Moving Charges & Magnetism PYQs Set 15 (PDF)

Set 15 of 19 · Questions 421-450 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 15 (Q421-450)
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421. $Two thick wires and two thin wires, all of same material and same length, form a square in three different ways P, Q and R as shown in the figure. With correct connections shown, the magnetic field due to the current flow, at the centre of the loop will be zero in case of$ (1) $Q and R only$ (2) $P and Q only$ (3) $P only$ (4) $P and R only$ 422. $A coil having N turns is wound tightly in the form of a spiral with inner and outer radii 'a' and 'b' respectively. Find the magnetic field at center, when a current I passes through coil:$ (1) $\frac{μ _{0} IN}{2 ( b - a )} log_{e} (\frac{b}{a})$ (2) $\frac{μ _{0} I}{8} (\frac{a + b}{a - b})$ (3) $\frac{μ _{0} I}{4 ( a - b )} (\frac{1}{a} - \frac{1}{b})$ (4) $\frac{μ _{0} I}{8} (\frac{a - b}{a + b})$ 423. $Find the magnetic field at the point P in figure. The curved portion is a semicircle connected to two long straight wires.$ (1) $\frac{μ _{0} i}{2 r} (1 + \frac{2}{π})$ (2) $\frac{μ _{0} i}{2 r} (1 + \frac{1}{π})$ (3) $\frac{μ _{0} i}{2 r} (\frac{1}{2} + \frac{1}{2 π})$ (4) $\frac{μ _{0} i}{2 r} (\frac{1}{2} + \frac{1}{π})$ 424. $A current carrying loop in the form of a right angle isosceles triangle ABC is placed in a uniform magnetic field acting along AB. If the magnetic force on the arm BC is F, the force on the arm AC is:$ (1) $- 2 F$ (2) $- F$ (3) $F$ (4) $2 F$ 425. $Two long current carrying conductors are placed parallel to each other at a distance of 8 cm between them. The magnitude of magnetic field produced at mid-point between the two conductors due to current flowing in them is 300µT. The equal current flowing in the two conductors is:$ (1) $30A in the same direction.$ (2) $30A in the opposite direction.$ (3) $60A in the opposite direction.$ (4) $300A in the opposite direction.$ 426. $A straight wire of length 50 cm carrying a current of 2.5 A is suspended in mid-air by a uniform magnetic field of 0.5 T (as shown in figure). The mass of the wire is (g = 10 m s^{- 2})$ (1) $100 gm$ (2) $125 gm$ (3) $62.5 gm$ (4) $250 gm$ 427. $If only \frac{1}{51}^{th} of the main current is to be passed through a galvanometer then the shunt required is R_{1} and if only \frac{1 ^{th}}{11} of the main voltage is to be developed across the galvanometer, then the resistance required R_{2} . Then \frac{R _{2}}{R _{1}}$ (1) $\frac{1}{. 500}$ (2) $\frac{50}{9}$ (3) $\frac{500}{3}$ (4) $500$ 428. $Two long parallel wires are separated by a distance of 2.5 cm . The force per unit length that each wire exerts on the other is 4 \times 10^{- 5} N / m and the wires repel each other. The current in one wire is 0.5 A . What is the current in the second wire? (Take μ_{0} = 4 π \times 10^{- 7} SI unit)$ (1) $12 A$ (2) $8 A$ (3) $6 A$ (4) $10 A$ 429. $A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is$ (1) $uniform throughout the pipe but not zero$ (2) $zero only along the axis of the pipe$ (3) $zero at any point inside the pipe$ (4) $maximum at the centre and minimum at the edges.$ 430. $Current ' I' is flowing in a conductor shaped as shown in the figure. The radius of the curved part is r and the length of straight portion is very large. The value of the magnetic field at the centre O will be$ (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) $\frac{μ _{0} I}{4 πr} (\frac{3 π}{2} - 1)$ 431. $A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B' at radial distances a/2 and 2a respectively, from the axis of the wire is [NEET 2016]$ (1) $\frac{1}{2}$ (2) $1$ (3) $4$ (4) $\frac{1}{4}$ 432. $A bar magnet of length ‘I’ and magnetic dipole moment ‘M’ is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be:$ (1) $\frac{3}{π} M$ (2) $\frac{2}{π} M$ (3) $\frac{M}{2}$ (4) $M$ 433. $Two long wires carrying current is 8 A and 6 A along x axes and y axes respectively. The magnetic field at the point (2 i + 4 j) is (Take μ_{0} = 4 π \times 10^{- 7} SI unit)$ (1) $1 \times 10^{- 6} T$ (2) $2 \times 10^{- 6} T$ (3) $1 \times 10^{- 7} T$ (4) $2 \times 10^{- 7} T$ 434. $A current carrying loop ABCD has two circular arcs AD and BC with radius 1 cm and 2 cm respectively as shown in the figure. The two arcs AD and BC subtend a common angle 30^{\circ} at the centre O . If the current flowing in the loop is \frac{1.2}{π} A, then the magnitude of net magnetic field at O is (Given μ_{0} = 4 π \times 10^{- 7})$ (1) $0.5 μT$ (2) $3 μT$ (3) $1 μT$ (4) $1.5 μT$ 435. $A galvanometer has a coil of resistance 100 ohm and gives a full scale deflection for 30 mA current. If it is work as a voltmeter of 30 volt range, the resistance required to be added will be$ (1) $900 Ω$ (2) $1800 Ω$ (3) $500 Ω$ (4) $1000 Ω .$ 436. $Two circular coils made from same wire but radius of 1^{st} coil is twice that of 2^{nd} coil. If magnetic field at their centres is same then ratio of potential difference applied across them is (1^{st}) to 2^{nd} coil)$ (1) $2$ (2) $3$ (3) $4$ (4) $6$ 437. $A charged particle of mass m and charge q moving under the influence of uniform electric field Ei \to and a uniform magnetic field B k \to follows a trajectory from point P to Q as shown in figure. The velocities at P and Q are respectively, v i \to and - 2 v j \to . Then which of the following statements (A, B, C, D) are the correct? (Trajectory shown is schematic and not to scale)$ (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) $Change in angular momentum w.r.t. origin is 2 maV$ 438. $A straight conductor carrying current i splits into two parts as shown in the figure. The radius of the circular loop is R . The total magnetic field at the centre P at the loop is$ (1) $Zero$ (2) $3 μ_{0} i /32 R, outward$ (3) $3 μ_{0} i /32 R, inward$ (4) $\frac{μ _{0} i}{2 R}, inward I$ 439. $A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane. If the current in the loop is i. The resultant magnetic field due to the two semicircular parts at their common center is$ (1) $\frac{μ _{0} i}{2 2 R}$ (2) $\frac{μ _{0} i}{2 R}$ (3) $\frac{μ _{0} i}{4 R}$ (4) $\frac{μ _{0} i}{2 R}$ 440. $A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F_{1}, F_{2} and F_{3} respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is$ (1) $(F_{3} - F_{1})^{2} - F_{2}^{2}$ (2) $F_{3} - F_{1} + F_{2}$ (3) $F_{3} - F_{1} - F_{2}$ (4) $(F_{3} - F_{1})^{2} + F_{2}^{2} .$ 441. $Hysteresis loops for two magnetic materials A and B are given below: These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use:$ (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) $A for electric generators and transformers.$ 442. $A current I is flowing through the loop. The direction of the current and the shape of the loop are as shown in the figure. The magnetic field at the center of the loop is \frac{μ _{0} I}{R} times ((MA = R, MB = 2 R, ∠ DMA = 90^{\circ})$ (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) $7/16, but into the plane of the paper.$ 443. $Proton with kinetic energy of 1 MeV moves from south to north. It gets an acceleration of 10^{12} m / s^{2} by an applied magnetic field (west to east). The value of magnetic field: (Rest mass of proton is 1.6 \times 10^{- 27} Kg)$ (1) $0.71 mT$ (2) $7.1 mT$ (3) $71 mT$ (4) $710 mT$ 444. $PQ and RS are long parallel conductors separated by certain distance. M is the midpoint between them (see the figure). The net magnetic field at M is B . Now, the current 2 A is switched off. The field at M now becomes$ (1) $2 B$ (2) $B$ (3) $B /2$ (4) $3 B$ 445. $An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of 10^{5} m / s parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the magnitude of the force experienced by the electron at that instant [NEET 2021]$ (1) $8 \times 10^{- 20} N$ (2) $4 \times 10^{- 20} N$ (3) $8 π \times 10^{- 20} N$ (4) $4 π \times 10^{- 20} N$ 446. $An infinite wire has a circular bend of radius a, and carrying a current I as shown in figure. The magnitude of magnetic field at the origin O of the arc is given by:$ (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) $\frac{μ _{0}}{4 π} \frac{I}{a} (\frac{3 π}{2} + 1)$ 447. $Two 10 cm long, straight wires, each carrying a current of 5A are kept parallel to each other. If each wire experienced a force of 1 0^{- 5} N, then separation between the wires is_________cm.$ 448. $Two identical circular wires of radius 20 cm and carrying current 2 A are placed in perpendicular planes as shown in figure. The net magnetic field at the centre of the circular wires is________x 10-8T. (Take π = 3 14)$ 449. $A straight wire AB of mass 40 g and length 50 cm is suspended by a pair of flexible leads in uniform magnetic field of magnitude 0.40 T as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is_____A. (Take g = 10 m s^{- 2}).$ 450. $A deuteron and a proton moving with equal kinetic energy enter into to a uniform magnetic field at right angle to the field. If r_{d} and r_{p} are the radii of their circular paths respectively, then the ratio \frac{r _{d}}{r _{p}} will be x : 1 where x is______.$