Magnetic Field Questions and Answers

A circular coil of radius R and a current I which can rotate about a fixed axis passing through its diameter is initially placed such that its plane lies along magnetic field B Kinetic energy of loop when it rotates through an angle 90 is Assume that I remains constant A R2BI B TRBI 2 C 2 R BI D TR TR I

12 Figure 35 W10 shows a cross section of a large metal sheet carrying an electric current along its surface The current in a strip of width dl is Kdl where K is al constant Find the magnetic field at a point P at a distance x from the metal sheet P O O O O O O O O O O 25 W10 TxL 1 STUDE

remove slowest emitted photoelectrons iii What is the stopping potential iv What is the cut off Ans i 1 9875 eV ii zero iii 1 9875 V iv 2946 wavelength for aluminium 7 The most energetic photoelectrons emitted from a surface by 3500 photons bend in a 0 18 m circle by a magnetic field of 1 5 x 105 T Find the work function of the surface Ans 2 9 eV

TC A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole It CBSE AIPMT 2012 a will become rigid showing no movement b will stay in any position c will stay in North South direction only d will stay in East West direction only

80 A circular wire ABC and a straight conductor ADC are carrying current i and are kept in the magnetic field B then considering points A and C 1 Force as per ABC is more than ADC 2 Force as per ABC is less than ADC 3 Force as per ABC is equal to that as per ADC 4 Any of 1 or 2 or 3 12 bu B D A F Idla B sin

2 The number of turns per unit length of a long solenoid is 10 If its average radius is 5 cm and it carries a current of 10 A then the ratio of flux densities obtained at the centre and at the end on the axis will be 1 1 2 2 2 1 3 1 1

2 2 In the following graph the change of magnetic flux between t 0 to f 3 s is 1 10 weber 50 weber 21 Induced emf 10 V 2 t s 3 2 5 weber 4 20 weber

38 Magnetic fleld changing at the rate of 4T sec in a circular region of 5 cm radius The value of induced electric field at a point P which is 10 cm distance away from the centre O of region is 5 cm 1 0 05 V m 3 0 5 V m dt 10 cm 2 0 2 V m 4 2V m

A magnetic field B Boy a k is into the plane of paper in the z direction B and a are positive constants A square loop EFGH of side a mass m and resistance R in x y plane starts falling under the influence of gravity Note the directions of x and y axes in the figure Find a the induced current in the loop and indicate its direction b the total Lorentz force acting on the loop and indicate its direction c an expression for the speed of the loop v t and its terminal value Jed y E x G H de06 B0AH A KotaVEE A

The dipole moment of the given charge distribution is a c 4Rq TC 4Rq TU 2Rq TU 9 d 2Rq TT R 9

Magnetic field at P due to given structure is Ho 10 4T 2R Mo 5 0 3 4T 6R R 2 Mo 610 4t 5R Ho 2 0 4 R

23 A charged particle moves in a magnetic field 8 101 with initial velocity 5i 4j The path of the particle will be A straight line C helical Sol B circle D none

11 Electric field intensity at a point in between two parallel sheets with like charges of same surface charge densities o is a 280 b o b 80 c zero d 20 E

3 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 a qbB m c qaB m b q b a B m d q b a B 2m 37

33 There are two stationary fields of force F ayi and F axi byj where i and j are the unit vectors of the x and y axes and a and b ar constants Find out whether these fields are potential

A long wire carries a current of 90A from east to we direction Magnetic field due to current at a poi which is 1 5 m vertically below the wire 1 12 x 10 6 T towards north 2 6x10 6T towards south 3 12 x 10 6 T towards south 4 6 x 10 6 T towards north

A long straight wire of radius a carries a steady current I The current is uniformly distributed across its cross section The ratio of the magnetic field at a 4 is 1 1 1 2 7 16 1 3 inside and outside from the surface of wire 4 NCERT Pg 149 a 15 16 Uo 0

Twelve indentical capacitors each of capacitance C are connected as shown in figure 6C A The effective capacitance between P and T is 5 B The effective capacitance between P and U is 4C 3 12C C The effective capacitance between P and V is D All of the above statements are incorrect U Ans A B C

55 The magnetic field dB due to a small current element dl at a distance 7 and element carrying current i is a dB 02 di xr 4T i 4t b dB Ho i 4 c dB Ho r TT d dB 02 4t dl xr di x r di x 7 1996

30 Choose the correct statement 1 It is possible for a current loop to stay without rotating in a uniform magnetic field 2 If a uniform magnetic field exists in a cubical region and zero outside then it is not possible to project a charged particle from outside into the field so that it describes a complete circle in the field 3 A moving charged particle can be accelerate by a magnetic field 4 All of these

Q7 A wire loop with a 10 0 cm and b 15 0 cm and a long straight wire is arranged as shown in figure The current in the wire is changing according with a relation i 5 0t 10 0t where i is in amperes and t is in seconds K b b a Find the emf in the square loop at t 4 0 s b What is the direction of the induced current in the loop

A hollow non conducting sphere of radius R has a positive charge q uniformly distributed on its surface The sphere starts rotating with a constant angular velocity o about an axis passing through center of sphere as shown in the figure Then the net magnetic field at center of the sphere is A B C How 2 R How 6 R D Ho9 3 R Hoq 12TR O 9 R

Find The area enclosed by a circular coil of 2000 turns is 10 cm Its plane is kept perpendicular to a magnetic field of 0 3 Wb m2 and is rotated through 180 Calculate the magnitude of change in magnetic flux

A flat coil with radius 8 mm has fifty loops of wire on it It is placed in a magnetic field of 0 3 T so that the maximum flux goes through it Later it is rotated in 0 02 s to a position such that no flux goes through it Find the average emf induced between the terminals of the coil Two concentric pirou

target Find the force imparted by the beam on the target if the beam current is equal to I 1 An infinite uniform current carrying wire is kept along z axis carrrying current I in the direction of the positive z axis OABCDEFG represents a circle where all the points are equally spaced whose centre at point 4m 0 m and radius 4 m as shown in the figure If B d DEF unit then find the value of k YA E 00 4m 0 m D A Holo in S I A shus grinde OLD BIS A Stries Horlw tomoubnoo

and q masses m and m and having rad R and R respectively are rotating wit angular velocity o then the gyro magnetic rati of the system will be x 40 R q R q R 1 2 m R m R 9 92 3 2 m R m R2 x XX R XX i xxx q R q R 2 2 m m 4 None

A particle of specific charge q m is projected from the origin of coordinates with initial velocity ui vj Uniform electric and magnetic fields exist in the region along the y direction of magnitude E and B The particle will definitely return to the origin once if B u v 2 B TE is an integer D uB TE is an integer odi nwone A VB 2TE is an integer C VB TE in an integer peopubnoo gnol owT

A long cylindrical volume contains a uniformly distributed charge of density p Find the flux due to the electric field through the curved surface of the small cylinder whose axis is OP and whose radius is a Here O lies on the axis AB of the main cylinder containing the charge density p and its axis OP is perpendicular to AB and lies completely within the main cylinder A 60 X B

2 At a point A on the earth s surface the angle of dip 8 25 At a point B on the earth s surface the angle of dip 8 25 We can interpret that 1 A and B are both located in the northern hemisphere 2 A is located in the southern hemisphere and B is located in the northern hemisphere 3 A is located in the northern hemisphere and B is located in the southern hemisphere 4 A and B are both located in the southern hemisphera 45

y A conducting wire is bent in the form of a parabola y 2x carrying a current i 2A as shown in the figure The wire is placed in a uniform magnetic field B 4K The magnetic force on the wire is A 161 C 32i B 32i D 16i 2m 0 X

Magnetic dipole moment of Het hydrogen like atoms in the ground state will be g is Bohr magneton 1 zero 3 HB 2 HB 2 3 4 B

A straight wire of diameter of 0 5 mm carrying a current of 1A is replaced by another wire of 1mm diameter carrying the same current The strength of magnetic field far away is unchanged B quarter of its earlier value twice the earlier value half of the earlier value D A C

Ans 0 8 Nm A square coil of side 10 cm has 20 turns and carries a current of 12 A The coil is suspended vertically the normal to the plane of the coil makes an angle of 30 with the direction of a uniform horizontal magnetic field If the torque experienced by the coil equals 0 96 N m find the magnitude of the magnetic field C B S E 2010 S Ans 0 8 TI

particle of m and charge q enter with velocity v in region where magnetic field in only right of PQ line of magnitude B Find magnitude of change in velocity V 3 Opiul 2 2V 4 Fooso O 3 V 2 4 zero

The potential difference across a 10 H inductor as a function of time is shown in the figure At t 0 current is zero Then A The current in the inductor at t 6 sec is 3 amp B The current in the inductor at t 1 sec is 1 4 amp C The current in the inductor at t 4 sec is 5 2 amp D The variation of current versus time is parabola V Volts 10 V 0 10 2 6 sec

1 Magnetic flux is a scalar quantity 2 The unit for magnetic flux is Weber 3 Magnetic flux has direction 4 The magnitude of the magnetic flux value does not depend on the area The exact statement about magnetic flux

A charge moving with constant velocity produces 1 Only electric field 2 Only magnetic field 3 Both electric and magnetic field and also radiates 4 Both electric and magnetic field and does not radiates

A long straight wire carrying a current of 30 A is placed in an external uniform magnetic field of induction 4 x 104 T The magnetic field is acting parallel to the direction of current The magnitude of the resultant magnetic induction in tesla at a point 2 0 cm away from the wire is uo 4 x 10 7 H m hollis B 3 10 4 C 5 x 10 4 D 6 x 10 4 A 10 4 81

Two forces are applied to a 5 0 kg object and it accelerates at a rate of 2 0 m s2 in the positive y direction If one of the forces acts in the positive x direction with magnitude 12 0 N find the magnitude of the other force

A particle of charge q and mass m starts moving from origin under the action of an electric field E Ei and B Boi with velocity v v The time after which its speed becomes 2v is 1 2 3 4 2mvo qEo 2B 9 mvo 3 Boq mvo 3 mvo

11 Magnetic field at the centre O due to the give structure is 1 3 NE Mol 3 1 4R 2 T O Mol 3 1 R 2 O R M 3 1 2R Moll 4 AR 2 3 0

A circular flexible current loop of radius R carrying current is placed in an inward magnetic field B If we spin the loop clockwise with angular speed w then tension in string Assume the mass of the loop is m XX XXX 1 Is zero 2 Is more than IBR 3 Is less than iBR X XB X X X ad on rotation

3 A steady current is set up in a network composed of wires of equal resistance and length d as shown in Figure What is the magnetic field at the centre P B C a H Ho 21 4x d E P D G F c 0 Pamprayed Grank b Ho 31 4x 2d d Ho Onl 4n d

1 A coil in the shape of square is placed in a variable magnetic field which varies at the rate o dB dt as shown in figure The magnitude of em between points a and d along path abcd will be 1 2 L B L dB 2 dt dB dt 3 2L dt 4 31 2 dB dt O d C dB dt

An a particle is travelling at right angles to magnetic field with a speed of 6 105 m s strength of the magnetic field is 0 2 T Calculate i Force on the a particle ii Acceleration of the o particle

Two vectors A and B are such that A B C and I IBHCI Then the vectors A and B are 1 parallel 3 anti parallel 2 perpendicular 4 null vectors

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 1 Rotate about an axis parallel to the wire 2 Move away from the wire 3 Move towards the wire

Find the magnetic induction due to a straight conductor of length 16 cm carrying current of 5 A at a distance of 6 cm from the mid point of conductor

4 along the bisector of the 6 Magnetic field due to a small current carrying ring at some distance a on its axis is B from its center The magnetic field on the axis at a distance 4a from its center will be about 1 0 0156 B 3 0 25 B 2 4 0 5 B 0 125 B rrying

63 If pulled out with a uniform velocity from the uniform magnetic field as shown in figure then which graph of induced current versus time is possible 1 X X B X X X X A XV X X X t 2 B