Magnetic Effects of Current- 2 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.18) : There are 18 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A proton, a deutron and an a-particle are accelerated
through same potential difference and then they enter a
normal uniform magnetic field. The ratio of their kinetic
energies will be-
(a) 2 : 1 : 3 (b) 1 : 1 : 2 (c) 1 : 1 : 1 (d) 1 : 2 : 4
Q.2 A proton of energy 8eV is moving in a circular path in a
uniform magnetic field. The energy of an a-particle
moving in the same magnetic field and along the same path
will be-
(a) 4eV (b) 2eV
(c) 8eV (d) 6eV
Q.3 An electron is revolving in a circular path of radius
2×10
–10
 m with a speed of 3×10
6
 m/s. The magnetic field
at the centre of circular path will be-
(a) 1.2 T (b) 2.4 T (c)0 (d) 3.6 T
Q.4 An a particle travels at an angle of 30º to a magnetic field
0.8 T with a velocity of 10
5
 m/s. The magnitude of force
will be-
(a) 1.28 × 10
–14
 N (b) (1.28) Ö3 ×10
–4
 N
(c) 1.28 × 10
–4
 N (d) (12.8) Ö3 ×10
–4
 N
Q.5 A beam of protons is moving horizontally towards you. As
it approaches, it passes through a magnetic field directed
downward. The beam deflects-
(a) to your left side
(b) to your right side
(c) does not deflect
v
F ××
×
×
×
×
× × ×
×
×
× × × ×
(d) nothing can be said
Page 2


DIRECTIONS (Q.1-Q.18) : There are 18 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A proton, a deutron and an a-particle are accelerated
through same potential difference and then they enter a
normal uniform magnetic field. The ratio of their kinetic
energies will be-
(a) 2 : 1 : 3 (b) 1 : 1 : 2 (c) 1 : 1 : 1 (d) 1 : 2 : 4
Q.2 A proton of energy 8eV is moving in a circular path in a
uniform magnetic field. The energy of an a-particle
moving in the same magnetic field and along the same path
will be-
(a) 4eV (b) 2eV
(c) 8eV (d) 6eV
Q.3 An electron is revolving in a circular path of radius
2×10
–10
 m with a speed of 3×10
6
 m/s. The magnetic field
at the centre of circular path will be-
(a) 1.2 T (b) 2.4 T (c)0 (d) 3.6 T
Q.4 An a particle travels at an angle of 30º to a magnetic field
0.8 T with a velocity of 10
5
 m/s. The magnitude of force
will be-
(a) 1.28 × 10
–14
 N (b) (1.28) Ö3 ×10
–4
 N
(c) 1.28 × 10
–4
 N (d) (12.8) Ö3 ×10
–4
 N
Q.5 A beam of protons is moving horizontally towards you. As
it approaches, it passes through a magnetic field directed
downward. The beam deflects-
(a) to your left side
(b) to your right side
(c) does not deflect
v
F ××
×
×
×
×
× × ×
×
×
× × × ×
(d) nothing can be said
2
DPP/ P 40
Q.6 If a particle moves in a circular path in clockwise direction
after entering into a downward vertical magnetic field. The
charge on the particle is-
(a) positive (b) negative
(c) nothing can be said (d) neutral
Q.7 In the example above, after how much time, particle comes
to the starting point for the first time. (mass of particle =
m)
(a)
2
3
p m
qB
(b)
2 p m
qB
(c) Never
(d) It will leave the circular path before coming to the
starting point
Q.8 A current of 2.0 amp is flowing through a wire of length
50 cm. If this wire be placed at an angle of 60º with the
direction of a uniform magnetic field of 5.0 × 10
–4
 N/Am
the force on the wire will be-
(a) 4.33 × 10
–4
 N (b) 2.50 × 10
–4
 N
(c) 5.0 × 10
–4
 N (d) 2.33 × 10
–4
 N
Q.9 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) qa B/m (d) q(b + a) B/2m
Q.10 A particle with charge q, moving with a momentum p, enters
a uniform magnetic field normally . The magnetic field has
magnitude B and is confined to a region of width d, where
d < 
B
p
q
, The particle is deflected by an angle q in crossing
the field. Then
(a) sin q = 
Bqd
p
× × × ×
× × × ×
× × × ×
× × × ×
× × × ×
B
d
q
p
(b) sin q = 
B
p
qd
(c) sin q = 
Bp
qd
(d) sin q = 
B
pd
q
Q.11 An a particle is moving in a magnetic field of 
ˆˆ
(3i 2j) +
tesla with a velocity of 5×10
5 $
i m/s. The magnetic force
acting on the particle will be-
(a) 3.2 × 10
–13
 dyne (b) 3.2 × 10
13
 N
(c)0 (d) 3.2 × 10
–13
 N
Q.12 If an a-particle moving with velocity 'v' enters  perpendicular
to a magnetic field then the magnetic force acting on it will
be-
(a) evB (b) 2evB (c)0 (d) 4evB
Q.13 What is the net force on the square coil ?
10 cm
15 cm
1 A
2 cm
2 A
(a) 25 ´ 10
–7
 N towards wire
(b) 25 ´ 10
–7
 N away from wire
(c) 35 ´ 10
–7
 N towards wire
(d) 35 ´ 10
–7
 N away from wire
Q.14 A proton is to circulate the earth along the equator with a
speed of 1.0 × 10
7
 m/s. The minimum magnetic field which
should be created at the equator for this purpose.
(The mass of proton = 1.7 × 10
–27
 kg and radius of earth
= 6.37 × 10
6
 m.) will be (in Wb/m
2
)
(a) 1.6 × 10
–19
(b) 1.67 × 10
–8
(c) 1.0 × 10
–7
(d) 2 × 10
–7
Q.15 An a-particle is describing a circle of radius 0.45 m in a
field of magnetic induction  1.2 weber/m
2
. The potential
difference required to accelerate the particle, (The mass
of a-particle is 6.8 × 10
–27
 kg and its charge is 3.2 × 10
–
19
 coulomb.) will be —
(a) 6 × 10
6
 V (b) 2.3 × 10
–12
 V
(c) 7 × 10
6
 V (d) 3.2 × 10
–12
 V
Page 3


DIRECTIONS (Q.1-Q.18) : There are 18 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A proton, a deutron and an a-particle are accelerated
through same potential difference and then they enter a
normal uniform magnetic field. The ratio of their kinetic
energies will be-
(a) 2 : 1 : 3 (b) 1 : 1 : 2 (c) 1 : 1 : 1 (d) 1 : 2 : 4
Q.2 A proton of energy 8eV is moving in a circular path in a
uniform magnetic field. The energy of an a-particle
moving in the same magnetic field and along the same path
will be-
(a) 4eV (b) 2eV
(c) 8eV (d) 6eV
Q.3 An electron is revolving in a circular path of radius
2×10
–10
 m with a speed of 3×10
6
 m/s. The magnetic field
at the centre of circular path will be-
(a) 1.2 T (b) 2.4 T (c)0 (d) 3.6 T
Q.4 An a particle travels at an angle of 30º to a magnetic field
0.8 T with a velocity of 10
5
 m/s. The magnitude of force
will be-
(a) 1.28 × 10
–14
 N (b) (1.28) Ö3 ×10
–4
 N
(c) 1.28 × 10
–4
 N (d) (12.8) Ö3 ×10
–4
 N
Q.5 A beam of protons is moving horizontally towards you. As
it approaches, it passes through a magnetic field directed
downward. The beam deflects-
(a) to your left side
(b) to your right side
(c) does not deflect
v
F ××
×
×
×
×
× × ×
×
×
× × × ×
(d) nothing can be said
2
DPP/ P 40
Q.6 If a particle moves in a circular path in clockwise direction
after entering into a downward vertical magnetic field. The
charge on the particle is-
(a) positive (b) negative
(c) nothing can be said (d) neutral
Q.7 In the example above, after how much time, particle comes
to the starting point for the first time. (mass of particle =
m)
(a)
2
3
p m
qB
(b)
2 p m
qB
(c) Never
(d) It will leave the circular path before coming to the
starting point
Q.8 A current of 2.0 amp is flowing through a wire of length
50 cm. If this wire be placed at an angle of 60º with the
direction of a uniform magnetic field of 5.0 × 10
–4
 N/Am
the force on the wire will be-
(a) 4.33 × 10
–4
 N (b) 2.50 × 10
–4
 N
(c) 5.0 × 10
–4
 N (d) 2.33 × 10
–4
 N
Q.9 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) qa B/m (d) q(b + a) B/2m
Q.10 A particle with charge q, moving with a momentum p, enters
a uniform magnetic field normally . The magnetic field has
magnitude B and is confined to a region of width d, where
d < 
B
p
q
, The particle is deflected by an angle q in crossing
the field. Then
(a) sin q = 
Bqd
p
× × × ×
× × × ×
× × × ×
× × × ×
× × × ×
B
d
q
p
(b) sin q = 
B
p
qd
(c) sin q = 
Bp
qd
(d) sin q = 
B
pd
q
Q.11 An a particle is moving in a magnetic field of 
ˆˆ
(3i 2j) +
tesla with a velocity of 5×10
5 $
i m/s. The magnetic force
acting on the particle will be-
(a) 3.2 × 10
–13
 dyne (b) 3.2 × 10
13
 N
(c)0 (d) 3.2 × 10
–13
 N
Q.12 If an a-particle moving with velocity 'v' enters  perpendicular
to a magnetic field then the magnetic force acting on it will
be-
(a) evB (b) 2evB (c)0 (d) 4evB
Q.13 What is the net force on the square coil ?
10 cm
15 cm
1 A
2 cm
2 A
(a) 25 ´ 10
–7
 N towards wire
(b) 25 ´ 10
–7
 N away from wire
(c) 35 ´ 10
–7
 N towards wire
(d) 35 ´ 10
–7
 N away from wire
Q.14 A proton is to circulate the earth along the equator with a
speed of 1.0 × 10
7
 m/s. The minimum magnetic field which
should be created at the equator for this purpose.
(The mass of proton = 1.7 × 10
–27
 kg and radius of earth
= 6.37 × 10
6
 m.) will be (in Wb/m
2
)
(a) 1.6 × 10
–19
(b) 1.67 × 10
–8
(c) 1.0 × 10
–7
(d) 2 × 10
–7
Q.15 An a-particle is describing a circle of radius 0.45 m in a
field of magnetic induction  1.2 weber/m
2
. The potential
difference required to accelerate the particle, (The mass
of a-particle is 6.8 × 10
–27
 kg and its charge is 3.2 × 10
–
19
 coulomb.) will be —
(a) 6 × 10
6
 V (b) 2.3 × 10
–12
 V
(c) 7 × 10
6
 V (d) 3.2 × 10
–12
 V
DPP/ P 40
3
Q.16 An electron beam passes through a magnitic field of
2 × 10
–3
 weber/m
2
 and an electric field of 1.0 × 10
4
 volt/
m both acting simultaneously. If the electric field is
removed, what will be the radius of the electron path ?
(a) 1.43 cm. (b) 0.43 cm (c) 2.43 cm.(d) 3.43 cm.
Q.17 A straight horizontal copper wire carries a current i = 30
A. The linear mass density of the wire is 45 g/m. What is
the magnitude of the magnetic field needed to balance its
weight?
(a) 147 G (b) 441 G (c) 14.7 G (d) 0 G
Q.18 A 1m long conducting wire is lying at right angles to the
magnetic field. A force of 1 kg. wt is acting on it in a
magnetic field of 0.98 tesla. The current flowing in it will
be-
(a) 100 A (b) 10 A (c) 1 A (d)0
DIRECTIONS (Q.19-Q.20) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.19 In the fig the two parallel wires PQ and ST are at 30 cm
apart. The currents flowing in the wires are according to
fig. The force acting over a length of 5m of the wires is-
P
Q
S
10A
T 15A
(1) 5 × 10
–4
 N (2) attraction
(3) 5 × 10
–8
 N (4) repulsion
Q.20 A beam of protons enters a uniform magnetic field of 0.3
tesla with a velocity of 4 × 10
5
 m/s at an angle of 60º to
the field.  Then,
(Mass of the proton = 1.7 × 10
–27
 kg.)
(1) the radius of the helical path is 1.226 × 10
–2
 m
(2) the pitch of the helix is 4.45 × 10
–2
 m
(3) the radius of the helical path is 1.226 × 10
–3
 m
(4) the pitch of the helix is 4.45 × 10
–4
 m
DIRECTIONS (Q.21-Q.23) : Read the passage given below
and answer the questions that follows :
A charge particles q enters in a magnetic field 
ˆˆ
B yi xj =+
r
 with
the velocity 
ˆˆ
v xi yj =+
r
. Neglect any force other than magnetic
force. Now answer the following question.
Q.21 When particle arrives at any point P (2, 2) then force acting
on it, will be –
(a) Zero (b) 4 2q (c) 8q (d) 2 2q
Q.22 Magnetic force F acting on charge is proportional to –
(a) F µ (x
2
 – y
2
)
(b) F µ (x
2
 + y
2
)
(c) F µ 
22
xy +
(d) F does not depend on x or y co-ordinate
Q.23 Which of the following is true for the direction of magnetic
force ?
(a) if x > y then force works along (–z) direction
(b) if x < y then force works along (+z) direction
(c) if x > y then force works along (+z) direction
(d) None of these
DIRECTIONS (Qs. 24-Q.26) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.24Statement -1 : If two long wires, hanging freely are
connected to a battery in series, they come closer to each
other.
Statement -2 : Force of repulsion acts between the two
wires carrying current.
Page 4


DIRECTIONS (Q.1-Q.18) : There are 18 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A proton, a deutron and an a-particle are accelerated
through same potential difference and then they enter a
normal uniform magnetic field. The ratio of their kinetic
energies will be-
(a) 2 : 1 : 3 (b) 1 : 1 : 2 (c) 1 : 1 : 1 (d) 1 : 2 : 4
Q.2 A proton of energy 8eV is moving in a circular path in a
uniform magnetic field. The energy of an a-particle
moving in the same magnetic field and along the same path
will be-
(a) 4eV (b) 2eV
(c) 8eV (d) 6eV
Q.3 An electron is revolving in a circular path of radius
2×10
–10
 m with a speed of 3×10
6
 m/s. The magnetic field
at the centre of circular path will be-
(a) 1.2 T (b) 2.4 T (c)0 (d) 3.6 T
Q.4 An a particle travels at an angle of 30º to a magnetic field
0.8 T with a velocity of 10
5
 m/s. The magnitude of force
will be-
(a) 1.28 × 10
–14
 N (b) (1.28) Ö3 ×10
–4
 N
(c) 1.28 × 10
–4
 N (d) (12.8) Ö3 ×10
–4
 N
Q.5 A beam of protons is moving horizontally towards you. As
it approaches, it passes through a magnetic field directed
downward. The beam deflects-
(a) to your left side
(b) to your right side
(c) does not deflect
v
F ××
×
×
×
×
× × ×
×
×
× × × ×
(d) nothing can be said
2
DPP/ P 40
Q.6 If a particle moves in a circular path in clockwise direction
after entering into a downward vertical magnetic field. The
charge on the particle is-
(a) positive (b) negative
(c) nothing can be said (d) neutral
Q.7 In the example above, after how much time, particle comes
to the starting point for the first time. (mass of particle =
m)
(a)
2
3
p m
qB
(b)
2 p m
qB
(c) Never
(d) It will leave the circular path before coming to the
starting point
Q.8 A current of 2.0 amp is flowing through a wire of length
50 cm. If this wire be placed at an angle of 60º with the
direction of a uniform magnetic field of 5.0 × 10
–4
 N/Am
the force on the wire will be-
(a) 4.33 × 10
–4
 N (b) 2.50 × 10
–4
 N
(c) 5.0 × 10
–4
 N (d) 2.33 × 10
–4
 N
Q.9 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) qa B/m (d) q(b + a) B/2m
Q.10 A particle with charge q, moving with a momentum p, enters
a uniform magnetic field normally . The magnetic field has
magnitude B and is confined to a region of width d, where
d < 
B
p
q
, The particle is deflected by an angle q in crossing
the field. Then
(a) sin q = 
Bqd
p
× × × ×
× × × ×
× × × ×
× × × ×
× × × ×
B
d
q
p
(b) sin q = 
B
p
qd
(c) sin q = 
Bp
qd
(d) sin q = 
B
pd
q
Q.11 An a particle is moving in a magnetic field of 
ˆˆ
(3i 2j) +
tesla with a velocity of 5×10
5 $
i m/s. The magnetic force
acting on the particle will be-
(a) 3.2 × 10
–13
 dyne (b) 3.2 × 10
13
 N
(c)0 (d) 3.2 × 10
–13
 N
Q.12 If an a-particle moving with velocity 'v' enters  perpendicular
to a magnetic field then the magnetic force acting on it will
be-
(a) evB (b) 2evB (c)0 (d) 4evB
Q.13 What is the net force on the square coil ?
10 cm
15 cm
1 A
2 cm
2 A
(a) 25 ´ 10
–7
 N towards wire
(b) 25 ´ 10
–7
 N away from wire
(c) 35 ´ 10
–7
 N towards wire
(d) 35 ´ 10
–7
 N away from wire
Q.14 A proton is to circulate the earth along the equator with a
speed of 1.0 × 10
7
 m/s. The minimum magnetic field which
should be created at the equator for this purpose.
(The mass of proton = 1.7 × 10
–27
 kg and radius of earth
= 6.37 × 10
6
 m.) will be (in Wb/m
2
)
(a) 1.6 × 10
–19
(b) 1.67 × 10
–8
(c) 1.0 × 10
–7
(d) 2 × 10
–7
Q.15 An a-particle is describing a circle of radius 0.45 m in a
field of magnetic induction  1.2 weber/m
2
. The potential
difference required to accelerate the particle, (The mass
of a-particle is 6.8 × 10
–27
 kg and its charge is 3.2 × 10
–
19
 coulomb.) will be —
(a) 6 × 10
6
 V (b) 2.3 × 10
–12
 V
(c) 7 × 10
6
 V (d) 3.2 × 10
–12
 V
DPP/ P 40
3
Q.16 An electron beam passes through a magnitic field of
2 × 10
–3
 weber/m
2
 and an electric field of 1.0 × 10
4
 volt/
m both acting simultaneously. If the electric field is
removed, what will be the radius of the electron path ?
(a) 1.43 cm. (b) 0.43 cm (c) 2.43 cm.(d) 3.43 cm.
Q.17 A straight horizontal copper wire carries a current i = 30
A. The linear mass density of the wire is 45 g/m. What is
the magnitude of the magnetic field needed to balance its
weight?
(a) 147 G (b) 441 G (c) 14.7 G (d) 0 G
Q.18 A 1m long conducting wire is lying at right angles to the
magnetic field. A force of 1 kg. wt is acting on it in a
magnetic field of 0.98 tesla. The current flowing in it will
be-
(a) 100 A (b) 10 A (c) 1 A (d)0
DIRECTIONS (Q.19-Q.20) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.19 In the fig the two parallel wires PQ and ST are at 30 cm
apart. The currents flowing in the wires are according to
fig. The force acting over a length of 5m of the wires is-
P
Q
S
10A
T 15A
(1) 5 × 10
–4
 N (2) attraction
(3) 5 × 10
–8
 N (4) repulsion
Q.20 A beam of protons enters a uniform magnetic field of 0.3
tesla with a velocity of 4 × 10
5
 m/s at an angle of 60º to
the field.  Then,
(Mass of the proton = 1.7 × 10
–27
 kg.)
(1) the radius of the helical path is 1.226 × 10
–2
 m
(2) the pitch of the helix is 4.45 × 10
–2
 m
(3) the radius of the helical path is 1.226 × 10
–3
 m
(4) the pitch of the helix is 4.45 × 10
–4
 m
DIRECTIONS (Q.21-Q.23) : Read the passage given below
and answer the questions that follows :
A charge particles q enters in a magnetic field 
ˆˆ
B yi xj =+
r
 with
the velocity 
ˆˆ
v xi yj =+
r
. Neglect any force other than magnetic
force. Now answer the following question.
Q.21 When particle arrives at any point P (2, 2) then force acting
on it, will be –
(a) Zero (b) 4 2q (c) 8q (d) 2 2q
Q.22 Magnetic force F acting on charge is proportional to –
(a) F µ (x
2
 – y
2
)
(b) F µ (x
2
 + y
2
)
(c) F µ 
22
xy +
(d) F does not depend on x or y co-ordinate
Q.23 Which of the following is true for the direction of magnetic
force ?
(a) if x > y then force works along (–z) direction
(b) if x < y then force works along (+z) direction
(c) if x > y then force works along (+z) direction
(d) None of these
DIRECTIONS (Qs. 24-Q.26) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.24Statement -1 : If two long wires, hanging freely are
connected to a battery in series, they come closer to each
other.
Statement -2 : Force of repulsion acts between the two
wires carrying current.
4
DPP/ P 40
Q.25 Statement - 1 : For a charged particle to pass through a
uniform electro-magnetic field without change in velocity ,
its velocity vector must be perpendicular to the magnetic
field.
Statement - 2 : Net Lorentz force on the particle is given
by 
[] F qE vB = +´
r rr
r
.
Q.26 Statement - 1 : If an electron is not deflected while passing
through a certain region of space, then only possibility is
that there is no magnetic region.
Statement - 2 : Magnetic force is directly proportional to
the magnetic field applied.