CHANAKYA SCIENCE ACADEMY

Std.: 11th & 12th (MHT CET) Physics Marks: 100

Date: 31-Oct-2023 Time: 1.25
Chapter:

Q.1 Attempt the following question - (Physics) 100

1 There is a long solenoid of radius 'R' having 'n' turns per unit length with current i flowing in it. A particle having
charge 'q' and mass 'm' is projected with speed 'v' in the perpendicular direction of axis from a Point on its axis
Find maximum value of 'v' so that it will not collide with the solenoid.
Rqμ 0in 2Rqμ 0in Rqμ 0in Rqμ 0in
(a) 2m
(b) m
(c) 3m
(d) 4m

Ans Option (a)

2 A current I ampere flows in a circular are of wire whose radius is R, which subtend an angle 3π/2 radian at its
centre. The magnetic induction B at the centre is

μ 0i μ 0i 2μ 0i 3μ 0i
(a) R
(b) 2R
(c) R
(d) 8R

Ans Option (d)

3 A positive charge enters a region of perpendicular electric and magnetic fields as shown in the figure,
travelling with speed V0 directed horizontally to the right. Initially the charge moves through the region shown
with no deflection and emerges through the hole in screen S2. If we now want the charge to hit below the hole
in the screen S2 we should

(a) Decrease its speed below V0 or increase the magnitude of E (b) Decrease its speed below V0, or decrease
the magnitude of E (c) Increase its speed above V0, or increase the magnitude of E (d) Increase its speed
above V0, or decrease the magnitude of E

Ans Option (c)

Ans Option (c)

4 A battery establishes a steady current around the circuit shown. A compass needle is placed successively at
points P,Q. and R, just above the wire (slightly out of the plane of the page). The relative deflection of the
needle, in descending order, is

(a) P, Q, R (b) Q, R, P (c) R, Q, P (d) Q, P, R

Ans Option (d)

5 An electron of mass m and charge q is travelling with a speed v along a circular path of radius r at right angles
to a uniform magnetic field B. If speed of the electron is doubled and of magnetic field is halved, then resulting
path would have a radius of
r r
(a) 4
(b) 2
(c) 2r (d) 4r

Ans Option (d)

6 An electron accelerated through potential difference V passes through a uniform transverse magnetic field
and experiences a force F. If the accelerating potential is increased to 2V, the electron in the same magnetic
field will experience a force
F
(a) 2
(b) 3F (c) F (d) √2F

Ans Option (d)

7 The current is flowing in south direction along a power line. The direction of magnetic field above the power
line (neglecting earth's field) is
(a) South (b) East (c) North (d) West

Ans Option (d)

8 A proton enters a magnetic field with velocity parallel to the magnetic field. The path followed by the proton is
a-
(a) circle (b) parabola (c) helix (d) straight line

Ans Option (d)

Since the velocity of the charged particle is parallel to the magnetic field, hence magnetic force on it is zero.

9 A straight wire carrying a current i1, runs along the axis of a circular current i2. Then the force of interaction
between the two current carrying conductors is

μ 0 2i 1i 2 2i 1i 2
(a) ∞ (b) Zero (c) 4π r
(d) r

Ans Option (b)

10 Given below are two statements:
Statement I: Electromagnetic waves are not deflected by electric and magnetic field.
Statement II: The amplitude of electric field and the magnetic field in electromagnetic waves are related to

√
μ0
each other E 0 = ε0
B0

In the light of the above statements, choose the correct answer from the options given below:
(a) Both Statement I and Statement II are false (b) Statement I is false but statement II is true (c) Both
Statement I and Statement II are true (d) Statement I is true but statement II is false

Ans Option (d)

11 A proton and an electron both moving with the same velocity v enter into a region of magnetic field directed
perpendicular to the velocity of the particles. They will now move in circular orbits such that
(a) Their time periods will be same (b) The time period for proton will be higher (c) The time period for
electron will be higher (d) Their orbital radii will be same

Ans Option (b)

12 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) qb B/m (b) q(b-a) B/m (c) qaB/m (d) q(b+a) B/2m

Ans Option (b)

13 ⇀
A particle of mass M and charge Q moving with velocity v describes a circular path of radius R when
subjected to a uniform transverse magnetic field of induction B. The work done by the field when the particle
completes one full circle is

(a) 2πBQvR (b)

( )
mv 2
R
2πR (c) Zero (d) 2πBQR

Ans Option (c)

Work done by the field is zero
W = F.d cos 90° = 0

14 A proton (mass m and charge +e) and an α- particle (mass 4m and charge +2e) are projected with the same
kinetic energy at right angles to the uniform magnetic field. Which one of the following statements will be
true?
(a) The α-particle will be bent in a circular path with a small radius that for the proton (b) The radius of the
path of the α-particle will be greater than that of the proton (c) The α-particle and the proton will be bent in a
circular path with the same radius (d) The α-particle and the proton will go through the field in a straight line

Ans Option (d)

15 A particle of charge -16 x 10-18 coulomb moving with velocity 10 ms-1 along the x-axis enters a region where a
magnetic field of induction B is along the y-axis and an electric field of magnitude 10 V/m is along the
negative z-axis. If the charged particle continues moving along the x-axis, the magnitude of B is
 (a) 105 Wb/m2 (b) 1016 Wb/m2 (c) 10-3 Wb/m2 (d) 103 Wb/m2

Ans Option (d)

16 A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per
minute at a place where dip angle is 30° and 15 oscillations per minute at a place where dip angle is 60o. The
ratio of the total earth's magnetic filed at the two places is-
(a) 3√3 : 8 (b) 16 : 9√3 (c) 4 : 9 (d) 2√3 : 9

Ans Option (b)

17 If the strength of the magnetic field produced 10cm away from a infinitely long straight conductor is 10-
5Weber / m2, the value the current flowing in the conductor will be

(a) 5 ampere (b) 10 ampere (c) 500 ampere (d) 1000 ampere

Ans Option (a)

18 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:

√ √
B B v v
(a) v
(b) v
(c) B
(d) B

Ans Option (c)

19 ⇀
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-
(a) T (b) 4T (c) 3T (d) 2T

Ans Option (a)

20 → →
The magnetic field dB due to a small current element d l at a distance →
r and element carrying current i is,

( ) ( ) ( ) ( )
→ → → →
→ → → →
→ μ0 dl × r → μ0 dl × r → μ0 dl × r → μ0 dl × r
(a) dB = i (b) dB = i2 (c) dB = i2 (d) dB = i
4π r 4π r 4π r2 4π r3

Ans Option (d)

21 A charged particle enters a magnetic field H with its initial velocity making an angle of 45°with H. The path of
the particle will be
(a) A straight line (b) A circle (c) An ellipse (d) A helix

Ans Option (d)

The component of velocity perpendicular to H will make the motion circular while that parallel to H will make it
move along a straight line. The two together will make the motion helical.

22 The dimension of the magnetic field intensity B is

(a) MLT-2A-1 (b) MT-2A-1 (c) ML2TA-2 (d) M2LT-2A-1

Ans Option (b)

23 Components of magnetic induction in Cartesian coordinates B are (0, 0, b), b>0. From the origin an electron
flies out with velocity components as (ux, uy, 0), where ux > 0, uy >0. Center of the circle, on which the electron
moves, is in the region:
(a) x>0, y>0 (b) x <0, y >0 (c) x <0, y<0 (d) x > 0, y<0

Ans Option (b)

24 The direction of magnetic lines of forces close to a straight conductor carrying current will be
(a) Along the length of the conductor (b) Radially outward (c) Circular in a plane perpendicular to the
conductor (d) Helical

Ans Option (c)

25 A proton, an electron, and a helium nucleus, have the same energy. They are in circular orbits in a plane due to
magnetic field perpendicular to the plane. Let rp. re and rHe be their respective radii, then,
(a) re > rp >rHe (b) re < rp < rHe (c) re < rp = rHe (d) re > rp = rHe

Ans Option (c)

26 A proton and an alpha particle having same momentum enter a magnetic field at right angles to it. If r1 and r2
be their radii. respectively then value of r1/r2 is
(a) 1 (b) 2 (c) 1/2 (d) 1/4

Ans Option (b)

27
( )
Two long parallel straight conductors carry current i 1 , and i 2 i 1 > i 2 . When the currents are in the same
direction,the magnetic field at a point midway between the wires is 20μT.If the direction of i 2 is reversed, the
field becomes 50μT. The ratio of the currents i 1 / i 2is:
(a) 5 / 2 (b) 7 / 3 (c) 4 / 3 (d) 5 / 3

Ans Option (b)

28 A particle having the same charge as of electron moves in a circular path of radius 0.5 cm under the influence
of a magnetic field of 0.5 T. If an electric field of 100 V/m makes it to move in a straight path, then the mass of
the particle is (Given charge of electron = 1.6 x 10-19 C)

(a) 2.0 x 10-24 kg (b) 1.6 x 10-19 kg (c) 1.6 x 10-27 kg (d) 9.1 x 10-31 kg

Ans Option (a)

29 A proton and an α-particle enter a uniform magnetic field perpendicularly with the same speed. If proton takes
25 µs to make 5 revolutions, then the periodic time for the α-particle would be
(a) 50 µs (b) 25 µs (c) 10 µs (d) 5 µs

Ans Option (c)

30 A current flows in a conductor from east to west. The direction of the magnetic field at a point above the
conductor is towards:
(a) east (b) west (c) north (d) south

Ans Option (c)

theory based question hence no detailing

31 For the magnetic field to be maximum due to a small element of current carrying conductor at a point, the
angle between the element and the line joining the element to the given point must be
(a) 0o (b) 90o (c) 180o (d) 45o

Ans Option (b)

32 A circular loop of radius r is carrying current I A. The ratio of magnetic field at the center of circular loop and at
a distance r from the the loop on its axis is:
(a) 1 : 3√2 (b) 2√2 : 1 (c) 3√2 : 2 (d) 1 : √2

Ans Option (b)

33 Two parallel conducting wires of equal length are placed distance d apart carry current I1 and I2 respectively in
opposite directions. The resultant magnetic field at the midpoint of the distance between both the wires is

(
μ0 I1 - I2 ) μ0 ( I1 + I2 ) μ0 ( I1 + I2 ) μ0 ( I1 - I2 )
(a) 2πd
(b) 2πd
(c) πd
(d) πd

Ans Option (c)

34 A current of 1 ampere is passed through a straight wire of length 2.0 metre. The magnetic field at a point in air
at a distance of 3 metre from either end of wire and lying on the axis of will be
μ0 μ0 μ0
(a) 2π
(b) 4π
(c) 8π
(d) Zero

Ans Option (d)

The magnetic field at any point on the axis of wire is Zero.

35 Two magnetic dipoles X and Y are placed at a separation with their axes perpendicular to each other. The
dipole moment of Y is twice that of X. A particle of charge q is passing through their midpoint P, at angle θ =
45° with the horizontal line, as shown in figure. What would be the magnitude of force on the particle at that
instant? (d is much larger than the dimensions of the dipole)

(a) √2
() () ()
μ0
4π
M

()
d
2
3
× qv (b)
μ0
4π
2M

()
d
2
3
× qv (c)
μ0
4π
M

()
d
2
3
× qv (d) 0

Ans Option (d)

36 A current carrying circular coil of radius R has a point P situated on its axis at a distance x from its centre O of

the coil. The magnetic induction at point Pis () 1

8
th
value of x is

R R 2
(a) (b) √3R (c) (d) R
2√ 3 √3 √3
Ans Option (b)

37 A long straight wire carrying a current of 30 A is placed in an external uniform magnetic field of induction
4x10-4 magnetic field is acting parallel to the direction of current. The magnitude of the resultant magnetic
induction in tesla at point 2.0 cm away from the wire is -
(a) 1 x 10-4 (b) 3 × 10-4 (c) 5 × 10-4 (d) 6 × 10-4

Ans Option (c)

38 A proton enters a magnetic field of flux density 1.5 weber/ m2 with a velocity of 2×107m/sec at an angle of 30°
with the field. The force on the proton will be
(a) 2.4 ×10-12 N (b) 0.24 × 10-12 N (c) 24 × 10-12 N (d) 0.024 × 10-12 N

Ans Option (c)

39 Two long straight wires P and Q carrying equal current 10 A were kept parallel to each other at 5 cm distance.
The magnitude of magnetic force experienced by 10 cm length of wire P is f. If the distance between wires is
halved and the currents on them are doubled, force F on 10 cm length of wire P will be:
f f
(a) 10 f (b) 8 f (c) 8
(d) 10

Ans Option (b)

40 An electron is travelling in east direction and a magnetic field is applied in upward direction, then electron will
deflect towards-
(a) south (b) north (c) west (d) east

Ans Option (b)

Theory based

41 A long thin hollow metallic cylinder of radius R has a current I ampere. The magnetic induction B away from
 the axis at a distance r from the axis varies as shown in

(a) (b) (c) (d)

Ans Option (a)

42 An electron is allowed to move with constant velocity along the axis of current carrying straight solenoid.
1. The electron will experience magnetic force along the axis of the solenoid.
2. The electron will not experience magnetic force.
3. The electron will continue to move along the axis of the solenoid.
4. The electron will be accelerated along the axis of the solenoid.
5. The electron will follow parabolic path-inside the solenoid.
Choose the correct answer from the codes given below:
(a) 2 and 3 only (b) 2 and 5 only (c) 2, 3 and 4 only (d) 1 and 4 only

Ans Option (a)

43 A charged particle moves through a magnetic field perpendicular to its direction. Then
(a) both momentum and kinetic energy of the particle are changed (b) its momentum changes but its kinetic
energy remains constant (c) its kinetic energy changes but momentum remains constant (d) both
momentum and kinetic energy of the particle remains constant

Ans Option (b)

Magnetic force is perpendicular to the direction of motion of the particle.
Therefore no external work is done and the kinetic energy remains constant. The particle undergoes uniform
circular motion, however due to change in direction of motion velocity is not constant. So the momentum is
not constant, during uniform circular motion. Therefore, option (B) is correct.

44 Magnetic field induction at the centre O of a square loop of side a carrying current I as shown in figure.

μ 0I μ 0I μ 0I
(a) (b) 2√2 (c) Zero (d)
πa πa 2πa
Ans Option (c)

45 A charge + Q is moving upwards vertically. It enters a magnetic field directed to the north. The force on the
charge will be towards
(a) North (b) South (c) East (d) West

Ans Option (d)

Use Fleming's right hand rule.

46 An electron moves with speed 2×105 m/s along the positive X - direction in the presence of a magnetic
induction B = î + 4 ĵ - 3k̂ (in Tesla).The magnitude of the force experienced by the electron in Newton's is
(charge on the electron =1.6 ×10-19C)
(a) 1.18 x 10-13 (b) 1.28 x 10-13 (c) 1.6 x 10-13 (d) 1.72 x 10-13

Ans Option (c)

47 A charged particle moves along circular path in a uniform magnetic field in a cyclotron. The kinetic energy of
the charged particle increases to 4 times its initial value. What will be the ratio of new radius to the original
radius of circular path of the charged particle:
(a) 1 : 1 (b) 1 : 2 (c) 2 : 1 (d) 1 : 4

Ans Option (c)

48 An electric charge moving with uniform velocity has

(a) only magnetic field around it (b) neither electric field nor magnetic field around it (c) only electric field
around it (d) both electric and magnetic field around it

Ans Option (d)

49 Two long straight wires are set parallel to each other. Each carries a current i in the same direction and the
separation between them is 2r. The intensity of the magnetic field midway between them is
 (a) µ0i/r (b) 4µ0i/r (c) Zero (d) µ0i/4r

Ans Option (c)

50 The magnetic induction at any point due to a long straight wire carrying a current
(a) Proportional to the distance from the wire (b) Inversely proportional to the distance from wire (c) Inversely
proportional to the square of the distance from the wire (d) Does not depend on distance

Ans Option (b)

51 An electron (mass = 9.0 × 10-31 kg and charge = 1.6 × 10-19 coulomb) is moving in a circular orbit in a
magnetic field of 1.0 × 10-4 weber/m2. Its period of revolution is -
(a) 3.5 × 10-7 second (b) 7.0 × 10-7 second (c) 1.05 x 10-6 second (d) 2.1 × 10-6 second

Ans Option (a)

52 A charge moves in a circular path perpendicular to a magnetic field. The time period of the revolution is
independent of

(a) strength of charge. (b) magnetic field. (c) mass of the charge. (d) velocity of the charge.

Ans Option (d)

The time period of a charged particle undergoing circular motion under uniform perpendicular magnetic field
2πm
is given by T = qB
So, it is independent of velocity.

53 Two long parallel wires are at a distance of 1 m. Both of them carry one ampere of current. The force of
attraction per unit length between the two wires is -
(a) 2 × 10-7 N/m
(b) 2 × 10-8 N/m
(c) 5 × 10-8 N/m
(d) 10-7 N/m

Ans Option (a)

54 A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular
→
to magnetic field B. The kinetic energy of the proton that describes a circular orbit of radius 0.5 metre in the
→
same plane with the same B is
(a) 25 keV (b) 50 keV (c) 200 keV (d) 100 keV

Ans Option (d)

55 An electron is travelling horizontally towards east. A magnetic field in vertically downward direction exerts a
force on the electron along
(a) East (b) West (c) North (d) South

Ans Option (d)

Fleming's left hand rule is used to determine the direction of force.

56 What is cyclotron frequency of on electron with an energy of 100 eV in the earth's magnetic field of 1x10-4
Wb/m2 if its velocity is perpendicular to magnetic field?
(a) 0.7 MHz (b) 2.1 MHz (c) 1.4 MHz (d) 2.8 MHz

Ans Option (d)

57 ⇀ ⇀
A charged particle moves with velocity v in a uniform magnetic field B . The magnetic force experienced by
the particle is
⇀ ⇀ ⇀ ⇀
(a) Always zero (b) Never zero (c) Zero, if B and v are perpendicular (d) Zero, if B and v are parallel

Ans Option (d)

58 The relation between electric filed E and magnetic field induction B in an electromagnetic wave-

√
μ0 B B
(a) E = B (b) E = (c) E = Bc (d) E =
ε0 c c2

Ans Option (b)

59 A 2 MeV proton is moving perpendicular to a uniform field of 2.5 tesla. The force on the proton is
(a) 2.5×10-10 N (b) 7.6×10-11 N (c) 2.5×10-11 N (d) 7.6×10-12 N

Ans Option (d)

60 Two particles X and Y having equal charges after being accelerated through same potential difference enter a
region of uniform magnetic field and describe a circular paths of radii r1 and r2 respectively. The ratio of the
mass of X to that of Y is

√ [] []
r1 r1 r2 2 r1 2
(a) r2
(b) r2
(c) r1
(d) r2

Ans Option (a)

61 Two ions having masses in the ratio 1 : 1 and charges 1 : 2 are projected into uniform magnetic field
perpendicular to the field with speeds in the ratio 2: 3. The ratio of the radii of circular paths along which the
two particles move is
(a) 4 : 3 (b) 2 : 3 (c) 3 : 1 (d) 1: 4

Ans Option (a)

62 Two charged particles, having same kinetic energy, are allowed to pass through a uniform magnetic field
perpendicular to the direction of motion. If the ratio of radii of their circular path is 6 : 5 and their respective
masses ratio is 9 : 4. Then, the ratio of their charges will be:
(a) 8 : 5 (b) 5 : 4 (c) 5 : 3 (d) 8 : 7

Ans Option (b)

63 When a charged particle moving with velocity v enters a region containing a perpendicular magnetic field, it
moves along a semi-circular path of radius 'r' as shown in the figure. Consider the following two statements:
(I) The radius 'r' of the semicircle is proportional to the initial speed v
(II)The time required for the particle to transverse the semicircle is independent of v.
Then.

(a) I is true, but II is incorrect (b) I is incorrect while II is true (c) I is true, II is also true and the two statements
are independent (d) I is true, II is also true and II is the cause of I.

Ans Option (d)

64 The given figure shows a set-up for accelerating protons from rest, through a potential (fixed) by the battery,
and then through a velocity selector. The E and B fields are carefully adjusted so that the accelerated protons
go straight through the slit after exiting the selector. You want to modify this so that electrons instead of
protons are used. You reverse the leads on the accelerating battery. What do you need to do to the potential
difference between the plates that create the electric field in the selector?

(a) Nothing (b) Reduce its magnitude (c) Increase its magnitude (d) Reverse the polarity, and reduce its
magnitude

Ans Option (c)

65 A charged particle with charge q is moving in a uniform magnetic field. If this particle makes any angle (other
than 180°) with the magnetic field, then its path will be-
(a) circular (b) straight line (c) helical (d) parabolic

Ans Option (c)

Component of velocity perpendicular to the magnetic field moves this charge particle in circular path, whereas
component of velocity in the direction of magnetic field moves this charge particle in the direction of field.
Hence path of this charge particle is helical.

66 Figure shows a square loop ABCD with edge length a. The resistance of the wire ABC is r and that of ADC is 2r.
The value of magnetic field at the centre of the loop assuming uniform wire is

√2μ 0i √2μ 0i
⊗ (c) √ ⊗
2μ 0i √2μ 0i
(a) ⊝ (b) ⊝ (d)
3πa 3πa πa πa

Ans Option (b)

67 A coaxial cable having radius "a" of inner wire and inner and outer radii "b" and "c" respectively of the outer
shell carries equal and opposite currents of magnitude i on the inner and outer conductors as shown. What is
the magnitude of the magnetic induction at point P of the cable at a distance r (b<r<c) from the axis?

(a) Zero (b)

μ 0ir
2πa 2
(c)
μ 0i
2πr
(d)
μ 0i
2πr ( )
c2 - r2
c2 - b2

Ans Option (d)

68 A proton, projected perpendicularly into a magnetic field with a certain velocity, follows a circular path. An
electron is then projected into the same region with the same initial velocity as the proton. If the electron is to
follow the exact same circular path as the proton, should the direction of the magnetic field be kept the same
or reversed, and should the magnitude of the magnetic field be increased or decreased?
(a) Keep the same field direction and increase its magnitude (b) Keep the same field direction and decrease
its magnitude (c) Reverse the field direction and increase its magnitude (d) Reverse the field direction and
decrease its magnitude

Ans Option (d)

69 A proton and an alpha particle are separately projected in a region where a uniform magnetic field exists. Their
initial velocities are perpendicular to direction of magnetic field. If both the particles move around magnetic

field in circles of equal radii, the ratio of momentum of proton to alpha particles
()
PP
Pα
is

1 1
(a) 1 (b) 2
(c) 2 (d) 4

Ans Option (b)

70 A free point charge q and mass m is at rest at the origin as shown in the figure. A constant electric field

( )
E o î + E o ĵ and constant magnetic field B 0 - k̂ is present in whole region. When this charge reaches at
position (2, 2,0), its speed will be:

√ √ √
8qE 0 4qE 0 qE 0

√
2qB
(a) m
(b) e m
(c) Bm
(d) m

Ans Option (a)

71 A long straight wire in the horizontal plane curries a current of 75 A in North of South direction, magnitude and
direction of field B at a point 3m East of the wire is
(a) 4×10-6 T vertical up (b) 5x10-6 T vertical down (c) 5x10-6 T vertical up (d) 4x10-6 T vertical down

Ans Option (b)

72 A one-metre-long wire is lying at right angles to the magnetic field. A force of 1 kg wt. is acting on it in a
magnetic field 0.98 Tesla. The current flowing in it will be
(a) 100 A (b) 10 A (c) 1 A (d) Zero

Ans Option (b)

73 A proton and an alpha particle enter a uniform magnetic field with the same velocity. The period of rotation of
the alpha particle will be
(a) Four times that of proton (b) Two times that of proton (c) Three times that of proton (d) The same as
that of proton

Ans Option (b)

74 Two straight parallel wires, both carrying 10 amperes in the same direction attract each other with a force of
1×10-3N. If both currents are doubled, the force of attraction will be
(a) 1×10-3N (b) 2×10-3N (c) 4×10-3N (d) 0.25×10-3N

Ans Option (c)

75 A cyclotron is used to accelerate protons. If the operating magnetic field is 1.0 T and the radius of the
cyclotron 'Dees' is 60 cm, the kinetic energy of the accelerated protons in MeV will be:
[use mp = 1.6 × 10-27 kg, e = 1.6 × 10-19 C]
(a) 12 (b) 18 (c) 16 (d) 32

Ans Option (b)

76 Two circular coils 1 and 2 are made from the same wire but the radius of the first coil is twice that of the
second coil. What is the ratio potential difference applied across them, so that the magnetic field at their
centres is same?
(a) 2:3 (b) 6:4 (c) 3:2 (d) 4:1

Ans Option (d)

77 3 A of current is flowing in a linear conductor having a length of 40cm. The conductor is placed in a magnetic
field of strength 500gauss and makes an angle of 30°with the direction of the field. It experiences a force of
magnitude

(a) 3 × 10 4N (b) 3 × 10 2N (c) 3 × 10 - 2N (d) 3 × 10 - 4N

Ans Option (c)

78 ⇀
At t = 0, a charge q is at the origin and moving in the y- direction with velocity v = v ĵ . The charge moves in
a magnetic field that is for y> 0 out of page and given by B 1 ẑ and for y < 0 into the page and given - B 2 ẑ. The
charge's subsequent trajectory is shown in the sketch. From this information, we can deduce that
 (a) q > 0 and|B1 | < |B2 | (b) q < 0 and |B1 | < |B2 | (c) q > 0 and |B1 | > |B2 | (d)
q < 0 and |B 1 | > |B 2 |

Ans Option (a)

79 The magnetic field at the centre of a circular coil of radius ors carrying current I is B1. The field at the centre of
another coil of radius 2r carrying same current I is B2. The ratio B1/B2 is
(a) 1 / 2 (b) 1 (c) 2 (d) 4

Ans Option (c)

80 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 k direction. The particle will genetrate in the region in this region in the x -direction
up to a distance d equal to
mv 2mv
(a) Zero (b) qB
(c) qB
(d) Infinity

Ans Option (b)

( ) (
81 ⇀ ⇀ ⇀ ⇀ ^ ⇀ ⇀
In the product F = q νxB = q ν x B î + B ĵ + Bk)For q = 1 and v = 2 î + 4 ĵ + 6k̂ F = 4 î - 20 ĵ + 12k̂

⇀
What will be the complete expression for B ?
(a) - 8 î - 8 ĵ - 6k̂ (b) - 6 î - 6 ĵ - 8k̂ (c) 8 î + 8 ĵ - 6k̂ (d) 6 î + 6 ĵ - 8k̂
Ans Option (b)

82 A current carrying long solenoid is placed on the ground with its axis vertical. A proton is falling along the axis
of the solenoid with a velocity v. When the proton enters into the solenoid, it will
(a) Be deflected from its path (b) Be accelerated along the same path (c) Be decelerated along the same
path (d) Move along the same path with no change in velocity

Ans Option (d)

Direction of motion of proton is same as that of direction of magnetic field.

83 When a battery is connected to the two ends of a diagonal of a square conductor frame of side 'a', the
magnitude of magnetic field at the center will be (uo permeability of free space)
μ0 √2μ 0 μ0
(a) (b) πa
(c) πa
(d) Zero
√2πa
Ans Option (d)

84 A particle is moving with velocity v = î - 3 ĵ and it produce an electric field at a point given by E = 2k̂. It will
produce magnetic field at that point equal to (all quantities are in SI units)
ˆ ˆ ˆ ˆ
- 6i - 2j 6i + 2j
(a) (b) (c) zero (d) cannot be determined from the given data
c2 c2

Ans Option (a)

85 A charged particle moves in a uniform magnetic field. The velocity of the particle at some instant makes an
acute angle with the magnetic field. The path of the particle will be
(a) A straight line (b) A circle (c) A helix with uniform pitch (d) A helix with non-uniform pitch

Ans Option (c)

When particle enters at angle other than 0° or 90° or 180°, path followed is helix. Pitch is uniform because
there is no any force in the direction of field.

86 At the centre of a straight solenoid the magnetic inductors is B. If the length is reduced to half but to keep the
number of turns same, these are wound in two layers, then the magnetic induction at the centre will be:
 (a) B / 2 (b) B (c) 2B (d) 4B

Ans Option (c)

87 A beam of electrons at rest is accelerated by a potential V. This beam experiences a force F in a uniform
magnetic field. The accelerating field is increased to V' and the force experienced by the electron in the same
V
field is '2F'. The ratio V'
(a) 2 : 1 (b) 1 : 2 (c) 1 : 4 (d) 1 : 1

Ans Option (c)

88 Two thin long parallel wires separated by a distance b are carrying a current i amp each. The magnitude of the
force per unit length exerted by one wire on the other is

μ 0i 2 μ 0i 2 μ 0i μ 0i
(a) 2 (b) (c) (d)
b 2πb 2πb 2πb 2

Ans Option (b)

89 An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of
105 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.

(a) 4 x 10 - 20 N (b) 8π x 10 - 20 N (c) 4π x 10 - 20 N (d) 8 x 10 - 20 N

Ans Option (d)

90 A vertical wire kept in Z-X plane carries a current from Q to P. The magnetic field due to current will have the
direction at origin O along

(a) OX (b) OX' (c) OY (d) OY'

Ans Option (d)

Use right hand palm rule, or Maxwell's cork screw rule.

91 When a magnetic field is applied in a direction perpendicular to the direction of cathode rays, then
(a) Energy decreases (b) Energy increases (c) Momentum increases (d) Magnitude of momentum and
energy remain unchanged

Ans Option (d)

92 The figure shows a particle (carrying charge +q) at the origin. A uniform magnetic field is directed into the
plane of the paper. The particle can be projected only in the plane of paper and along positive or negative x or
y axis. The particle moves with constant speed and has to hit a target located in the third quadrant. There are
two directions of projections, which can make it possible, these are

(a) +x and +y (b) +x and -y (c) -x and +y (d) -x and -y

Ans Option (c)

The charge will move in anticlockwise direction & the target should lie on the circumference of the circle
described by the change

93 The magnetic field at the centre of a current carrying circular coil an area 'A' is 'B'. The magnetic moment of
the coils is
[μ0 = permeability of free space.]
2BA 3 / 2 BA 2 μ 0π 1 / 2 BA 3 / 2
(a) (b) (c) (d)
μ 0π 1 / 2 μ 0π BA 3 / 2 μ 0π

Ans Option (a)

94 A charged particle is moving in a uniform magnetic field in a circular path. Radius of circular path is R. When
energy of particle is doubled, then new radius will be
(a) R√2 (b) R√3 (c) 2R (d) 3R

Ans Option (a)

95 A particle with charge q, moving with a momentum p, enters a uniform magnetic field normally. The magnetic
P
field has magnitude B and is confined to a region of width d, where d < Bq
. The particle is deflected by an
angle θ in crossing the field

Bqd P Bp pd
(a) sinθ = P
(b) sinθ = Bqd
(c) sinθ = qd
(d) sinθ = Bq

Ans Option (a)

96 If a proton, deuteron and α-particle on being accelerated by the same potential difference enter perpendicular
to the field, then the ratio of their kinetic energies is
(a) 1 : 2 : 2 (b) 2 : 2 : 1 (c) 1 : 2 : 1 (d) 1 : 1 : 2

Ans Option (d)

97 A proton accelerated by a potential difference 500 kV moves though a transverse magnetic field of 0.51 T as
shown in figure. The angle θ through which the proton deviates from the initial direction of its motion is

(a) 15° (b) 30° (c) 45° (d) 60°

Ans Option (b)

98 A charged particle of mass m and charge q travels on a circular path of radius r that is perpendicular to a
magnetic field B. The time taken by the particle to complete one revolution is :
2πmq 2πq 2B 2πqB 2πm
(a) B
(b) m
(c) m
(d) qB

Ans Option (d)

Theory based question hence no detailing

99 A particle of mass 0.6 g and having charge of 25 nC is moving horizontally with a uniform velocity 1.2 x 104
ms-1 in a uniform magnetic field, then the value of the minimum magnetic induction is
(g = 10ms-2) -
(a) Zero (b) 10 T (c) 20 T (d) 200 T

Ans Option (c)

100 An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 x 10-2 T. If
the value of e/m is 1.76 × 1011 C/kg, the frequency of revolution of the electron is
 (a) 6.28 MHz (b) 1 GHz (c) 100 MHz (d) 62.8 MHz

Ans Option (b)