Practice Test


1) The arms of magnetometer in the tan B position (Broad -side on ) are placed along :


2) Points A and B are situated along the extended axis of a 2 cm long bar magnet at a distance x and 2x cm respectively from the pole nearer to the points. The ratio of the fields at A and B will be :


3) If a bar magnet is placed with its north pole pointing towards north of earth, the neutral points are located :


4) The magnetic fields at a given distance from a short bar magnetic in longitudinal and transverse positions are in the ratio :


5) The line on surface of earth joining the points where H has same value is :


6) Two identical thin bar magnets each of length l and pole strength m are placed at right angles to each other with north pole of one touching south pole of other, the magnetic moment of the system is :


7) A magnet is placed vertically on a paper. Then the neutral point obtained on the paper is :


8) A steel wire of length l has a magnetic moment M. It is then bent into a semi-circular arc. The new magnetic moment is :


9) The arms of magnetometer in the end-on ( tan A) position are placed along :


10) Time period of a freely suspended magnet does not depend upon :


11) A magnetic needle suspended horizontally by unspun silk thread oscillates in the horizontal plane because of the restoring force originating mainly from :


12) A very thin steel needle with magnetic moment M and length l is cut into two equal pieces. If the time period of vibration in earth's field before cutting the needle is T, the time period of each half after cutting it is :


13) Two bar magnets when suspended with their norths along the magnetic meridian one above the other give a time period of 12s. When weaker of the two is reversed the period increases by 4s. Ratio of their moments is :


14) A dip needle in a plane perpendicular to the magnetic meridian will remain :


15) Susceptibility is positive but smaller for :


16) A magnet is vibrated horizontally in a plane perpendicular to the magnetic meridian, its frequency of vibration is :


17) The time period of horizontally suspended magnetic needle at the magnetic pole of earth is :


18) A magnetic needle is kept in a non-uniform magnetic field. It experiences :


19) Permeability of a diamagnetic is :


20) For paramagnetics :


21) A vibration magnetometer consists of two identical bar magnets placed one over the other such that they are mutually perpendicular and bisect each other. The time period of combination is 4s. If one of the magnets is removed, find the period of other ?


22) Isoclinic are the lines joining the places of :


23) Isogonic lines represents the lines of :


24) Agonic lines are :


25) Aclinic lines are of :


26) Which of the following substances has negative permeability and very large value of susceptibility ?


27) Which of the following properties has low value for ferrites ?


28) A magnet of pole strength m is divided into four equal parts so that the length as well as the breath of each part is half of the original magnet. Then the pole strength of each is :


29) A magnet of pole strength m is divided into four equal parts so that the length as well as the breath of each part is half of the original magnet. Then the dipole of each is :


30) Imaginary lines joining points of equal declination are called :


31) A magnet oscillates in earth's field with a time period T. If its mass is quadrupled, then its new time period will be :


32) A bar magnet with poles 25.0 cm apart and of pole strength 14.4 Am rests with its center on a frictionless point. It is held in equilibrium at 60 degrees to a uniform magnetic field of induction 0.25 T by applying a force F at right angle to the axes, 12 cm from its pivot. The magnitude of the force is :


33) A circular coil of radius 5.0 cm having 30 turns, lies in a horizontal plane. In carries a current of 5 A in clockwise sense when viewed from above. The magnetic moment of the coil is :


34) The value of Bohr-magneton is


35) The magnetic permeability of vacuum in C.G.S. system is :


36) To shield an instrument from the external magnetic field, it is placed inside a cabin made from :


37) The magnetic compass is not useful for navigation near the magnetic poles, since there :


38) A vibration magnetometer is placed at the south pole, then the time period will be :


39) A ferromagnetic material is heated above its curie temperature. Which one is a correct statement ?


40) A compass needle when placed at a geomagnetic pole stays along :


41) When a ferromagnetic material is taken through a hysteresis cycle, the magnetic susceptibility cannot be :


42) Electromagnets are made of soft iron because soft iron has :


43) Permanent magnets are made of steel because steel has :


44) A magnet is placed on a paper in a horizontal for locating neutral points. A dip circle is placed at the neutral point will horizontal at the :


45) The isodynamic lines are loci of equal :


46) A hydrogen atom is paramagnetic. A hydrogen molecule is :


47) Ferromagnetic owe their properties to :


48) The Hysteresis cycle for the material of a transformer is :


49) The Hysteresis cycle for the material of permanent magnet is :


50) Liquid and gases never show :


51) A magnetic north pole is :


52) A magnetic south pole is :


53) An isolated magnetic pole is :


54) A steel wire of length l has a magnetic moment M. It is then bent in L-shape at its mid point. The new magnetic moment is :


55) A person is facing magnetic north. An electron in front of him flies horizontally towards the north and deflects towards east. He is in/at :


56) A magnetic field is measured by :


57) A ferromagnetic material goes through hysteresis loop, the magnetic susceptibility


58) Which of the following graphs may best represent the current deflection relation in a tangent galvanometer ?


59) A magnet 20 cm long with its poles concentrated at its ends is placed vertically with its North pole on the table. At a point due 20 cm south ( magnetic ) of the pole a neutral point is located. IF horizontal component of the earth's field is H = 0.3 gauss, then the pole strength of the magnet is nearly :


60) A bar magnet suspended by a horse's hair lies in the magnetic meridian where there is no twist in the hair, on turning the upper end of the hair through 150 degree, the magnet is deflected through 30 degree from the meridian. Then, the angle through which the upper end of the hair has to be twisted to deflect the magnet through 90 degree from the meridian is :


61) A direct current I flows in a long straight conductor whose cross-section has a form of a thin half ring of radius R. The same current flows in opposite direction along a thin conductor placed on the axis of first conductor, then the magnetic interaction force between the conductors to a unit of their length is :


62) A vibration magnetometer consists of two identical bar magnets placed one above the other such that they are mutually perpendicular and bisect each other. The time period of oscillation in a horizontal magnetic field is 4s. If one of the magnets is taken away, then time period of oscillation of the other magnet in the same field is :


63) A magnet weights 75 g and its magnetic moment is 300 c.g.s units. The density of the material of the magnet is 7.9 g/c.c. The intensity of magnetisation is (in c.g.s units ) :


64) A thin rectangular magnet suspended freely has a period of oscillation of 4s. What will be the period of oscillation, if the magnet is broken into two halves ( each having half the original length ) one of the piece is made to oscillate in the same field ?


65) An iron bar of length 10 cm and diameter 2 cm is placed in a magnetic field of intensity 10 oersted with its length parallel to the direction of the field. The magnetic moment produced in the bar if permeability of its material is 629 is :


66) A metal wire of mass m slides without friction on two rails spaced at a distance d apart. The track lies in a vertical uniform field of induction B. A constant current I flows along one rail, across the wire and black down the other rail. The speed of the wire as function of time assuming it to be at rest initially :


67) A long solenoid of length 0.4 m and having 500 turns of wire carries a current of 3 A. A thin coil having 10 turns of wire and radius of 0.01m carries a current of 0.4 A. Calculate the torque required to hold the coil in the middle of the solenoid with its axis perpendicular to the axis of the solenoid :


68) An irregular closed loop carrying a current has shape that the entire loop cannot lie in a single plane. If this loop is placed in a uniform magnetic field, the force acting on the loop :


69) A coil having N turns is wound tightly in the form a spiral with inner and outer radii a and respectively. When a current I passes through the coil, the magnetic field at the center is :


70) Two north poles of pole strengths 0.4 Am and 6.4 Am are separated by 10 cm. The distance of the neutral points from 0.4 A m is :


71) A magnet of magnetic moment M oscillating freely in earth's horizontal field makes n oscillations per minute. If the magnetic moment is quadrupled and the earth's field is doubled, the number of oscillations made per minute would be :


72) The distances of two points on the axis of a magnet from its center are 10 cm and 20 cm respectively. The ratio of magnetic field at these points is 125 : 1. The length of the magnet is :


73) If a bar magnet of magnetic moment of 80 units be cut into two halves of equal lengths, the magnetic moment of the each half will be :


74) A circular coil of diameter 0.07 m has 24 turns of wire which carry current of 0.75 A. The magnetic moment of the coil is :


75) The time period of oscillation of a magnet in a vibration magnetometer is 1.5 second. The time period of oscillation of another magnet similar in size, shape and mass but having one-fourth magnetic moment than that of the first magnet oscillating at same place will be :


76) In two separate experiments, the neutral points due to two small magnets are a distance of r and 2r in broad side on position. The ratio of their magnetic moments will be :


77) The magnetic field at a point x on the axis of a small bar magnet is equal to the field at a point y on the equator of the same magnet. The ratio of the distances of x and y from the center of the magnet is :


78) If the ratio of earth's magnetic filed is 2 : 3, then the ratio of time periods of a magnet will be :


79) Points A and B are situated perpendicular to the axis of a 2 cm long bar magnet at large distances x and 3x from its center on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to :


80) The length of magnet is large as compared to a width and breadth. The time period of its oscillation in a vibration magnetometer is 2s. The magnet is cut along its length into three equal parts and these parts are then placed on each other with their like poles together. The time period of this combination will be :


81) The main use of studying the hysteresis curve for a given material is to estimate :


82) A bar magnet is held perpendicular to a uniform magnetic field. If the torque acting on the magnet is to be halved by rotating it, then angle by which it is to be rotated is :


83) Due to the earth's magnetic field, charged cosmic ray particles :


84) A moving charge will produce :


85) The magnetic susceptibility does not depend upon the temperature in :


86) A tangent galvanometer is used to measure :


87) The plane of the coil of a tangent galvanometer is vertical and perpendicular to the magnetic meridian. When a current is passed through the coil of the galvanometer, the magnetic needle deflects by :


88) Which of the following is a paramagnetic group :


89) In a deflection magnetometer, the external magnet should be replaced :


90) Curie temperature of iron is the temperature below which it is :


91) The period of oscillations of magnet is 2s. When it is remagnetised so that the pole strength is 4 times, its period will be :


92) The magnetic field of earth is due to :


93) A diamagnetic substance is placed in a magnetic field of a bar magnet. Then it is :


94) A diamagnetic material in a magnetic field moves :


95) According to Curie's law, the magnetic susceptibility of a substance, at an absolute temperature T, is proportional to :


96) A frog can be leviated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as :


97) The magnetic field lines due to a bar magnet are correctly shown in :


98) The magnetic resonance imaging (MRI) is based on the phenomenon of :


99) Liquid oxygen remains suspended between two poles of a magnet because it is :


100) At which place earth's magnetic field becomes horizontal ?


101) The pole strength of a bar magnet is 48 ampere-meter and the distance between its pole is 25 cm. The amount of the couple by which it can be placed at an angle 30 degrees with the uniform intensity of flux density 0.15 newton / ampere-meter will be:


102) Above curie temp :


103) Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature then it will show :


104) A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of 2 sec in earth's horizontal magnetic field of 24 microtesla. When a horizontal field of 18 microtesla is produced opposite to earth's field by placing a current carrying wire, the new time period of magnet will be :


105) There are four light-weight-rod samples A, B, C, D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted :
(i) A is freely repelled.
(ii) B is freely repelled.
(iii) C is strongly attracted.
(iv) D remains unaffected.
Which one of the following is true ?


106) The magnetic needle at magnetic pole becomes


107) A current I is flowing in a conductor of length l. When it is bent in the form of a loop then its magnetic moment will be


108) The resultant magnetic moment due to two current carrying concentric coils of radius r, mutually perpendicular to each other will be :


109) Magnetic fields do not interact with


110) Two bar magnets of the same mass, same length and breadth but having magnetic moment M and 2M are joined together pole for pole and suspended by a string. The time period of assembly in a magnetic field of strength H is 3 seconds. If now the polarity of one of the magnets is reversed and the combination is again made to oscillate in the same field, the time of oscillation is :


111) A bar magnet is oscillating in earth's magnetic field with a period T. What happens to its period and motion if its mass is quadrupled ?


112) The material of a permanent magnet has


113) A tangent galvanometer is most sensitive when the deflection is around


114) Force between two identical short bar magnets whose centers are r metre apart is 8.1 N, when their axes are long the same line. If separation is increased to 3r and the axis are rearranged perpendicularly, the force between them would become


115) The magnetic needle of an oscillation magnetomter makes 10 oscillations per minute under the action of earth's magnetic field alone. When a bar magnet is placed at some distance along the axis of the needle, it makes 14 oscillations per minute. If the bar magnet is turned so that its poles interchange their positions, then the new frequency of oscillations of the needle is


116) A dip needle vibrates in the vertical plane perpendicular to magnetic meridian. The time period of vibration is found to be 2 seconds. The same needle is then allowed to vibrate in the horizontal plane and time period is again found to be 2 seconds. Then the angle of dip is


117) A thin rectangular magnet suspended freely has a period of oscillation of 4s. If it is broken into two equal halves, the period of oscillation of each half will be :