Lorentz Force & Charged Particle Motion — Practice Questions

Free NEET Physics multiple-choice questions on Lorentz Force & Charged Particle Motion. Attempt each question and reveal the answer with a full explanation.

A magnetic needle is kept in a non-uniform magnetic field. It experiences: A force and a torque A force but no torque A torque but no force Neither a force nor a torque The angle of dip at a place where the horizontal component of the earth's magnetic field is equal to the vertical component is: 45 0 30 60 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 3a 0 toward west. The electric and magnetic fields in the room are ma 0 e west, 2ma 0 ev 0 up ma 0 e west, 2ma 0 ev 0 down ma 0 e east, 3ma 0 ev 0 up ma 0 e east, 3ma 0 ev 0 down Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that ‘O’ is their common point for the two. The wires carry I 1 and I 2 currents respectively. Point ‘P’ is lying at distance ‘d’ from ‘O’ along a direction perpendicular to the plane containing the wires. The magnetic field at the point ‘P’ will be :- 0 2 d ( I 1 I 2 ) 0 2 d (I 1+I 2) 0 2 d [I 1 2-I 2 2] 0 2 d [I 1 2+I 2 2] 1/2 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 :- 2 0Ii 3 0Ii 2 2 0IiL 3 0IiL 2 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 : 1 4 1 2 1 4 An electron moves straight inside a charged parallel plate capacitor of uniform charge density . The space between the plates is filled with uniform magnetic field of intensity B , as shown in the figure. Neglecting effect of gravity, the time of straight line motion of the electron in the capacitor is : 0 ,lB 0 ,lB 0 ,B 0 ,B 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 30° 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 14.76 A 5.98 A 7.14 A 11.32 A A cylindrical conductor of radius R is carrying a constant current. The plot of the magnitude of the magnetic field. B with the distance d from the centre of the conductor, is correctly represented by the figure : 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. 8 10 -20 N 4 10 -20 N 8 10 -20 N 4 10 -20 N A thick current carrying cable of radius 'R' carries current 'I' uniformly distributed across its cross-section. The variation of magnetic field B(r) due to the cable with the distance ' r ' from the axis of the cable is represented by In the product F = q( v B ) = q v (B i + B j + B 0 k ) For q = 1 and v = 2 i + 4 j + 6 k and F = 4 i - 20 j + 12 k What will be the complete expression for B ? -6 i -6 j -8 k 8 i +8 j -6 k 6 i +6 j -8 k -8 i -8 j -6 k An electron is moving in a circle of radius r in a uniform magnetic field B . If the speed of the electron is doubled, the time period of its revolution will: Remain the same Be doubled Be halved Become four times Given below are two statements Statement I : Biot-Savart’s law gives us the expression for the magnetic field strength of an infinitesimal current element (Idl) of a current carrying conductor only. Statement II : Biot-Savart’s law is analogous to Coulomb’s inverse square law of charge q , with the former being related to the field produced by a scalar source, Idl while the latter being produced by a vector source, q . In light of above statements choose the most appropriate answer from the options given below Both Statement I and Statement II are incorrect Statement I is correct and Statement II is incorrect Statement I is incorrect and Statement II is correct Both Statement I and Statement II are correct A very long conducting wire is bent in a semi-circular shape from A to B as shown in figure. The magnetic field at point P for steady current configuration is given by 0 i 4R pointed into the page 0 i 4R pointed away from the page 0 i 4R [1- 2 ] pointed away from page 0 i 4R [1- 2 ] pointed into the page An electron (mass 9 10 -31 kg and charge 1.6 10 -19 C ) moving with speed c/100 ( c = speed of light) is injected into a magnetic field B of magnitude 9 10 -4 T perpendicular to its direction of motion. We wish to apply an uniform electric field E together with the magnetic field so that the electron does not deflect from its path. Then (speed of light c = 3 10 8 ms -1 ) E is parallel to B and its magnitude is 27 10 4 V m -1 E is perpendicular to B and its magnitude is 27 10 4 V m -1 E is perpendicular to B and its magnitude is 27 10 2 V m -1 E is parallel to B and its magnitude is 27 10 2 V m -1 A 100-turn closely wound circular coil of radius 5 cm has a magnetic field of 3.14 10 -3 T at its centre. The current flowing through the coil, and the magnitude of the magnetic moment of this coil are, respectively : (Take 0 = 4 10 -7 T m/A) 2.5 A, 20 A m 2 2 A, 4 A m 2 2.5 A, 2 A m 2 2 A, 10 A m 2 The figure given below shows a long straight solid wire of circular cross-section of radius 'a' carrying steady current I . The current I is uniformly distributed across its cross-section. The plot which correctly represents the variation of magnetic field (B) with distance (r) from the axis of the conductor in the region is : An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 × 10 -2 T. If the value of e/m is 1.76 × 10 11 C/kg, the frequency of revolution of the electron is: 1 GHz 100 MHz 62.8 MHz 6.28 GHz A particle of mass m and charge q is projected into a uniform magnetic field B with a velocity v at an angle of 30 ∘ with the field. The pitch of the helical path is: √3 π m v / q B π m v / q B 2π m v / q B √3 m v / q B A bar magnet has a magnetic moment M and length L . If it is bent into a semi-circular shape, its new magnetic moment will be: 2M/ M/ M 2M A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be (Angle subtended at center is 60 ): 3M/ M/ 2M/ M A wire of length L carries a current I along the x-axis. A magnetic field exists in the region given by B = B 0( j + k ) . The magnitude of the magnetic force acting on the wire is: 2 I L B 0 I L B 0 2 I L B 0 Zero A compass needle is placed in a horizontal plane. At which of the following locations will it point in a random direction? Magnetic poles Magnetic equator Geographic poles 45 latitude A magnetic needle of magnetic moment 6.7 10 -2 Am 2 and moment of inertia 7.5 10 -6 kg m 2 is performing simple harmonic oscillations in a magnetic field of 0.01 T. The time period of oscillation is: 0.66 s 0.11 s 2.1 s 1.2 s A metallic rod of mass per unit length is lying horizontally on a smooth inclined plane which makes an angle of with the horizontal. A magnetic field B acts vertically upwards. The current I required to keep the rod stationary on the plane is: g B g B g B g B Two electrons are moving parallel to each other with the same velocity v . The ratio of the magnetic force to the electric force between them is: v 2/c 2 v/c c 2/v 2 c/v The magnetic field B at a distance r from a point charge q moving with velocity v is given by: 0 4 q( v r ) r 3 0 4 q( v r ) r 3 0 4 q( r v ) r 2 0 4 qv r 2 A long straight wire carries a current I . A square loop of side a is placed in the same plane such that two of its sides are parallel to the wire. If the nearest side is at a distance a from the wire, the net force on the loop is: 0 I 2 / (4 ) attractive 0 I 2 / (4 ) repulsive 0 I 2 / (2 ) attractive Zero If an electron is moving parallel to a current-carrying straight wire in the same direction as the current, the electron will: Be repelled from the wire Be attracted towards the wire Continue to move parallel without deflection Stop moving A charge q is moving with a velocity v 1 = 1 i m/s in a magnetic field B and experiences a magnetic force F 1 = q(- j + k ) N. When the same charge moves with velocity v 2 = 1 j m/s, it experiences a force F 2 = q( i - k ) N. The magnetic field B is: i + j + k i - j + k - i + j - k i + j - k A cyclotron is used to accelerate protons. If the radius of the dees is 0.5 m and the magnetic field is 1.5 T, the maximum kinetic energy of the protons (mass = 1.67 10 -27 kg) is approximately: 27 MeV 13 MeV 54 MeV 7 MeV A metallic rod of mass per unit length 0.5 kg/m is lying horizontally on a smooth inclined plane which makes an angle of 30 with the horizontal. A magnetic field of strength 0.25 T is acting vertically upwards. If the current in the rod is I , what is the value of I for which the rod remains stationary? 11.32 A 7.5 A 5.8 A 15.2 A A proton, a deuteron and an alpha-particle, having the same kinetic energy, are moving in circular orbits in a constant magnetic field. If r p, r d, r are their radii respectively, then: r d = r > r p r p = r d = r r > r d > r p r p > r d = r A magnetic dipole is placed in a non-uniform magnetic field. It experiences: Both a force and a torque Only a force Only a torque Neither a force nor a torque A coil in the shape of an equilateral triangle of side is suspended between the pole pieces of a permanent magnet such that B is in plane of the coil. If due to a current i in the triangle a torque acts on it, the side of the triangle is- 2 3 ( Bi ) 1 3 Bi 2 ( 3 Bi ) 1/2 2 3 ( Bi ) 1/2 A model for quantized motion of an electron in a uniform magnetic field B states that the flux passing through the orbit of the electron is n(h/e) where n is an integer, h is Planck’s constant and e is the magnitude of electron’s charge. According to the model, the magnetic moment of an electron in its lowest energy state will be ( m is the mass of the electron) heB 2 m he m he 2 m heB m The maximum velocity to which a proton can be accelerated in a cyclotron of radius R and magnetic field B is: qBR/m qB/mR qB 2R/m qR/mB A current-carrying wire is placed in a uniform magnetic field B such that it makes an angle of 30 with the field. If the length of the wire is L and the current is I , the force experienced by the wire is: BIL/2 BIL 3 BIL/2 Zero A particle of charge q and mass m is moving with a velocity v in a magnetic field B . The magnetic force does no work on the particle because: The force is always perpendicular to the velocity. The force is always parallel to the velocity. The magnetic field is uniform. The particle is moving in a circle. A cyclotron is used to accelerate charged particles. If the frequency of the applied AC voltage is f , then the frequency of revolution of the particle must be: f 2f f/2 4f The gyromagnetic ratio of an electron revolving in a circular orbit is given by: e/2m e/m 2e/m m/e A square loop of wire carrying current I is placed in a uniform magnetic field B . The force on the loop is: Always zero Non-zero and constant Zero only if the plane is perpendicular to B Maximum when the plane is parallel to B At a place, the horizontal component of Earth's magnetic field is B H and the vertical component is B V . If the angle of dip is 60 , then: B V = 3 B H B H = 3 B V B V = B H B V = 3 B H In a region of space, the magnetic field is zero. Which of the following must be true for a particle moving in this region? Its velocity vector remains constant. Its kinetic energy changes. It must be at rest. It follows a parabolic path. A charged particle moves through a magnetic field perpendicular to its direction. Then: The kinetic energy of the particle remains constant The momentum of the particle remains constant The velocity of the particle remains constant The acceleration of the particle remains constant A particle of mass m , charge q and kinetic energy T enters a transverse uniform magnetic field of induction B . After 3 seconds, the kinetic energy of the particle will be: T 4T 3T 2T Under the influence of a uniform magnetic field, a charged particle moves in a circle of radius R with constant speed v . The time period of the motion is: Independent of v and R Proportional to v and R Proportional to v and independent of R Independent of v and proportional to R A square current loop of side L and current I is placed in a uniform magnetic field B such that the plane of the loop is perpendicular to the direction of B . The net force on the loop is: Zero ILB 4ILB 2ILB In a certain region of space, electric field E and magnetic field B are perpendicular to each other. An electron enters perpendicularly to both the fields and moves undeflected. The velocity of the electron is: E/B B/E E B E 2/B If the velocity of a charged particle is perpendicular to a uniform magnetic field, its path will be: A circle A straight line A parabola A helix A proton enters a uniform magnetic field with a velocity directed at an angle of 45 to the field lines. The path of the proton will be a: Helix Circle Straight line Parabola The force on a current-carrying wire of length L in a magnetic field B is maximum when the angle between the wire and the field is: 90 0 45 180 A charged particle is moving in a uniform magnetic field B . The work done by the magnetic force on the particle is: Zero Always positive Always negative Depends on the angle between v and B The angle between the magnetic meridian and the geographic meridian at a place is called: Magnetic Declination Magnetic Dip Inclination Horizontal Intensity In a velocity selector, a beam of particles passes undeflected through crossed electric field E and magnetic field B . The speed of the particles is: E/B B/E E/B E 2/B A charged particle enters a uniform magnetic field at an angle of 0 with the field direction. Its path will be: A straight line A circle A helix A parabola Two long straight parallel wires carry currents I and I in opposite directions. The force between them per unit length is: Repulsive, 0 I 2 2 d Attractive, 0 I 2 2 d Repulsive, 0 I 2 d Zero A charge q is moving with velocity v in the presence of magnetic field B and electric field E . If the net force on the charge is zero, then: v = E/B and E ⊥ B v = B/E v = EB v = E+B The path of a charged particle moving in a uniform magnetic field can be a circle or a helix. Which component of the velocity remains constant in both cases? Speed Velocity vector Momentum vector Acceleration A particle of charge q is moving with velocity v along the positive x-axis. A magnetic field B is directed along the positive y-axis. The Lorentz force on the particle is directed along: Positive z-axis Negative z-axis Positive y-axis Negative x-axis A charged particle moves through a magnetic field in a direction perpendicular to it. Which of the following quantities of the particle will change? Velocity Speed Kinetic energy Mass A particle of mass m and charge q is moving in a region where uniform electric field E and magnetic field B are present. The particle is projected with velocity v perpendicular to both fields. If the particle continues to move in a straight line with constant velocity, then: v = E/B v = B/E v = E/B v = E 2/B The gyro-magnetic ratio of an electron in an atom is independent of: Orbit radius Mass of electron Charge of electron None of these A particle of charge q and mass m is moving with a velocity v = v i in a magnetic field B = B j . The radius of the circular path is: mv/qB qB/mv mB/qv vB/mq Which of the following elements of Earth's magnetic field is zero at the magnetic equator? Angle of dip Horizontal component Declination Total intensity In a cyclotron, the resonance condition is reached when: The oscillator frequency is equal to the cyclotron frequency The velocity is equal to the speed of light The magnetic field is zero The kinetic energy is maximum An electron moves in a circular orbit with a uniform speed v . It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to : v B v B B v B v When a charged particle moving with velocity V is subjected to a magnetic field of induction B , the force on it is non-zero. This implies the:- Angle between V and B is necessary 90 Angle between V and B can have at value other than 90 Angle between V and B can have at value other than zero and 180 Angle between V and B is either zero or 180 A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move in a circular orbit along a parabolic path along a straight line in an elliptical orbit. A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment is given by qvR 2 qvR 2/2 qvR qvR/2 Under the influence of a uniform magnetic field a charged particle is moving in a circle of radius R with constant speed v. The time period of the motion depends on both R and v is independent of both R and v depends on R and not on v depends on v and not on R The magnetic force acting on a charged particle of charge -2 c in a magnetic field of 2T acting in y direction, when the particle velocity is (2 i +3 j ) 10 6 ms -1 , is : 8N in z direction 8N in -z direction 4N in z direction 8N in y direction Under the influence of a uniform magnetic field, a charged particle moves with constant speed V in a circle of radius R. The time period of rotation of the particle : Depends on both v and R Depends on v and not on R Depends on R and not on v Is independent of both v and R A uniform magnetic field of 0.3 T is established along the positive Z-direction. A rectangular loop in XY plane of sides 10 cm and 5 cm carries a current of I =12 , A as shown. The torque on the loop is : +1.8 10 -2 , i , NM -1.8 10 -2 , j , NM Zero -1.8 10 -2 , i , NM Ionized hydrogen atoms and -particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r H : r will be : 1 : 4 2 : 1 1 : 2 4 : 1 An electron is projected into a uniform magnetic field B with a velocity v at right angles to the field. If the speed is doubled and the field is halved, the radius of the circular path will: Quadruple Double Stay the same Be halved A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the centre of the solenoid is : ( 0 = 4 10 -7 T m A -1 ) 3.14 10 -4 T 6.28 10 -5 T 3.14 10 -5 T 6.28 10 -4 T A long solenoid of radius 1 mm has 100 turns per mm. If 1 A current flows in the solenoid, the magnetic field strength at the centre of the solenoid is 12.56 10 -2 T 12.56 10 -4 T 6.28 10 -4 T 6.28 10 -2 T From Ampere’s circuital law for a long straight wire of circular cross-section carrying a steady current, the variation of magnetic field in the inside and outside region of the wire is A linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the outside region. A linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1 r dependence for the outside region. A linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one for and outside region. Uniform and remains constant for both the regions. A wire carrying a current I along the positive x -axis has length L . It is kept in a magnetic field B =(2 i +3 j -4 k ) T. The magnitude of the magnetic force acting on the wire is 3 ,IL 5 ,IL 5 ,IL 3 ,IL A tightly wound 100 turns coil of radius 10 cm carries a current of 7 A. The magnitude of the magnetic field at the centre of the coil is (Take permeability of free space as 4 10 -7 SI units): 44 mT 4.4 T 4.4 mT 44 T A proton and an alpha particle move in circular orbits in a uniform magnetic field with the same speed. If the radius of the proton's orbit is R p and that of the alpha particle is R , what is the ratio R p/R ? 1/2 1 2 1/4 In a cyclotron, the time taken by an ion to describe a semicircular path is: Independent of speed and radius Dependent on speed Dependent on radius Dependent on both speed and radius The magnetic moment of an electron revolving in a circular orbit of radius r with speed v is: evr/2 evr e/vr 2evr A sensitive magnetic compass needle is placed at the magnetic poles of the Earth. In which direction will it point? It can stay in any direction. North-South direction. East-West direction. Vertically upwards. A proton is moving in a region of uniform magnetic field B and uniform electric field E . If E and B are parallel and the proton is projected parallel to them, its path will be: Straight line Circle Helix Parabola The 'Bohr Magneton' is the magnetic moment associated with an electron in the: First orbit of hydrogen atom Nucleus of any atom Outer shell of a metal Valence shell of a halogen A proton and an electron enter a uniform magnetic field with the same momentum p perpendicular to the field. Which of the following is true? Both describe circles of the same radius. The electron describes a circle of smaller radius. The proton describes a circle of smaller radius. Both describe straight lines. An electron moves in a circular orbit of radius r with a frequency f . The magnetic field at the center of the orbit is: 0 e f 2r 0 e f r 0 e 2rf 0 f 2er An electron is moving in the North direction. It experiences a force in the vertically upward direction due to a magnetic field. The direction of the magnetic field is towards: East West South North If the magnetic dipole moment of an atom is M and the angular momentum is L , the ratio M/L for an electron is: e/2m e/m 2e/m m/2e A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It will: Stay in any position Stay in North-South direction only Stay in East-West direction only Become vertical In a cyclotron, the maximum kinetic energy of the accelerated particle is given by (where R is the radius of the dees): q 2 B 2 R 2 2m q B R 2m q B 2 R 2 2m 2 q 2 B R 2m The magnetic moment of an electron revolving in the n th Bohr orbit is proportional to: n n 2 1/n n 3 An electron of mass m and charge e is accelerated from rest through a potential difference V and then enters a uniform magnetic field B acting normal to its direction of motion. The radius of the circular path is: 2mV eB 2 mV 2eB 2 2mV eB mV eB In a region of space, the magnetic field is B = B 0 k . A particle of mass m and charge q enters the region with velocity v = v 0 i + v 1 k . The path of the particle is a helix with a pitch given by: 2 m v 1 qB 0 2 m v 0 qB 0 m v 1 qB 0 2 m v 0 2 + v 1 2 qB 0 A rectangular loop of area A carrying current I is placed in a uniform magnetic field B . The torque on the loop is maximum when the angle between the plane of the loop and the magnetic field is: 0 90 45 180 A paramagnetic substance is placed in a non-uniform magnetic field. It tends to move from: Weaker to stronger part of the field Stronger to weaker part of the field Stronger to zero field Does not move A compass needle is placed in a non-uniform magnetic field. It experiences: both a force and a torque. a force but no torque. a torque but no force. neither a force nor a torque. An electron is moving with a speed of 10 7 m/s in a circular path of radius 0.5 cm in a uniform magnetic field. The magnitude of the magnetic field is (given e/m = 1.76 10 11 C/kg): 1.13 10 -2 T 1.13 10 -4 T 2.26 10 -2 T 0.56 10 -2 T A proton and an -particle enter a uniform magnetic field with the same kinetic energy. The ratio of the radii of their paths R p/R is: 1 : 1 1 : 2 2 : 1 1 : 4 An infinitely long straight conductor carries a current of 5 A. An electron is moving with a speed of 10 5 m/s parallel to the conductor at a distance of 20 cm from it. The magnitude of the force experienced by the electron is: 8 10 -20 N 4 10 -20 N 8 10 -19 N 4 10 -19 N An electron moves in a circle of radius r with constant speed v . The magnetic field B at the center of the circle is: 0 ev 4 r 2 0 ev 2 r 2 0 ev r 2 0 e 4 r v A cyclotron's oscillator frequency is 10 MHz. What should be the operating magnetic field for accelerating protons? (Mass of proton = 1.67 10 -27 kg): 0.66 T 0.33 T 1.25 T 1.00 T An electron and a proton with the same kinetic energy enter a uniform magnetic field perpendicularly. The ratio of the radii of their circular paths ( r e / r p ) is: m e / m p m e / m p m p / m e 1 A charged particle is moving in a region where a uniform electric field E and a uniform magnetic field B are parallel to each other. If the particle is projected with a velocity v perpendicular to the fields, its path will be: A helix with increasing pitch A circle A helix with constant pitch A straight line A thin circular ring of radius R carries a charge Q and is rotating about its axis with a constant angular velocity . The magnetic dipole moment of the ring is: 1 2 Q R 2 Q R 2 2 Q R 2 1 4 Q R 2 A proton moves with a speed u in a magnetic field B in a circle of radius R . If the energy of the proton is doubled, the new radius will be: R 2 2R R/ 2 4R An electron moving with a velocity v enters a region where an electric field E and a magnetic field B are perpendicular to each other and also perpendicular to the velocity v . If the electron passes through the region undeflected, the velocity v is given by: v = E/B v = B/E v = E/B v = E 2/B A square loop of side L carries a current I . It is placed in a uniform magnetic field B = B 0 j such that the plane of the loop is the xz -plane. The torque on the loop is: Zero I B 0 L 2 k I B 0 L 2 i -I B 0 L 2 j A wire of length L carries a current I along the positive y -axis. It is placed in a magnetic field B = B 0(2 i + 3 k ) . The magnitude of the force on the wire is: I L B 0 13 5 I L B 0 I L B 0 5 I L B 0 The magnetic moment of a solenoid of length 0.5 m, radius 2 cm, having 500 turns and carrying a current of 2 A is: 1.26 Am 2 0.63 Am 2 2.52 Am 2 0.31 Am 2 A charged particle of mass m and charge q enters a uniform magnetic field B = B j with a velocity v = v x i + v y j . The radius of the resulting helical path is: mv x / (qB) mv y / (qB) m v x 2 + v y 2 / (qB) qB / (mv x) A wire of length L is bent into a semi-circle and carries a current I . It is placed in a uniform magnetic field B which is perpendicular to the plane of the loop. The magnetic force on the wire is: 2ILB / ILB ILB / Zero In a cyclotron, if the maximum radius is R and the magnetic field is B , the maximum kinetic energy of a deuteron (mass 2m , charge q ) compared to a proton (mass m , charge q ) is: Half Double Equal Four times A circular loop of radius r carries a current I . The loop is placed in a uniform magnetic field B such that the plane of the loop makes an angle of 30 with the magnetic field. The torque on the loop is: r 2 I B 3 2 r 2 I B / 2 r 2 I B Zero A point charge q is rotated in a circle of radius R with angular frequency . The magnetic dipole moment associated with this motion is: q R 2 / 2 q R 2 q 2 R / 2 q R / 2 The maximum kinetic energy of an accelerated particle in a cyclotron does NOT depend on: The frequency of the oscillator The radius of the dees The magnetic field strength The charge of the particle A particle of charge q is moving in a magnetic field B in a circle of radius R . If the kinetic energy of the particle is K , then R is proportional to: K K 1/ K K 2 The vertical component of Earth's magnetic field at a place is 0.2 G and the horizontal component is 0.4 G. The resultant magnetic field of Earth at that place is: 0.45 G 0.6 G 0.2 G 0.8 G A uniform rod of length L and charge Q is rotated with an angular velocity about an axis passing through one of its ends and perpendicular to its length. The magnetic moment of the rod is: 1 6 Q L 2 1 3 Q L 2 1 2 Q L 2 1 12 Q L 2 In a region, the magnetic field is B = 0.4 i T. A wire of length 20 cm carrying a current of 5 A is placed along the y -axis. The force acting on the wire is: 0.4 k N -0.4 k N 4 k N -4 k N A proton is moving in a circular path of radius R in a uniform magnetic field B . If the kinetic energy of the proton is doubled, the new radius will be: 2 R 2 R R/ 2 4 R A rectangular loop carrying a current I is situated near a long straight wire such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If a steady current I is established in the wire, the loop will: Move towards the wire Move away from the wire Rotate about an axis parallel to the wire Remain stationary Ionized hydrogen atoms and alpha-particles with same momenta enters perpendicular to a constant magnetic field B . The ratio of their radii of their paths r H : r will be: 2:1 1:2 4:1 1:4 A square loop of side L carrying current I is placed in the xy -plane. A uniform magnetic field B is applied along the z -axis. The torque experienced by the loop is: Zero IL 2 B I L B I L 2 B / 2 A current loop of area A and current I is placed in a magnetic field B . The work done in rotating the loop by 180 from its stable equilibrium position is: 2IAB IAB Zero -2IAB A charged particle moves in a magnetic field B with velocity v at an angle of 45 to the field. If the pitch of the resulting helix is P , what will be the pitch if the velocity is doubled and the angle is changed to 90 ? Zero 2P P/2 4P A very long straight wire carries a current I. At the instant when a charge +Q at point P has velocity V , as shown, the force on the charge is- Along ox Opposite to oy Along oy Opposite to ox In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular path 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 to 1/R 2 R 2 R 1/R