Magnetic Field Questions and Answers

A semicircular wire PQS of radius R is connected to a wire bent in the form of a sine curve to form a closed loop as shown in the figure If the loop carries a current i and is placed in a uniform magnetic field B then the total force acting on the sine curve is 1 2BiR downward 2 2BiR upward 3 BiR upward Zero X S X X X X X X X

3 Positive like charge of linear charge density is passed on the outer circumference of an annular disc having outer radius 2R Negative like charge of linear charge density 2 is passed on the inner circumference of the disc having inner radius R The disc is rotating with constant angular velocity w about an axis passing through the centre of mass wills and perpendicular to its plane If the net magnetic field at the centre of the disc is 0 then the ratio 1 is X Lo ni o exsh xxx x x x

A wire carrying current I lie on the axis of a conducting ring The direction of the induced current in the ring when I is decreasing at a steady rate is clockwise anticlockwise alternatively clock and anticlockwise no induced current flow in the ring

You run a current through a coil of wire which is close to a permanent magnet Wha device will this create a a generator Ob a resistor Oc a motor d an electromagnet

When the number of turns in a toroidal coil is doubled the value of magnetic flux density will become four times eight times half double

Two long thin parallel conductors of the shape shown in Fig 3 71 carry direct currents I and I The separation between the conductors is a the width of the right hand conductor is equal to b With both conductors lying in one plane find the magnetic interaction force between them reduced to a unit of their length 1 F 1 bl 12

Moving harges 9 A current of 5 amperes flows through a circular coil of 500 turns and of radius 5 cm Find the magnetic field i at the centre of the coil and ii at a point 12 cm away from the centre of the coil along its axis the magnetic

If I hold a magnet still inside a coil of wire what happens a Nothing Ob The coil gets a magnetic field c Electric current is produced nail of wire is pushed away from the magnet

A 9V battery is hooked up to a simple DC motor Which answer choice best describes the energy conversions in this process a Light energy is converted to mechanical kinetic energy Ob Mechanical kinetic energy is converted to electric energy c Electric energy is converted to light energy d Electric energy is converted to mechanical kinetic energy

Students in a physics class observe that when they hook up a coil of wire wrapped around a nail to a battery it is able to pick up paper clips off of their table Which of the following is true concerning the relationship between electric currents and magnetic fields a The electric current in the coil produces a magnetic field which attracts the paper clips O b The magnetic field of the paper clips causes electric current to flow through the nail Oc The magnetic field of the paper clips causes electric current to flow through the coil of wire into the battery O d The electric current in the coil creates an electric current in the paper clips attracting them to the nail

A student wants to investigate the relationship between magnetic fields and electric current The student has a wire a permanent bar magnet an ammeter measures current and a battery Which of the following procedures could be used to observe that magnetic fields produce electric current a Connect the wire to the magnet and the battery and use the ammeter to see if it produces current O b Connect the wire to the battery next to a magnet and use the ammeter to measure the magnetic field O c Make a coil with the wire and connect it to the battery Then see if the coil attracts or repels the magnet O d Make a coil with the wire and move the magnet inside Use the ammeter to see the current that is produced

The segment AB of wire carrying current I is placed perpendicular to a long straight wire carrying current I2 as shown in figure The magnitude of force experienced by the straight wire AB is MoI1I2 A 2 T B C MoI1I2 2 T 1n3 1n2 2 11 12 2r I 2a Ba 12

b Directly Electromagnet c Invercely cm 2 0 3 0 4 0 5 0 of the Magnetic Field UT 48 6 21 4 12 1 According to this data magnetic field strength and distance are a Not 7 8 proportional

9 The earth receives 1400 W m 2 of solar energy The distance between the earth and the sun is 1 5 10 11 m What is the rate of decrease of the mass of the sun 1 Point 2 2 10 9 kg s 1 4 10 9 kg s 1 4 10 9 kg s

A coil of self inductance L is placed in an external magnetic field no current flows in the coil The total magnetic flux linked with the coil is p The magnetic field energy stored in the coil is A Zero B 2 2L C L D 201 L Your Answer A Answer B

Du and a friend have a 0 65 m length of copper ire that has a diameter of 4 115 mm and a ooden rod that is 85 mm long and has a diameter 10 mm You re aiming to wind the wire around e rod about 40 times to form an inductor Part A What is the maximum inductance you can achieve with this device Neglect the incomplete wi and use the number of full windings in your calculation Use the cross section area of the woo as the area of each winding Express your answer with the appropriate units A

A coil of one loop is made by a wire of length L and there after a coil of two loops is made by same wire The ratio of magnetic field at the centre of coils respectively 1 1 4 2 1 1 3 1 8 4 4 1 Magnetic field at point O will be

A particle whose mass is twice the mass of proton and charge is four times the charge of proton is allowed through a uniform magnetic field of strength 1 7 mT and is perpendicular to the velocity of the particle Find the radius and time period of revolution of the particle if the velocity of the particle is 2 5x10 m s a 1 28 cm 56 10 s b 7 7 cm 1 9 10 s c 2 64 cm 24 10 s d 3 56 cm 13 106 s

Two wires with currents 2 A and 1 A are enclosed in a circular loop Another wire with current 3 A is situated outside the loop as shown The B dl around the loop is Kerala PET 2010 a Ho c 640 e Zero 2A 1A 3A igral sci b 340 d 240 0 d B the

A square frame made of wire with diameter d is placed near a long straight wire carrying current I When this current is turned off a momentum p is imparted to the frame What momentum would be imparted to the frame if the initial current is 31 and diameter of wire is 2d If your answer is np fill n in OMR sheet In

6 A square loop of side a carrying current i is placed in the xy plane as shown in the figure Find the flux of magnetic field for the region x 0 shaded region A Hola K Hola 3x C In 2 In 2 uo B D Mola in 2 2x Hola In 2 4t

Two solenoids each of radius 2 cm are placed coaxially with a gap of 1 cm between them Determine the magnetic field in Gauss at the centre of the gap if a current of 2 A flows through the two solenoids in series Assume that each solenoid contains 40 turns per cm 0 S 02 P 2 cm 0 L 1 cm S Z axis

6 An Insolated conductor initially free from charge is charged by repeated contacts with a plate which after each contact has a charge Q due to some mechanism If q is the charge on the conductor after the first operation prove that the maximum charge which can be given to the L conductor in this way is

Four long parallel wires pass through the corners of a square with side 0 900 m All four wires carry the same magnitude of current 79 0 A in the directions indicated R Find the magnitude of the magnetic field at point P the midpoint of the top side of the square

and the charged particle is moving along the positive x axis Fig 4 4 the magnetic field is parallel to the positive y axis which way would the Lorentz force be for a an electron negative charge b a proton positive charge Z XX xxxx xxx xx x y xxxxx XX XX xx xXxxxx xxxxxxxxx FIGURE 4 4 Xxxxxxxxxxxx xxxxxxxxxxx xxxxxxxxx xxxxxxxx XX x Solution The velocity v of particle is along the x axis while B the magnetic field is along the y axis so v x B is along the z axis screw rule or right hand thumb rule So a for electron it will be along axis b for a positive charge proton the force is along z axis

A cyclotron accelerates deutrons The radius of the dee is 0 8 m and the frequency of the cyclotron s oscillator s IMHZ a Find the number of times a deutron enters into the gap between the dees in one second

Consider the wire which is in a region of uniform magnetic field of magnitude B 2 3T carries a current of I 18A as shown in the figure below If 47cm a 45 and is making an angle of 0 22 degress determine the net force acting on the wire Express your answer in units of N using one decimal places y x 18 X l X X 0 X X X X X

A conducting ring of radius L 2m is placed on X Y plane having its centre at the origin as shown in the figure A uniform magnetic field 5T k exists in the space A conducting rod PQ of mass M and length 2L is placed along the diameter of the rail as shown Rod is free to rotate about z axis on the smothering A resistance R is connected to the centre O and periphery of the ring At t 0 the rod PQ is given an angular velocity 1 k rad sec Find the ratio of the numerical values of the charge flown through the resistor to the heat generated through the resistor during the time interval the rod keeps on rotating P R www Z O

The plane of the circular current carrying loop having radius 1 52 cm and mass 2 5 g is making an angle of 25 with the uniform magnetic field having a magnitude of 4 6 10 T The current passing through the loop is 3 4 A Calculate the magnitude of the angular acceleration of the circular loop nswer a 71 rad s b 18 rad s2 c 24 rad s d 18 rad s A

A long straight wire carries current I There is quarter ring of radius 3a present near it as shown Find force on the quarter ring Quarter ring is in the plane of paper and long wire is perpendicular to the plane of paper A H 11 112 TO B H 2 In 5 2 a C 3a H II In 2 5 3 D Holz I 2 In 2

A region of space has a uniform magnetic field Bk A particle having mass m and charge q enters into the region at the origin with a velocity vi vk a Write the velocity of the particle at time after it enters the field b Write the co ordinates of the particle as a function of time

When the pressure on a given mass of liquid is increased from 3 MPa to 3 5 MPa the density of the liquid increases from 500 kg m to 501 kg m the average value of bulk modulus of liquid over the given pressure range will be MPa

A conducting rod of mass m 0 3 kg and length 4m can slide without friction on two parallel conducting rails The conducting rails are connected via an inductance L 3mH This system is placed in a region containing uniform magnetic field B 1T pointing into the plane If the rod is given an initial velocity vo 2 m s it oscillates with an amplitude A cm Find the value of 2A lellele Vo O B

3 A line charge of linear density is paste on the rim of a wheel of mass M and radius R The wheel has light non conducting spokes and is free to rotate about a vertical axis A uniform magnetic field extends over a circular region centered at the centre of wheel given by B Bok for r a and B for r a 1 B MR Z What is angular velocity acquired by the wheel as the field is suddenly switched off A a B 2 MR 22 m p

A field of strength 5x10 ampere turns meter acts at right angles to the coil of 50 turns of area 102 m The coil is removed from the field in 0 1 second then the induced e m f in the coil 1 0 1 V 3 1 96V 2 0 2V

A straight 10 cm wire bent at its midpoint so as to form an angle of 90 carries a current of 15 A It lies in the xy plane in a region where the magnetic field is in the positive z direction and has a constant magnitude of 3 0 mT What is the magnitude of the magnetic force on this wire Select one Oa 6 4 mN Ob 3 2 mN O c 4 2 mN d 2 1 mN O

proton travels with a speed of 4 95 x 106 m s at an angle of 58 with the direction of a magnetic field of magnitude 0 170 T in the positive x directi a What is the magnitude of the magnetic force on the proton N b What is the proton s acceleration Give the magnitude m s

A straight wire carrying current i is turned into a circular loop If the magnitude of magnetic moment associated with it in M K S unit is M the length of wire will be 1 4 iM 2 3 4M 4 i VM

4 Spe The time period of a charge particle which is projected in a magnetic field B with velocity at an angle 0 with the direction of magnetic field is NCERT Pg 138 2 m 1 qB 2 m cose 24 2 m qB sine 2 m 4 qB tan0

5 4 Will be magnitude 5p inclined at tan will x axis The coercivity of a small bar magnet is 4 x 10 Am It is inserted inside a solenoid of 50 turns and length 1m to demagnetize it The amount of current to be passed through the solenoid will be 1 2 5 A 3 8A 4 10 A 2 5A

8 In a region of space a uniform magnetic field of induction B Bk is established A particle moving with velocity U in this region experiences a viscous drag f ku where k is a positive constant A particle of mass m and charge q is projected with velocity u ui in this region Find its displacement when it practically stops

42 A circular coil of radius 5 cm having a total of 10 turns is placed so that its plane coincides with the magnetic meridian plane i e the vertical plane in the north south direction It is rotated about its vertical diameter by 45 and a current of 2A is passed through it A magnetic needle placed at the centre of this coil points west to east The horizontal component of the earth s magnetic field is a 20 10 5T c 4x10 7T b 4x10 5T 4 d x10 5T TC

Example 6 11 Kamla peddles a stationary bicycle the pedals of the bicycle are attached to a 100 turn coil of area 0 10 m The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0 01 T perpendicular to the axis of rotation of the coil What is the maximum voltage generated in the coil 2 P 00 T Employing

3 Two identical particles having the same mass m and charges q and q separated by a distance d enter in a uniform magnetic field B directed perpendicular to paper inwards with speeds v and v2 as shown in figure The particles will not collide if Ignore electrostatic force X a d c d m Bq 2m Bq d V1 X X X X V X X X V V V V X X X X X X X B m b d v V Bq d V V

All questions are compulsory In case of internal choices attempt anyone 17 Two straight infinitely long wires are fixed in space so that the current in the left wire is 2A and directed out of the plane of the page and the current in the right wire is 3Aand directed into the plane of the page In which region s is are there a point on the x axis at which the magnetic field is equal to zero due to these currents carrying wires Justify your answer Region I 2A Region II 3A Region III Or A short bar magnet of magnetic moment 0 5 J T is placed with its axis at 30 to a uniform magnetic field 0 1T Calculate the magnitude of the torque experienced and the direction on which it acts

1 An electron and a proton are moving under the influence of mutual forces In calculating the change in the kinetic energy of the system during motion one ignores the magnetic force of one on another This is because a the two magnetic forces are equal and opposite so they produce no net effect b the magnetic forces do no work on each particle c the magnetic forces do equal and opposite but non zero work on each particle d the magnetic forces are necessarily negligible 6

ALLEN A square current carrying loop of side a produced magnetic field at its centre is B Find magnetic moment of this loop in terms of B various regular nolvaons shown below Find magnetic moment

A proton moves through a region containing a uniform electric field given by E 74 0 V m and a uniform magnetic field B 0 200 1 0 300j 0 400 k T Determine the acceleration of the proton when it has a velocity 170 1 m s m s2

4 65 A small coil of radius 0 002m is placed on the axis of a magnet of magnetic moment 105 J t and length 0 1m at a distance of 0 15m from the centre of the magnet The plane of the coil is perpendicular to the axis of the magnet Find the force on the coil when the current of 2 0 amp is passed through it Ans 4 396 10 N

rries current i ound to be 4 39 The value of horizontal component of earth s magnetic field at a place is 0 35 x 104 T If the angle of dip is 60 the value of vertical component of earth s magnetic field is about A 0 10 104T B 0 2 x 104T C 0 40 104T D 0 6 10 T