Title 4.MOVING CHARGES AND MAGNETISM - Questions.pdf ✅

4.MOVING CHARGES AND MAGNETISM (1.)A wire of length 2 m carrying a current of 1 A is bent to form a circle, the magnetic moment of the coil is (a.) 2π Am2 (b.) 1 π Am2 (c.) π Am2 d) 2 π Am2 (2.)A conducting loop carrying a current I is placed in a uniform magnetic field pointing into the plane of the paper as shown. The loop will have a tendency to (a.) Contract (b.) Expand (c.) Move towards +ve x − axis d) Move towards −ve x − axis (3.)A coil of 100 turns and area 2 × 10−2m2 , pivoted about a vertical diameter in a uniform magnetic field carries a current of 5A. When the coil is held with its plane in North-South direction, it experience a torque of 0.3 Nm. When the plane is in East-West direction the torque is 0.4 Nm. The value of magnetic induction is (Neglect earth’s magnetic field) (a.) 0.2 T (b.) 0.3 T (c.) 0.4 T d) 0.05 T (4.)The figure shows certain wire segments joined together to form a coplanar loop. The loop is placed in a perpendicular magnetic field in the direction going into the plane of the figure. The magnitude of the field increases with time. I1 and I2 are the currents in segment ab and cd. Then, (a.) I1 > I2 (b.) I1 < I2 (c.) I1 is in the direction ba and I2 is in the direction cd d)I1 is in the direction ab and I2 is in the direction dc (5.)Two circular coils are made of two identical wires of same length. If the number of turns of two coils are 4 and 2, then the ratio of magnetic induction at centres will be zero (a.) 4 : 1 (b.) 2 : 1 (c.) 1 : 2 d) 1 : 1 (6.)A triangular loop of side l carries a current I. It is placed in a magnetic field B such that the plane of the loop is in the direction of B. The torque on the loop is (a.) Zero (b.) IBl (c.) √3 2 Il 2B 2 d) √3 4 IBl 2 (7.)An electron (e = 1.6 × 10−19C) moves in a circular orbit of radius 1.42 cm with a speed of 105 ms −1 in presence of magnetic field of 4 × 10−2T. If the mass of electron is 9.1 × 10−31 kg the energy gained by the electron in going one round the circular orbit is (a.) zero (b.) 4.54 × 10−28 J (c.) 9.08 × 10−28 J d) 28.55 × 10−28 J (8.)An ammeter has resistance R0 and range I. What resistance should be connected in parallel with it to increase its range by nI? (a.) R0/(n − 1) (b.) R0/(n + 1) (c.) R0/n d) None of these (9.)A vertical wire carrying a current in the upward direction is placed in horizontal magnetic field directed towards north. The wire will experience a force directed towards (a.) North (b.) South (c.) East d) West (10.)In a square loop PQRS made with a wire of cross-section current i enters from point P and leaves from point S. The magnitude of magnetic field induction at the centre O of the square is I X
(a.) μ0 4π 2√2i a (b.) μ0 4π 4√2i a (c.) μ0 4 2√2i a d) zero (11.)Two short bar magnets with magnetic moments 400 ab-amp cm2 and 800 ab-amp cm2 are placed with their axis in the same straight line with similar poles facing each other and with their centers at 20 cm from each other. Then the force of repulsion is (a.) 12 dyne (b.) 6 dyne (c.) 800 dyne d) 150 dyne (12.)A straight wire of length 0.5 metre and carrying a current of 1.2 ampere is placed in a uniform magnetic field of induction 2 tesla. The magnetic field is perpendicular to the length of the wire. The force on the wire is (a.) 2.4 N (b.) 1.2 N (c.) 3.0 N d) 2.0 N (13.)The resultant magnetic moment of neon atom will be (a.) Infinity (b.) μB (c.) Zero d) μB/2 (14.)An equilateral triangle of side l is formed from a piece of wire of uniform resistance. The current i is fed as shown in the figure. The magnitude of the magnetic field as its centre O is (a.) √3μ0i 2πl (b.) 3√2μ0i 2πl (c.) μ0i 2πl d) zero (15.)Magnetic dipole moment of a rectangular loop is (a.) Inversely proportional to current in loop (b.) Inversely proportional to area of loop (c.) Parallel to plane of loop and proportional to area of loop d) Perpendicular to plane of loop and proportional to area of loop (16.)An electron (charge q coulomb) enters a magnetic field of H weber/m2 with a velocity of vm/s in the same direction as that of the field. The force on the electron is (a.) Hqv newtons in the direction of the magnetic field (b.) Hqv dynes in the direction of the magnetic field (c.) Hqv newtons at right angles to the direction of the magnetic field d) Zero (17.)Two wires of same length are shaped into a square and a circle. If they carry same current, ratio of the magnetic moment is (a.) 2 ∶ π (b.) π ∶ 2 (c.) π ∶ 4 d) 4 ∶ π (18.)A circular coil is in y-z plane with centre at origin. The coil is carrying a constant current. Assuming direction of magnetic field at x = −25 cm to be positive direction of magnetic field, which of the following graphs shows variation of magnetic field along x-axis (a.) (b.) (c.) d) (19.)A charge particle of mass m and charge q enters a region of uniform magnetic field B perpendicular of its velocity v. The particle initially at rest was accelerated by a potential difference V (volts) before it entered the region of magnetic field. What is the diameter of the circular path B O x B O x B O x B O x
followed by the charged particle in the region of magnetic field? (a.) 2 B √ mV q (b.) 2 B √ 2mV q (c.) B√ 2mV q d) B q √ 2mV B (20.)Which of the following gives the value of magnetic field according to Biot-Savart’ law (a.) i∆l sin θ r 2 (b.) μ0 4π i∆l sin θ r (c.) μ0 4π i∆l sin θ r 2 d) μ0 4π i∆l sinθ (21.)The velocity of two α-particles A and B in a uniform magnetic field is in the ratio of 1 : 3. They move in different circular orbits in the magnetic field. The ratio of radius of curvatures of their paths is (a.) 1 : 2 (b.) 1 : 3 (c.) 3 : 1 d) 2 : 1 (22.)Two very long, straight, parallel wires carry steady current i and − i resepectively. The distance between the wires is d. At a certain instant of time, a point charge q is at a point equidistant from the two wires, in the plane of the wires. Its instantaneous magnitude of the force due to the magnetic field acting on the charge at this instant is (a.) μ0iqv 2πd (b.) μ0iqv πd (c.) 2μ0 iqv πd d) zero (23.)A wire along x-axis carries a current 3.5 A. Find the force in newton on a 1 cm section of the wire exerted by a magnetic field B⃗ = (0.74 ĵ+ 0.36 k̂) T. (a.) (1.26 k̂ − 2.59 ĵ)10−2 N (b.) (−1.26 k̂ + 2.59 ĵ) × 10−2 N (c.) (−2.59 k̂ + 1.26 ĵ) × 10−2 N d) (2.59 k̂ − 1.26 ĵ) × 10−2 N (24.)Current i0 is passed through a solenoid of length l having number of turns N when it is connected to a DC source. A charged particle with charge q is projected along the axis of the solenoid with a speed v0. The velocity of the particle in the solenoid (a.) Increases (b.) Decreases (c.) Remain same d) Becomes zero (25.)Energy in a current carrying coil is stored in the form of (a.) Electrical energy (b.) Magnetic field (c.) Heat d) None of these (26.)Current i is carried in a wire of length L. If the wire is turned into a circular coil, the maximum magnitude of torque in a given magnetic field B will be (a.) LiB 2 2 (b.) Li 2B 2 (c.) L 2iB 4π d) Li 2B 4π (27.)The proton is energy 1 MeV describes a circular path in plane at right angles to a uniform magnetic field of 6.28 × 10−4 T. The mass of the proton is 1.7 × 10−27 kg. The cyclotron frequency of the proton is very nearly equal to (a.) 107 Hz (b.) 105Hz (c.) 106 Hz d) 104 Hz (28.)A particle of mass m, charge Q and kinetic energy T enters a transverse uniform magnetic field of induction B⃗ . After 3 seconds the kinetic energy of the particle will be (a.) T (b.) 4 T (c.) 3 T d) 2 T (29.)The direction of magnetic lines of forces close to a straight conductor carrying current will be (a.) Along the length of the conductor (b.) Radially outward (c.) Circular in a plane perpendicular to the conductor d) Helical (30.)The force between two parallel current carrying wires is independent of (a.) Their distance of separation (b.) The length of the wires (c.) The magnitude of currents d) The radii of the wires (31.)In order to increase the sensitivity of a moving coil galvanometer, one should decrease (a.) The strength of its magnet (b.) The torsional constant of its suspension (c.) The number of turns in its coil d) The area of its coil
(32.)Biot-Savart’s law may be represented in vector form as (a.) dB = μ0 4π i dl×r r 3 (b.) dB = μ0 4π i dl × r (c.) dB = μ0 4π i dl×r r 2 d) dB = μ0 4π i dl×r r (33.)A deutron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 m in a plane perpendicular to magnetic field B⃗ . The kinetic energy of the proton that describes a circular orbit of radius 0.5 m in the same plane with the same B⃗ is (a.) 200 keV (b.) 100 keV (c.) 50 keV d) 25 keV (34.)A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segment PS, SR and RQ are F1, F2 and F3 respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is (a.) √(F3 − F1 ) 2 − F2 2 (b.) F3 + F1 − F2 (c.) F3 − F1 + F2 d) √(F3 − F1 ) 2 + F2 2 (35.)A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particle will (a.) Get deflected vertically upwards (b.) Move in a circular orbit with its speed increased (c.) Move in a circular orbit with its speed unchanged d) Continue to move due east (36.)A man carrying suitable instruments for measuring electric and magnetic field passes by a stationary electron with velocity V. Then these instruments will note (a.) Electric field (b.) Magnetic field (c.) Both a and b d) None of these (37.)A straight wire carrying current i is turned into a circular loop. If the magnitude of magnetic moment associated with it in MKS unit is M, the length of wire will be (a.) 4π M (b.) √ 4 π M i (c.) √ r π i M d) M π 4 i (38.)In a mass spectrometer used to measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant, the ratio ( charge on the ion mass of the ion ) will be proportional (a.) 1/R (b.) 1/R 2 (c.) R 2 d) R (39.)Which of the following graphs represent variation of magnetic field B with distance r for a straight long wire carrying current? (a.) (b.) (c.) d) (40.)An electron (q = 1.6 × 10−19 C) is moving at right angle to the uniform magnetic field 3.534×10−5 T. The time taken by the electron to complete a circular orbit is (a.) 2μs (b.) 4μs B Distance (r) B Distance (r) B Distance (r) B Distance (r)