Moving Charges & Magnetism PYQs Set 14 (PDF)

Set 14 of 17 · Questions 391-420 of 499

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Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 14 (Q391-420)
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391. $Current ' I' is flowing in a conductor shaped as shown in the figure. The radius of the curved part is r and the length of straight portion is very large. The value of the magnetic field at the centre O will be$ (1) $\frac{μ _{0} I}{4 πr} (\frac{π}{2} + 1)$ (2) $\frac{μ _{0} I}{4 πr} (\frac{π}{2} - 1)$ (3) $\frac{μ _{0} I}{4 πr} (\frac{3 π}{2} + 1)$ (4) $\frac{μ _{0} I}{4 πr} (\frac{3 π}{2} - 1)$ 392. $A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B' at radial distances a/2 and 2a respectively, from the axis of the wire is [NEET 2016]$ (1) $\frac{1}{2}$ (2) $1$ (3) $4$ (4) $\frac{1}{4}$ 393. $A bar magnet of length ‘I’ and magnetic dipole moment ‘M’ is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be:$ (1) $\frac{3}{π} M$ (2) $\frac{2}{π} M$ (3) $\frac{M}{2}$ (4) $M$ 394. $Two long wires carrying current is 8 A and 6 A along x axes and y axes respectively. The magnetic field at the point (2 i + 4 j) is (Take μ_{0} = 4 π \times 10^{- 7} SI unit)$ (1) $1 \times 10^{- 6} T$ (2) $2 \times 10^{- 6} T$ (3) $1 \times 10^{- 7} T$ (4) $2 \times 10^{- 7} T$ 395. $A current carrying loop ABCD has two circular arcs AD and BC with radius 1 cm and 2 cm respectively as shown in the figure. The two arcs AD and BC subtend a common angle 30^{\circ} at the centre O . If the current flowing in the loop is \frac{1.2}{π} A, then the magnitude of net magnetic field at O is (Given μ_{0} = 4 π \times 10^{- 7})$ (1) $0.5 μT$ (2) $3 μT$ (3) $1 μT$ (4) $1.5 μT$ 396. $A galvanometer has a coil of resistance 100 ohm and gives a full scale deflection for 30 mA current. If it is work as a voltmeter of 30 volt range, the resistance required to be added will be$ (1) $900 Ω$ (2) $1800 Ω$ (3) $500 Ω$ (4) $1000 Ω .$ 397. $Two circular coils made from same wire but radius of 1^{st} coil is twice that of 2^{nd} coil. If magnetic field at their centres is same then ratio of potential difference applied across them is (1^{st}) to 2^{nd} coil)$ (1) $2$ (2) $3$ (3) $4$ (4) $6$ 398. $A charged particle of mass m and charge q moving under the influence of uniform electric field Ei \to and a uniform magnetic field B k \to follows a trajectory from point P to Q as shown in figure. The velocities at P and Q are respectively, v i \to and - 2 v j \to . Then which of the following statements (A, B, C, D) are the correct? (Trajectory shown is schematic and not to scale)$ (1) $Magnitude of electric field E_{0} = \frac{3}{4} (\frac{m v ^{2}}{qa})$ (2) $Rate of work done at point A is \frac{3}{4} \frac{m v ^{3}}{a}$ (3) $Rate of work done by both fields at point B is zero$ (4) $Change in angular momentum w.r.t. origin is 2 maV$ 399. $A straight conductor carrying current i splits into two parts as shown in the figure. The radius of the circular loop is R . The total magnetic field at the centre P at the loop is$ (1) $Zero$ (2) $3 μ_{0} i /32 R, outward$ (3) $3 μ_{0} i /32 R, inward$ (4) $\frac{μ _{0} i}{2 R}, inward I$ 400. $A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane. If the current in the loop is i. The resultant magnetic field due to the two semicircular parts at their common center is$ (1) $\frac{μ _{0} i}{2 2 R}$ (2) $\frac{μ _{0} i}{2 R}$ (3) $\frac{μ _{0} i}{4 R}$ (4) $\frac{μ _{0} i}{2 R}$ 401. $A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F_{1}, F_{2} and F_{3} respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is$ (1) $(F_{3} - F_{1})^{2} - F_{2}^{2}$ (2) $F_{3} - F_{1} + F_{2}$ (3) $F_{3} - F_{1} - F_{2}$ (4) $(F_{3} - F_{1})^{2} + F_{2}^{2} .$ 402. $Hysteresis loops for two magnetic materials A and B are given below: These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use:$ (1) $A for electromagnets and B for electric generators.$ (2) $A for transformers and B for electric generators.$ (3) $B for electromagnets and transformers.$ (4) $A for electric generators and transformers.$ 403. $A current I is flowing through the loop. The direction of the current and the shape of the loop are as shown in the figure. The magnetic field at the center of the loop is \frac{μ _{0} I}{R} times ((MA = R, MB = 2 R, ∠ DMA = 90^{\circ})$ (1) $5/16, but out of the plane of the paper.$ (2) $5/16, but into the plane of the paper.$ (3) $7/16, but out of the plane of the paper.$ (4) $7/16, but into the plane of the paper.$ 404. $Proton with kinetic energy of 1 MeV moves from south to north. It gets an acceleration of 10^{12} m / s^{2} by an applied magnetic field (west to east). The value of magnetic field: (Rest mass of proton is 1.6 \times 10^{- 27} Kg)$ (1) $0.71 mT$ (2) $7.1 mT$ (3) $71 mT$ (4) $710 mT$ 405. $PQ and RS are long parallel conductors separated by certain distance. M is the midpoint between them (see the figure). The net magnetic field at M is B . Now, the current 2 A is switched off. The field at M now becomes$ (1) $2 B$ (2) $B$ (3) $B /2$ (4) $3 B$ 406. $An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of 10^{5} m / s parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the magnitude of the force experienced by the electron at that instant [NEET 2021]$ (1) $8 \times 10^{- 20} N$ (2) $4 \times 10^{- 20} N$ (3) $8 π \times 10^{- 20} N$ (4) $4 π \times 10^{- 20} N$ 407. $An infinite wire has a circular bend of radius a, and carrying a current I as shown in figure. The magnitude of magnetic field at the origin O of the arc is given by:$ (1) $\frac{μ _{0}}{4 π} \frac{I}{a} (\frac{π}{2} + 1)$ (2) $\frac{μ _{0}}{4 π} \frac{I}{a} (\frac{3 π}{2} + 2)$ (3) $\frac{μ _{0}}{2 π} \frac{I}{a} (\frac{π}{2} + 2)$ (4) $\frac{μ _{0}}{4 π} \frac{I}{a} (\frac{3 π}{2} + 1)$ 408. $Figure shows two semicircular loops of radii R_{1} and R_{2} carrying current t . The magnetic field at the common centre ' O' is$ (1) $\frac{μ _{0} I}{4} (\frac{1}{R _{1}} + \frac{1}{R _{2}})$ (2) $\frac{μ _{0} l}{4} (\frac{1}{R _{1}} - \frac{1}{R _{2}})$ (3) $\frac{μ _{0} I}{2 π} (\frac{1}{R _{1}} + \frac{1}{R _{2}})$ (4) $\frac{μ _{0} I}{2 π} (\frac{1}{R _{1}} - \frac{1}{R _{2}})$ 409. $A and B are two infinitely long straight parallel conductors. C is another straight conductor of length 1 m kept parallel to A and B as shown in the figure. Then the force experienced by C is$ (1) $towards A equal to 0.6\times 1 0^{- 5} N$ (2) $towards B equal to 5.4\times 1 0^{- 5} N$ (3) $towards A equal to 5.4\times 1 0^{- 5} N$ (4) $towards B equal to 0.6\times 1 0^{- 5} N.$ 410. $A long straight wire with a circular cross-section having radius R, is carrying a steady current I. The current I is uniformly distributed across this cross-section. Then the variation of magnetic field due to current I with distance r (r < R) from its center will be$ (1) $B \propto r^{2}$ (2) $B \propto r$ (3) $B \propto \frac{1}{r ^{2}}$ (4) $B \propto \frac{1}{r}$ 411. $A cylindrical conductor of radius R is carrying constant current. The plot of the magnitude of the magnetic field, B with the distance, d from the center of the conductor, is correctly represented by the figure:$ (1) (2) (3) (4) 412. $Two tangent galvanometers A and B have coils of radii 8 cm and 16 cm respectively and resistance 8Ω each. They are connected in parallel with a cell of emf 4 V and negligible internal resistance. The deflections produced in the T.G's A and B are 30^{\circ} and 60^{\circ} respectively. If A has 2 turns, then B must have$ (1) $18 turns$ (2) $12 turns$ (3) $6 turns$ (4) $2 turns.$ 413. $A square loop of side 2 a, and carrying current I, is kept in XZ plane with its centre at origin. A long wire carrying the same current I is placed parallel to the z-axis and passing through the point (0, b, 0),(b>>a). The magnitude of the torque on the loop about z-axis is given by$ (1) $\frac{2 μ _{0} I ^{2} a ^{2}}{πb}$ (2) $\frac{μ _{0} I ^{2} a ^{2}}{2 πb}$ (3) $\frac{μ _{0} I ^{2} a ^{3}}{2 π b ^{2}}$ (4) $\frac{2 μ _{0} I ^{2} a ^{3}}{π b ^{2}}$ 414. $The figure shows a region of length ’ I ’ with a uniform magnetic field of 0.3 T in it and a proton entering the region with velocity 4 \times 10^{5} ms^{- 1} making an angle 60^{\circ} with the field. If the proton completes 10 revolution by the time it cross the region shown ’ l ’, is close to (mass of proton = 1.67 \times 10^{- 27} kg, charge of the proton = 1.6 \times 10^{- 19} C)$ (1) $0.22 m$ (2) $0.11 m$ (3) $0.88 m$ (4) $0.44 m$ 415. $When a proton is released from rest in a room, it starts with an initial acceleration a_{0} towards west. When it is projected towards north with a speed v_{0} it moves with an initial acceleration 3 a_{0} toward west. The electric and magnetic fields in the room are:$ (1) $\frac{m a _{0}}{e} west, \frac{2 m a _{0}}{e v _{0}} down$ (2) $\frac{m a _{0}}{e} east, \frac{3 m a _{0}}{e v _{0}} up$ (3) $\frac{m a _{0}}{e} east, \frac{3 m a _{0}}{e v _{0}} down$ (4) $\frac{m a _{0}}{e} west, \frac{2 m a _{0}}{e v _{0}} up$ 416. $A steady current l flows through a wire with one end at O and the other and extending upto infinity as shwon in the figure. The magnetic field at a point P, located at a distance d from O is$ (1) $\frac{μ _{0} l}{4 π dcos α} (1 - sin α)$ (2) $\frac{μ _{0} l}{2 πdcos α} (1 - sin α)$ (3) $\frac{μ _{0} l}{4 πd}$ (4) $\frac{μ _{0} l}{4 πdsin α} (1 - cos α)$ 417. $A current of 1 A is flowing along the sides of an equilateral triangle of side 4.5 \times 10^{- 2} m . The magnetic field at the centroid of the triangle is (μ_{0} = 4 π \times 10^{- 7} H / m)$ (1) $4 \times 10^{- 5} T$ (2) $2 \times 10^{- 5} T$ (3) $4 \times 10^{- 4} T$ (4) $2 \times 10^{- 4} T$ 418. $A thin ring of 10 cm radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of 40 πrad s^{- 1} about its axis, perpendicular to its plane. If the magnetic field at its centre is 3.8 \times 10^{- 9} T then the charge carried by the ring is close to (μ_{0} = 4 π \times 10^{- 7} N / A^{2}) .$ (1) $2 \times 10^{- 6} C$ (2) $3 \times 10^{- 5} C$ (3) $4 \times 10^{- 5} C$ (4) $7 \times 10^{- 6} C$ 419. $An isosceles triangular current carrying loop is kept perpendicularly in a uniform magnetic field B_{0} as shown in figure. The force on the loop due to magnetic field is$ (1) $I L B_{0} cosθ$ (2) $2 I L B_{0} cosθ$ (3) $0$ (4) $I L B_{0} sin θ$ 420. $One of the two identical conducting wires of length L is bent in the form of a circular loop and the other one into a circular coil of N identical turns. If the same current is passed in both, the ratio of the magnetic field at the central of the loop (B_{1}) to that at the centre of the coil (B_{C}), i . e, \frac{B _{L}}{B _{C}} will be$ (1) $N$ (2) $\frac{1}{N}$ (3) $N^{2}$ (4) $1/ N^{2}$