800 Gauss, experiences a torque of 0.016 N . m . The work done in moving it from most stable to most unstable position is α \times 10^{- 3} J . The value of α is____.$