Practice Test


1) Current is passed through a straight wire. The magnetic field established around it has its lines of force:


2) There are two parallel wires attracting each other when same current is passed through them in the same direction, they are brought closer, the force of attraction shall :


3) A certain length of wire carrying current is bent in the form of a coil of one turn. The same wire is then bent to form two turns of smaller radius. the magnetic induction at its center for the same current is :


4) Two identical coils carrying same current have common center but have their planes at right angles to each other. If the field due to each is B, what is the resultant field ?


5) A straight conductor is split into identical semi-circular turns by tearing it into two parts from within. A current enters at one end and after passing through two parts leaves at the other. The field at the center of the loop of radius r is :


6) A straight wire carrying current and placed in the field experiences maximum force if :


7) Particles carrying positive charge travel from sky towards earth. On entering the earth's field they get deflected towards :


8) A uniform electric field and a uniform magnetic field are produced pointing in the same direction. An electron projected with a velocity pointing in the same direction will :


9) A wire with current directed towards east is placed in magnetic field directed north, the force on the wire is :


10) A magnetic needle is put in a non-uniform magnetic field it will experience :


11) If a proton is projected perpendicular to the field with velocity v and an electron is projected along the field, which of the following holds ?


12) A galvanometer having resistance of 20 ohm and capable of carrying a maximum current of 40 mA is to be converted into an ammeter of range 0-5 A, the galvanometer is to be converted into a voltmeter of range 5 volt, what is the resistance needed ?


13) A moving charge would produce :


14) Two circular loops of equal radii are placed, one vertically and other horizontally with a common center. The current flowing is clockwise in both and has same magnitude. The direction of magnitude field at the center:


15) Magnetic induction in a long straight wire is :


16) A wire of a given length is first bent in one loop and then in three loops. If the same current is passed in the both cases, the ratio of magnetic field induction at the centers will be :


17) A strong magnetic field is applied on a stationary electron, then :


18) The no. of turns and radius of cross-section of the coil are doubled. If the current remains the same, the magnetic field at the center of the coil is :


19) Two circular coil of wire carrying currents and of radii 20 cm and 40 cm are connected in parallel. The ratio of the magnetic fields at their centers is :


20) The magnetic field at the center of a square loops of side L carrying a current I is :


21) Magnetic induction due to long straight wire carrying current at a point on the wire itself is :


22) If a long hollow copper pipe carries a direct current, the magnetic field associated with current will be :


23) A current of 10 A is established in a long wire along the positive z-axis. The magnetic field at the point (1, 0, 0) meter is :


24) P is a point mid-way between two infinite thin wires carrying current as shown, the net field at the point P is :


25) Two long straight horizontal parallel wires, one above the other are separated by a distance 2a. If the wires carry equal currents in opposite direction, the magnitude of the field at a middle point between them is :


26) A circular loop of radius R carrying a current I is placed in a uniform magnetic field with its plane perpendicular to B.The force on the loop is :


27) A circular loop of radius R carrying a current I is placed in a uniform magnetic field with its plane perpendicular to B.The torque on the loop is :


28) Weber ampere per meter is equal to :


29) A moving coil voltmeter is generally used in the laboratory to measure the potential difference across a conductor of resistance r carrying current I. Voltmeter has resistance R and will measure the potential difference more correctly as :


30) Fig. shows two long conducting wires placed at right angles. then carry currents as indicated. Assumes that 1A current in a long wire produces magnetic field B at a distance d from the wire. Then strength and direction of the field at the point X marked in the Fig. will be :


31) No force is exerted by a magnetic field on


32) What is the magnetic field in the empty space enclosed by toroidal solenoid of radius R ?


33) Magnetic field due to a current carrying toroidal solenoid is independent of :


34) A very long solenoid has 800 turns per meter length of the solenoid. A current of 1.6 ampere flows through it. Then, magnetic induction at the end of the solenoid on its axis is :


35) A particle of charge q and mass m moving with a velocity v along the x-axis enters the region x > 0 with uniform magnetic field B along the z-direction. the particle will penetrate in this region in the x-direction upto a distance d equal to :


36) Two parallel beams of electrons moving in the same direction, produce a mutual force of :


37) A electron is shot into a liquid placed in a uniform magnetic field, in a plane perpendicular to the magnetic field. Then :


38) A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field :


39) Two ions have equal masses but one is singly ionized and the other is doubly ionized. They are projected from the same place in a uniform magnetic field with same velocity perpendicular to the field.


40) A charged particle is projected into a uniform magnetic field with velocity perpendicular to direction of the field. which of the following quantities of particle will not change ?


41) The magnetic induction at a point O, distance r from the corner of an infinitely long wire carrying current I and bent at right angle is :


42) Two particles each of mass m and charge q are attached to the two ends of a light rod of length 2R. The rod is rotated at the constant angular speed about a perpendicular axis passing through its center. The radio of the magnitude of the magnetic moment of the system and its angular momentum about the center of the rod is :


43) A long metal cylinder of radius r has a current I flowing through it. The magnetic induction B will vary with distance from the center as shown in :


44) A long hollow metal cylinder of radius R has a current I flowing through it. The magnetic induction B will vary with distance from the center as shown in :


45) A charge moves in a circle perpendicular to a magnetic field. The time period of revolution is independent of :


46) An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field of B at the center of the circle. The radius of the circle is proportional to :


47) Which of the following graphs correctly represents the variation of energy density u near the mid-point of a long current carrying conductor with magnetic field B ?


48) A charged particle is released from rest in a region of steady and uniform electric and magnetic field which are parallel to each other. The particle will move in a :


49) An electron is moving along positive x-axis. To get it moving on an anti-clockwise circular path in x-y plane, a magnetic field is applied :


50) A conductor of length 1 m carrying a current of 1 A is placed parallel to magnetic field 1 gauss. The magnetic force acting on the conductor is :


51) A current - carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend upon :


52) Two identical long solenoids carry the same constant current. When they are very far apart, the flux density at the center of each end of each solenoid is B. The solenoids are now arranged coaxially end to end with the current in each flowing in the same sense. The flux density on the axis in the region of contact is :


53) A current carrying straight wire is kept along the axis of a circular loop carrying a current. The straight wire :


54) Which of the following particles will experience maximum magnetic force ( magnetic ) when projected with the same velocity perpendicular to a magnetic field ?


55) A charged particle is situated in a region of space and it experiences a force only when it is in motion. It can be deduced that the region encloses :


56) An electric current I enters and leaves a uniform circular wire radius a through diametrically opposite points. A charged particle q moving along the axis of a circular wire passes through its center at speed v. The magnetic force acting on the particle when it passes through the center has a magnitude :


57) A proton beam is going from north to south and an electron beam is going from south to north. Neglecting the earth's magnetic field, the electron beam will be deflected :


58) The material used for the suspension wire of moving coil galvanometer is :


59) A rectangular coil of area A of N turns has a current I flowing in clockwise direction when looked at from above. The magnetic moment associated with it :


60) To measure total charge displaced through its terminals, we use :


61) A current is flowing north along a power line. The direction of magnetic field above it, neglecting the earth's field is :


62) Two long thin wires distant a apart exert a force F on one another when current through each wire is I. The distance between the wires is doubled and the current is decreased to I/3. The force they exert on another, now is :


63) The pole pieces of the magnetic field whose direction is perpendicular to the velocity of the electron. Then :


64) A current carrying small loop behaves like a small magnet. If A be its area and M its magnetic moment, the current in the loop will be :


65) A circular loop carrying a current is replaced by an equivalent magnetic dipole. A point on the axis of the loop is now on :


66) Two wires of equal length are placed perpendicular to the plane of paper at a distance of 5 cm from each other. If the currents flowing in first and second wires are 2A and 5A respectively in opposite directions, then the resultant magnetic field at mid-point of both the wires is :


67) A length L of wire carries a steady current I. It is bent first to form a circular plane coil of one turn. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the center caused by the same current is :


68) A current of 10 ampere is flowing in a wire of length 1.5 m. A force of 15 newton acts on it when it is placed in a uniform magnetic field of 12 tesla. The angle between the magnetic field and the direction of the current is :


69) An ionized gas contains both positive and negative ions. If it is subjected simultaneously to an electric field along the +x direction and a magnetic field along the +z direction, then :


70) Two long parallel wires are at a distance 2d apart. They carry steady equal currents flowing out of the plane of the paper, as shown in fig. The variation of the magnetic field B along the line XX' is given by :


71) Two long parallel wires at distance d apart carry currents of 1 A and 3 A in the same direction. The wire carrying 1 A current lies to the left of the other wire. The points at which their magnetic fields cancel are located at :


72) Cyclotron is used to accelerate :


73) A closely wound flat circular coil of 25 turns of wire has diameter of 10 cm and carries a current of 4 ampere. Determine the flux density at the center of coil.


74) A long vertical wire in which a current produces a neutral point with the earth's magnetic field at a distance of 5 cm from the wire. If the horizontal component of the earth's magnetic induction is 0.18 gauss, then the current in the wire is :


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


76) Neutrons enter a magnetic field B in different directions with the same speed v. Which of the following statements is true ?


77) The magnetic field of a certain length of wire for single turn coil at its center is B. Its value for two turns coil for the same wire is :


78) A charged particle moves in a circular path in a uniform magnetic field. The radius of circular path is R. When energy of particle is doubled, then new radius will be :


79) A particle of mass m and charge q moves with a constant velocity v along the positive x direction. It enters a region containing a uniform magnetic field B directed along the negative z direction, extending from x=a to x =b. The minimum value of v required so that the particle can just enter the region x > b is :


80) An electron is travelling along the x-direction. It is encounters a magnetic field in the y-direction. Its subsequent motion will be :


81) When a charged particle moves perpendicular to a magnetic field, then :


82) A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, then new value of the magnetic field is :


83) A wire of certain length carries a steady current. It is first bent to form a circular coil of one turn. The same wire is next bent to form a circular coil of three turns. The ratio of magnetic inductions at the center of the coil in the two cases is :


84) The magnetic field (B) due to straight conductor of uniform cross-section of radius (a) and carrying a steady current (I) is represented by :


85) Two parallel beams of positions moving in the same direction will :


86) A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from center of the coil, such that r > > R varies :


87) The magnetic moment of a current (I) carrying circular coil of radius (r) and number of turns (n) varies as :


88) The cyclotron frequency of an electron gyrating in a magnetic field of 1 T is :


89) A circular radius 'a' carries a current I. The magnetic induction at its center O due to the current is B. The distance from O of a point on the axis where the induction is B/8 is :


90) The straight of the magnetic field at a point r near a long straight current carrying wire is B. The field at a distance r/2 will be :


91) Electron of mass m and charge e is travelling with a speed v along the circular path of radius r at right angles of a uniform magnetic field B. If the speed of the electron is doubled and the magnetic field is halved the resulting path would have a radius :


92) A particle having charge 'q' enters a magnetic field perpendicular to it, then which of the following is true ?


93) A vertical straight conductor carries a current vertically upwards. A point P lies to the east of it at a small distance and another point Q lies to the west at the same distance. The magnetic field at P is :


94) Two circular coils 1 and 2 are made from the same wire but radius of 1st coil is twice that of 2nd coil. What potential difference in volts should be applied across them so that the magnetic field at their centers is same ?


95) A beam of electrons 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


96) 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 :


97) A plate of iron oscillates first in a region having a magnetic field and then in a region with no field :


98) A circular coil carrying a current is placed in a magnetic field. The torque on the coil will be one-half in maximum value, when the normal to the coil is :


99) Reluctance of the circuit is


100) In which of the situations given below will no force be experienced ?


101) A beam of proton is directed along the negative direction of X-axis in a magnetic field along the +ve direction of Y-axis in XY plane. It will get deflected along :


102) The moving galvanometer can be made more sensitive :


103) A current I flows along the length of an infinitely long straight thin walled pipe. then


104) An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy. Which of the following is true ?


105) In order to convert a milliametter of range 1.0 mA and resistance 1.0 ohm into a voltmeter of range 10V, a resistance of how many ohm should be connected with it and in what manner ?