Moving Charges & Magnetism PYQs Set 17 (PDF)

Set 17 of 17 · Questions 481-499 of 499

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Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 17 (Q481-499)
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481. $A charge Q is uniformly distributed over the surface of non-condcting disc of radius R. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity ω. As a result of this rotation a magnetic field of induction B is obtained at the centre of the disc. if we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by the figure:$ (1) (2) (3) (4) 482. $Position of an ant (S in metres) moving in Y - Z plane is given by S = 2 t^{2} j + 5 k (where t is in second). The magnitude and direction of velocity of the ant at t = 1 s will be :$ (1) $16 m / s in y-direction$ (2) $4 m / s in x -direction$ (3) $9 m / s in z-direction$ (4) $4 m / s in y -direction$ 483. $The electrostatic force (F_{1}) and magnetic force (F_{2}) acting on a charge q moving with velocity v can be written :$ (1) $F_{1} = q E, F_{2} = q (V \times B)$ (2) $F_{1} = q B, F_{2} = q (B \times V)$ (3) $F_{1} = q E, F_{2} = q (B \times V)$ (4) $F_{1} = q V \cdot E, F_{2} = q (B \cdot V)$ 484. $A circular coil has moment of inertia 0.8 kgm^{2} around any diameter and is carrying current to produce a magnetic moment of 20 Am^{2} . The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of 4 T is applied along the vertical, it starts rotating, around its horizontal diameter. The angular speed the coil acquires after rotating by 60^{\circ} will be$ (1) $10 rad s^{- 1}$ (2) $10 π rad s^{- 1}$ (3) $13.16 rad s^{- 1}$ (4) $20 π rad s^{- 1}$ 485. $Uniform magnetic fields of different strengths (B_{1} and B_{2}), both normal to the plane of the paper exist as shown in the figure. A charged particle of mass m and charge q, at the interface at an instant, moves into the region 2 with velocity v and returns to the interface. It continues to move into region 1 and finally reaches the interface. What is the displacement of the particle during this movement along the interface? (Consider the velocity of the particle to be normal to the magnetic field and B_{2} > B_{1})$ (1) $\frac{mv}{q B _{1}} (1 - \frac{B _{1}}{B _{2}}) \times 2$ (2) $\frac{mv}{q B _{1}} (1 - \frac{B _{2}}{B _{1}}) \times 2$ (3) $\frac{mv}{q B _{1}} (1 - \frac{B _{2}}{B _{1}})$ (4) $\frac{mv}{q B _{1}} (1 - \frac{B _{1}}{B _{2}})$ 486. $A charge ' q ' moves with velocity ' v ' through electric (E) as well as magnetic field (B). Then the force acting on it is$ (1) $q (v \times B)$ (2) $q (B \times v)$ (3) $q(v\cdotB)$ (4) $q E + q (v \times B)$ 487. $Two short bar magnets of length 1 cm each have magnetic moments 1.20 A m^{2} and 1.00 A m^{2} respectively. They are placed on a horizontal table parallel to each other with their N poles pointing towards the South. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the result and horizontal magnetic induction at the mid - point O of the line joining their centers is close to (Horizontal component of earth’s magnetic induction is 3.6\times 1 0^{-5} Wb/ m^{2})$ (1) $3.6 \times 1 0^{-5} Wb/ m^{2}$ (2) $2.56 \times 1 0^{-4} Wb/ m^{2}$ (3) $3.50 \times 1 0^{-4} Wb/ m^{2}$ (4) $5.80 \times 1 0^{-4} Wb/ m^{2}$ 488. $An electron is allowed to move with constant velocity along the axis of current carrying straight solenoid. (A) The electron will experience magnetic force along the axis of the solenoid. (B) The electron will not experience magnetic force. (C) The electron will continue to move along the axis of the solenoid. (D) The electron will be accelerated along the axis of the solenoid (E) The electron will follow parabolic path-inside the solenoid. Choose the correct answer from the option given below:$ (1) $B, C and D only$ (2) $A and D only$ (3) $B and C only$ (4) $B and E only$ 489. $An electron, moving along the x -axis with an initial energy of 100 eV, enters a region of magnetic field B = (1.5 \times 10^{- 3} T) k at S (see figure). The field extends between x = 0 and x = 2 cm The electron is detected at the point Q on a screen placed 8 cm away from the point S . The distance d between P and Q (on the screen) is:(Electron's charge = 1.6 \times 10^{- 19} C mass of electron (= 9.1 \times 10^{- 31} kg)$ (1) $11.65 cm$ (2) $12.87 cm$ (3) $1.22 cm$ (4) $2.25 cm$ 490. $The magnetic moment of a diamagnetic atom is$ (1) $much greater than one$ (2) $1$ (3) $between zero and one$ (4) $equal to zero$ 491. $A rigid wire consists of a semicircular portion of radius R and two straight sections. The wire is partially immerged in a perpendicular magnetic field B = B_{0} j as shown in figure. The magnetic force on the wire if it has a current i is:$ (1) $- iBR j$ (2) $2 iBR j$ (3) $iBR j$ (4) $- 2 iBR j$ 492. $A current carrying rectangular loop PQRS is made of uniform wire. The length PR = QS = 5 cm and PQ = RS = 100 cm. If ammeter current reading changes from I to 2I, the ratio of magnetic forces per unit length on the wire PQ due to wire RS in the two cases respectively f_{PQ}^{I} : f_{PQ}^{2 I} is:$ (1) $1 : 2$ (2) $1 :4$ (3) $1 : 5$ (4) $1 : 3$ 493. $If number of turns, area and current through a coil is given by n, A and i respectively then its magnetic moment will be$ (1) $niA$ (2) $n^{2} iA$ (3) $ni A^{2}$ (4) $\frac{ni}{A}$ 494. $Given below are two statements: Statement (I): When currents vary with time, Newton's third law is valid only if momentum carried by the electromagnetic field is taken into account. Statement (II) : Ampere's circuital law does not depend on Biot-Savart's law. In the light of the above statements, choose the correct answer from the options given below:$ (1) $Both Statement I and Statement II are true$ (2) $Statement I is true but Statement II is false$ (3) $Both Statement I and Statement II are false$ (4) $Statement I is false but Statement II is true$ 495. $An infinitely long wire carrying 1 A current in the + Z direction is placed at (1 cm, 1 cm) . Another wire carrying 1 A in + x direction is placed at y = 1 cm . If the magnetic field due to this configuration at the origin is B . Let B_{0} be the magnitude of the field if only the wire at (1 cm, 1 cm) was present, then \frac{B}{B _{0}} is$ (1) $(\frac{1}{2}, - \frac{1}{2}, - 2)$ (2) $(\frac{1}{2}, \frac{1}{2}, - 1)$ (3) $(2, 2, - 2)$ (4) $(\frac{1}{2 2}, \frac{1}{2 2}, - \frac{1}{2})$ 496. $An observer at rest experiences an electric field due to a static charge. Later he starts moving away from it then the observer experiences.$ (1) $Only magnetic field$ (2) $Only electric field$ (3) $Electric and magnetic field$ (4) $No field at all$ 497. $The magnetic field due to current carrying circular loop of radius 6 cm at a point on the axis at a distance of 8 cm from centre is 27 μT . The magnetic field at the centre of the current carrying loop is.$ (1) $75 μT$ (2) $125 μT$ (3) $150 μT$ (4) $250 μT$ 498. $Tesla is the unit of$ (1) $electric field$ (2) $magnetic field$ (3) $electric flux$ (4) $magnetic flux.$ 499. $Tangent galvanometer is used to measure$ (1) $potential difference$ (2) $current$ (3) $resistance$ (4) $charge.$