Moving Charges & Magnetism PYQs Set 15 (PDF)

Set 15 of 17 · Questions 421-450 of 499

In the print window choose “Save as PDF”. The file prints without a web address or date line.

Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 15 (Q421-450)
Scan or visit mereteacher.com for free PYQ practice, timed CBT tests, step-by-step solutions and BroBot AI. Answers and solutions are free with a sign-up.
421. $Two infinitely long wires each carrying the same current and pointing in + y direction are placed in the xy -plane, at x = - 2 cm and x = 1 cm . An electron is fired with speed U from the origin making an angle of + 45^{\circ} from the x -axis. The force on the electron at the instant it is fired is (B_{o}) is the magnitude of the field at origin due to the wire at x = 1 cm alone].$ (1) $\frac{- eUB _{o}}{2 2} (i - j)$ (2) $\frac{- eU B _{o}}{2} (i - j)$ (3) $\frac{- e ^{2} B _{o}}{2} (i - j)$ (4) $- eUB_{0} (ı - ȷ)$ 422. $A metallic rod of mass per unit length 0.5 kg m^{-1} is lying horizontally on a smooth inclined plane which makes an angle of 30º with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is:$ (1) $7.14 A$ (2) $11.32 A$ (3) $14.76 A$ (4) $5.98 A$ 423. $Two concentric coils each of radius equal to 2 πcm are placed right angles to each other. If 3 A and 4 A are the currents flowing through the two coils respectively. The magnetic induction (in Wbm^{- 2}) at the centre of the coils will be$ (1) $10^{- 5}$ (2) $7\times 1 0^{- 5}$ (3) $12\times 1 0^{- 5}$ (4) $5\times 1 0^{- 5}$ 424. $Two concentric coils of 20 turns each are placed in same place. Their radii are 30 cm and 60 cm and carry 0.4 A and 0.6 A currents respectively in opposite directions. The magnetic induction at the centre in tesla is \dots \dots ..$ (1) $\frac{8}{3} μ_{0}$ (2) $\frac{2}{3} μ_{0}$ (3) $\frac{5}{3} μ_{0}$ (4) $\frac{10}{3} μ_{0}$ 425. $Two concentric circular loops of radii r_{1} = 30 cm and r_{2} = 50 cm are placed in X-Y plane as shown in the figure. A current I = 7A is flowing through them in the direction as shown in figure. The net magnetic moment of this system of two circular loops is approximately:$ (1) $\frac{7}{2} k A m^{2}$ (2) $- \frac{7}{2} k A m^{2}$ (3) $7 k A m^{2}$ (4) $- 7 k A m^{2}$ 426. $A coil of n number of turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current of strength I is passed through the coil, the magnetic field at its centre is$ (1) $\frac{μ _{0} nI}{( b - a )} log_{e} \frac{a}{b}$ (2) $\frac{μ _{0} nI}{2 ( b - a )}$ (3) $\frac{2 μ _{0} nI}{b}$ (4) $\frac{μ _{0} n}{2 ( b - a )} log_{e} \frac{b}{a}$ 427. $A toroid with thick windings of N turns has inner and outer radii R_{1} and R_{2} respectively. If it carries certain steady current I, the variation of the magnetic field due to the toroid with radial distance is correctly graphed in$ (1) (2) (3) (4) 428. $A closely wound solenoid of 2000 turns and area of cross-section 1.5 \times 10^{- 4} m^{2} carries a current of 2.0 A. It is suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field 5 \times 10^{- 2} tesla making an angle of 30^{\circ} with the axis of the solenoid. The torque on the solenoid will be$ (1) $3 \times 10^{- 3} N m$ (2) $1.5 \times 10^{- 3} N m$ (3) $1.5 \times 10^{- 2} N m$ (4) $3 \times 10^{- 2} N m$ 429. $Two equal electric currents are flowing perpendicular to each other as shown in the figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the currents. Where do we expect the resultant magnetic field to be zero?$ (1) $On CD$ (2) $On AB$ (3) $On both OD and BO$ (4) $On both AB and CD$ 430. $A rectangular coil (Dimension 5 cm \times 2.5 cm with 100 turns, carrying a current of 3 A in the clock-wise direction, is kept centered at the origin and in the X - Z plane. A magnetic field of 1 T is applied along X -axis. If the coil is tilted through 45^{\circ} about Z -axis, then the torque on the coil is:$ (1) $0.38 Nm$ (2) $0.55 Nm$ (3) $0.42 Nm$ (4) $0.27 Nm$ 431. $Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show$ (1) $anti ferromagnetism$ (2) $no magnetic property$ (3) $diamagnetism$ (4) $paramagnetism.$ 432. $In the diagram, I_{1}, I_{2} are the strength of the currents in the loop and straight conductors respectively. OA = OB = R . The net magnetic field at the centre O is zero.Then the ratio of the currents in the loop and the straight conductors is$ (1) $π$ (2) $2 π$ (3) $1/ π$ (4) $1/2 π$ 433. $A moving coil galvanometer of resistance 100Ω is used as an ammeter using a resistance 0.1Ω . The maximum deflection current in the galvanometer is 100 μA . Find the minimum current in the circuit, so that ammeter shows maximum deflection?$ (1) $100.1 mA$ (2) $1000.1 mA$ (3) $10.01 mA$ (4) $1.01 mA$ 434. $Two long wires with no contact are placed perpendicular to each other, i_{1} and i_{2} are currents flowing through these wires, respectively. The magnetic force on a small length dl of the second wire situated at a distance l from first wire is proportional to$ (1) $i_{1} i_{2}$ (2) $i$ (3) $\frac{1}{i _{1} i _{2}}$ (4) $i^{2}$ 435. $Two long current carrying thin wires, both with current I, are held by insulating threads of length L and are in equilibrium as shown in the figure, with threads making an angle 'θ' with the vertical. If wires have mass λ per unit length then the value of I is : (g = gravitational acceleration)$ (1) $sin θ \frac{πλgL}{μ _{0} cosθ}$ (2) $2 sin θ \frac{πλgL}{μ _{0} cosθ}$ (3) $2 \frac{πgL}{μ _{0}} tan θ$ (4) $\frac{πλgL}{μ _{0}} tan θ$ 436. $A planar loop of wire rotates in a uniform magnetic field. Initially at t = 0, the plane of the loop is perpendicular to the magnetic field. If it rotates with a period of 10 s about an axis in its plane then the magnitude of induced emf will be maximum and minimum, respectively at :$ (1) $2.5 sec, 5 sec$ (2) $5 sec, 7.5 sec$ (3) $2.5 sec, 7.5 sec$ (4) $10 sec, 5 sec$ 437. $A particle of mass m and charge q has an initial velocity v \to= v_{o} j^. If an electric field E \to= E_{o} i^and magnetic field B \to= B_{o} i^act on the particle, its speed will double after a time :$ (1) $t = \frac{m v _{0} 3}{qE}$ (2) $t = \frac{m v _{0} 2}{qE}$ (3) $t = \frac{m v _{0}}{qE}$ (4) $t = \frac{m v _{0}}{2 qE}$ 438. $An insulating thin rod of length l has a linear charge density ρ (x) = ρ_{0} \frac{x}{l} on it. The rod is rotated about an axis passing through the origin (x = 0) and perpendicular to the rod. If the rod makes n rotations per second, then the time averaged magnetic moment of the rod is:$ (1) $πnρ l^{3}$ (2) $\frac{π}{3} nρ l^{3}$ (3) $\frac{π}{4} nρ l^{3}$ (4) $n ρ l^{3}$ 439. $A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be [NEET 2016]$ (1) $\frac{μ _{0} Ii}{2 π}$ (2) $\frac{2 μ _{0} IiL}{3 π}$ (3) $\frac{μ _{0} IiL}{2 π}$ (4) $\frac{2 μ _{0} Ii}{3 π}$ 440. $In a co-axial straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero:$ (1) $outside the cable$ (2) $inside the outer conductor$ (3) $inside the inner conductor$ (4) $in between the two conductors$ 441. $A single current carrying loop of wire carrying current I flowing in anticlockwise direction seen from + ve z direction and lying in xy plane in shown in figure. The plot of j component of magnetic field (By) at a distance 'a' (less than radius of the coil) and on yz plane vs z coordinate look like$ (1) (2) (3) (4) 442. $The resistance of an ammeter is 13 Ω and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt‐resistance is$ (1) $2 Ω$ (2) $0.2 Ω$ (3) $2 kΩ$ (4) $20 Ω .$ 443. $An electron projected perpendicular to a uniform magnetic field B moves in a circle. If Bohr's quantization is applicable, then the radius of the electronic orbit in the first excited state is:$ (1) $\frac{h}{π e B}$ (2) $\frac{2 h}{πeB}$ (3) $\frac{h}{2 πeB}$ (4) $\frac{4 h}{πeB}$ 444. $When a charge of 3 C is placed in uniform electric field, it experiences a force of 3000 N . Within this field, potential difference between two points separated by a distance of 1 cm is$ (1) $10 V$ (2) $90 V$ (3) $1000 V$ (4) $3000 V$ 445. $A particle ’ P ’ is formed due to a completely inelastic collision of particles ’ x ’ and ’ y ’ having de-Broglie wavelengths ’ γ_{x} ’, and ’ γ_{y} ’' respectively. If x and y were moving in opposite directions, then the de-Broglie wavelength of ’ P ’ is:$ (1) $\frac{γ _{x} γ _{y}}{γ _{x} + γ _{y}}$ (2) $\frac{γ _{x} γ _{y}}{γ _{x} - γ _{y}}$ (3) $γ_{x} - γ_{y}$ (4) $γ_{x} + γ_{y}$ 446. $A solenoid of length 0.4 m and having 500 turns of wire carries a current 3 A. A thin coil having 10 turns of wire and radius 0.1 m carries current 0.4 A. The torque required to hold the coil in the middle of the solenoid with its axis perpendicular to the axis of the solenoid is (μ_{0} = 4 π \times 1 0^{- 7} SI units, π^{2} = 10) (sin 9 0^{\circ} = 1)$ (1) $3 \times 1 0^{- 6} N m$ (2) $12 \times 1 0^{- 6} N m$ (3) $6 \times 1 0^{- 6} N m$ (4) $24 \times 1 0^{- 6} N m$ 447. $The magnetic field (B) inside a long solenoid having n, turns per unit length and carrying current I when iron core is kept in it is (μ_{0} = permeability of vacuum, χ = magnetic susceptibility)$ (1) $μ_{0} ∋ (1 - χ)$ (2) $μ_{0} n t^{'} γ$ (3) $μ_{0} n I^{2} (1 + χ)$ (4) $μ_{0} n I (1 + χ_{1})$ 448. $An alternating electric field, of frequency u, is applied across the dees (radius = R) of a cyclotron that is being used to accelerate protons (mass = m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by$ (1) $B = m νe and K = 2 m π^{2} v^{2} R^{2}$ (2) $B = \frac{2 πm ν}{e} and K = m^{2} π$ (3) $B = \frac{2 π m ν}{e} and K = 2 m π^{2} ν^{2} R^{2}$ (4) $B = \frac{m ν}{e} and K = m^{2} π νR2$ 449. $A charged particle is moving in a uniform magnetic field (2 i + 3 j) T. If it has an acceleration (α i - 4 j) m/s^{2}, then the value of α will be$ (1) $3$ (2) $6$ (3) $12$ (4) $2$ 450. $A particle of charge q and mass m is moving with a velocity - v i^(v \neq = 0) towards a large screen placed in the Y - Z plane at a distance d . If there is a magnetic field B = B_{0} k^, the minimum value of v for which the particle will not hit the screen is$ (1) $\frac{2 q d B _{0}}{m}$ (2) $\frac{q d B _{0}}{3 m}$ (3) $\frac{q d B _{0}}{2 m}$ (4) $\frac{q d B _{0}}{m}$