Moving Charges and Magnetism Practice Questions - DPP for JEE

 Page 1


PART-I (Single Correct MCQs)
1. Two long parallel wires carry currents i
1
 andn i
2
 such that i
1
 > i
2
. When
the currents are in the same direction, the magnetic field at a point
midway between the wires is 6 × 10
–6
 T. If the direction of i
2
 is
reversed, the field becomes 3 × 10
–5
 T. The ratio of  is
(a)
(b) 2
(c)
(d)
2. A wire carrying current I has the shape as shown in adjoining figure.
Linear parts of the wire are very long and parallel to X-axis while
semicircular portion of radius R is lying in Y-Z plane. Magnetic field at
Page 2


PART-I (Single Correct MCQs)
1. Two long parallel wires carry currents i
1
 andn i
2
 such that i
1
 > i
2
. When
the currents are in the same direction, the magnetic field at a point
midway between the wires is 6 × 10
–6
 T. If the direction of i
2
 is
reversed, the field becomes 3 × 10
–5
 T. The ratio of  is
(a)
(b) 2
(c)
(d)
2. A wire carrying current I has the shape as shown in adjoining figure.
Linear parts of the wire are very long and parallel to X-axis while
semicircular portion of radius R is lying in Y-Z plane. Magnetic field at
point O is :
(a)
(b)
(c)
(d)
3. A closely wound solenoid of 2000 turns and area of cross-section 1.5 ×
10
–4
 m
2 
carries a current of 2.0 A. It suspended through its centre and
perpendicular to its length, allowing it to turn in a horizontal plane in a
uniform magnetic field 5 × 10
–2
 tesla making an angle of 30° with the
axis of the solenoid. The torque on the solenoid will be:
(a) 3 × 10
–2
 N-m
(b) 3 × 10
–3
 N-m
(c) 1.5 × 10
–3
 N-m
(d) 1.5 × 10
–2
 N-m
4. An alternating electric field, of frequency v, is applied across the dees
(radius = R) of a cyclotron that is being used to accelerate protons (mass
= m). The operating magnetic field (B) used in the cyclotron and the
kinetic energy (K) of the proton beam, produced by it, are given by :
(a) and K = 2mp
2
?
2
R
2
(b) and K = m
2
p?R
2
(c) and K = 2mp
2
?
2
R
2
(d) and K = m
2
p?R
2
5. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 ×
10
–4
 ampere gives a deflection of one per division. To convert this
galvanometer into a voltmeter having a range of 25 volts, it should be
connected with a resistance of
(a) 2450 ? in series
(b) 2500 ? in series.
Page 3


PART-I (Single Correct MCQs)
1. Two long parallel wires carry currents i
1
 andn i
2
 such that i
1
 > i
2
. When
the currents are in the same direction, the magnetic field at a point
midway between the wires is 6 × 10
–6
 T. If the direction of i
2
 is
reversed, the field becomes 3 × 10
–5
 T. The ratio of  is
(a)
(b) 2
(c)
(d)
2. A wire carrying current I has the shape as shown in adjoining figure.
Linear parts of the wire are very long and parallel to X-axis while
semicircular portion of radius R is lying in Y-Z plane. Magnetic field at
point O is :
(a)
(b)
(c)
(d)
3. A closely wound solenoid of 2000 turns and area of cross-section 1.5 ×
10
–4
 m
2 
carries a current of 2.0 A. It suspended through its centre and
perpendicular to its length, allowing it to turn in a horizontal plane in a
uniform magnetic field 5 × 10
–2
 tesla making an angle of 30° with the
axis of the solenoid. The torque on the solenoid will be:
(a) 3 × 10
–2
 N-m
(b) 3 × 10
–3
 N-m
(c) 1.5 × 10
–3
 N-m
(d) 1.5 × 10
–2
 N-m
4. An alternating electric field, of frequency v, is applied across the dees
(radius = R) of a cyclotron that is being used to accelerate protons (mass
= m). The operating magnetic field (B) used in the cyclotron and the
kinetic energy (K) of the proton beam, produced by it, are given by :
(a) and K = 2mp
2
?
2
R
2
(b) and K = m
2
p?R
2
(c) and K = 2mp
2
?
2
R
2
(d) and K = m
2
p?R
2
5. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 ×
10
–4
 ampere gives a deflection of one per division. To convert this
galvanometer into a voltmeter having a range of 25 volts, it should be
connected with a resistance of
(a) 2450 ? in series
(b) 2500 ? in series.
(c) 245 ? in series.
(d) 2550 ? in series.
6. In the adjoining figure, two very long, parallel wires A and B
carry currents of 10 ampere and 20 ampere respectively, and
are at a distance 20 cm apart. If a third wire C (length 15 cm)
having a current of 10 ampere is placed between them, then
how much force will act on C ? The direction of current in all
the three wires is same.
(a) 3 × 10
–5
 N (left)
(b) 3 × 10
–5
 N (right)
(c) 6 × 10
–5
 N (left)
(d) 6 × 10
–5
 N (right)
7. A 2 µC charge moving around a circle with a frequency of 6.25 × 10
12
Hz produces a magnetic field 6.28 tesla at the centre of the circle. The
radius of the circle is
(a) 2.25 m
(b) 0.25 m
(c) 13.0 m
(d) 1.25 m
8. A current loop ABCD is held fixed on the plane
of the paper as shown in the figure. The arcs BC
(radius = b) and DA (radius = a) of the loop are
joined by two straight wires AB and CD.  A
steady  current I is flowing in the loop. Angle
made by AB and CD at the origin O is 30°.
Another straight thin wire with steady current I
1
flowing out of the plane of the paper is kept at
the origin.
The magnitude of the magnetic field (B) due to the loop ABCD at the
origin (O) is :
(a)
(b)
Page 4


PART-I (Single Correct MCQs)
1. Two long parallel wires carry currents i
1
 andn i
2
 such that i
1
 > i
2
. When
the currents are in the same direction, the magnetic field at a point
midway between the wires is 6 × 10
–6
 T. If the direction of i
2
 is
reversed, the field becomes 3 × 10
–5
 T. The ratio of  is
(a)
(b) 2
(c)
(d)
2. A wire carrying current I has the shape as shown in adjoining figure.
Linear parts of the wire are very long and parallel to X-axis while
semicircular portion of radius R is lying in Y-Z plane. Magnetic field at
point O is :
(a)
(b)
(c)
(d)
3. A closely wound solenoid of 2000 turns and area of cross-section 1.5 ×
10
–4
 m
2 
carries a current of 2.0 A. It suspended through its centre and
perpendicular to its length, allowing it to turn in a horizontal plane in a
uniform magnetic field 5 × 10
–2
 tesla making an angle of 30° with the
axis of the solenoid. The torque on the solenoid will be:
(a) 3 × 10
–2
 N-m
(b) 3 × 10
–3
 N-m
(c) 1.5 × 10
–3
 N-m
(d) 1.5 × 10
–2
 N-m
4. An alternating electric field, of frequency v, is applied across the dees
(radius = R) of a cyclotron that is being used to accelerate protons (mass
= m). The operating magnetic field (B) used in the cyclotron and the
kinetic energy (K) of the proton beam, produced by it, are given by :
(a) and K = 2mp
2
?
2
R
2
(b) and K = m
2
p?R
2
(c) and K = 2mp
2
?
2
R
2
(d) and K = m
2
p?R
2
5. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 ×
10
–4
 ampere gives a deflection of one per division. To convert this
galvanometer into a voltmeter having a range of 25 volts, it should be
connected with a resistance of
(a) 2450 ? in series
(b) 2500 ? in series.
(c) 245 ? in series.
(d) 2550 ? in series.
6. In the adjoining figure, two very long, parallel wires A and B
carry currents of 10 ampere and 20 ampere respectively, and
are at a distance 20 cm apart. If a third wire C (length 15 cm)
having a current of 10 ampere is placed between them, then
how much force will act on C ? The direction of current in all
the three wires is same.
(a) 3 × 10
–5
 N (left)
(b) 3 × 10
–5
 N (right)
(c) 6 × 10
–5
 N (left)
(d) 6 × 10
–5
 N (right)
7. A 2 µC charge moving around a circle with a frequency of 6.25 × 10
12
Hz produces a magnetic field 6.28 tesla at the centre of the circle. The
radius of the circle is
(a) 2.25 m
(b) 0.25 m
(c) 13.0 m
(d) 1.25 m
8. A current loop ABCD is held fixed on the plane
of the paper as shown in the figure. The arcs BC
(radius = b) and DA (radius = a) of the loop are
joined by two straight wires AB and CD.  A
steady  current I is flowing in the loop. Angle
made by AB and CD at the origin O is 30°.
Another straight thin wire with steady current I
1
flowing out of the plane of the paper is kept at
the origin.
The magnitude of the magnetic field (B) due to the loop ABCD at the
origin (O) is :
(a)
(b)
(c)
(d) zero
9. A galvanometer of resistance, G is shunted by a resistance S ohm. To
keep the main current in the circuit unchanged, the resistance to be put
in series with the galvanometer is
(a)
(b)
(c)
(d)
10. A beam of electrons is moving with constant velocity in a region having
simultaneous perpendicular electric and magnetic fields of strength 20
Vm
–1
 and 0.5 T respectively at right angles to the direction of motion of
the electrons. Then the velocity of electrons must be
(a) 8 m/s
(b) 20 m/s
(c) 40 m/s
(d)
11. A current I flows in an infinitely long wire with cross section in the
form of a semi-circular ring of radius R. The magnitude of the magnetic
induction along its axis is:
(a)
(b)
(c)
(d)
Page 5


PART-I (Single Correct MCQs)
1. Two long parallel wires carry currents i
1
 andn i
2
 such that i
1
 > i
2
. When
the currents are in the same direction, the magnetic field at a point
midway between the wires is 6 × 10
–6
 T. If the direction of i
2
 is
reversed, the field becomes 3 × 10
–5
 T. The ratio of  is
(a)
(b) 2
(c)
(d)
2. A wire carrying current I has the shape as shown in adjoining figure.
Linear parts of the wire are very long and parallel to X-axis while
semicircular portion of radius R is lying in Y-Z plane. Magnetic field at
point O is :
(a)
(b)
(c)
(d)
3. A closely wound solenoid of 2000 turns and area of cross-section 1.5 ×
10
–4
 m
2 
carries a current of 2.0 A. It suspended through its centre and
perpendicular to its length, allowing it to turn in a horizontal plane in a
uniform magnetic field 5 × 10
–2
 tesla making an angle of 30° with the
axis of the solenoid. The torque on the solenoid will be:
(a) 3 × 10
–2
 N-m
(b) 3 × 10
–3
 N-m
(c) 1.5 × 10
–3
 N-m
(d) 1.5 × 10
–2
 N-m
4. An alternating electric field, of frequency v, is applied across the dees
(radius = R) of a cyclotron that is being used to accelerate protons (mass
= m). The operating magnetic field (B) used in the cyclotron and the
kinetic energy (K) of the proton beam, produced by it, are given by :
(a) and K = 2mp
2
?
2
R
2
(b) and K = m
2
p?R
2
(c) and K = 2mp
2
?
2
R
2
(d) and K = m
2
p?R
2
5. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 ×
10
–4
 ampere gives a deflection of one per division. To convert this
galvanometer into a voltmeter having a range of 25 volts, it should be
connected with a resistance of
(a) 2450 ? in series
(b) 2500 ? in series.
(c) 245 ? in series.
(d) 2550 ? in series.
6. In the adjoining figure, two very long, parallel wires A and B
carry currents of 10 ampere and 20 ampere respectively, and
are at a distance 20 cm apart. If a third wire C (length 15 cm)
having a current of 10 ampere is placed between them, then
how much force will act on C ? The direction of current in all
the three wires is same.
(a) 3 × 10
–5
 N (left)
(b) 3 × 10
–5
 N (right)
(c) 6 × 10
–5
 N (left)
(d) 6 × 10
–5
 N (right)
7. A 2 µC charge moving around a circle with a frequency of 6.25 × 10
12
Hz produces a magnetic field 6.28 tesla at the centre of the circle. The
radius of the circle is
(a) 2.25 m
(b) 0.25 m
(c) 13.0 m
(d) 1.25 m
8. A current loop ABCD is held fixed on the plane
of the paper as shown in the figure. The arcs BC
(radius = b) and DA (radius = a) of the loop are
joined by two straight wires AB and CD.  A
steady  current I is flowing in the loop. Angle
made by AB and CD at the origin O is 30°.
Another straight thin wire with steady current I
1
flowing out of the plane of the paper is kept at
the origin.
The magnitude of the magnetic field (B) due to the loop ABCD at the
origin (O) is :
(a)
(b)
(c)
(d) zero
9. A galvanometer of resistance, G is shunted by a resistance S ohm. To
keep the main current in the circuit unchanged, the resistance to be put
in series with the galvanometer is
(a)
(b)
(c)
(d)
10. A beam of electrons is moving with constant velocity in a region having
simultaneous perpendicular electric and magnetic fields of strength 20
Vm
–1
 and 0.5 T respectively at right angles to the direction of motion of
the electrons. Then the velocity of electrons must be
(a) 8 m/s
(b) 20 m/s
(c) 40 m/s
(d)
11. A current I flows in an infinitely long wire with cross section in the
form of a semi-circular ring of radius R. The magnitude of the magnetic
induction along its axis is:
(a)
(b)
(c)
(d)
12. A very long straight wire carries a current I. At the instant when a
charge + Q at point P has velocity , as shown, the force on the charge
is
(a) along OY
(b) opposite to OY
(c) along OX
(d) opposite to OX
13. A particle of mass m and charge q, accelerated by potential difference
V enters a region of uniform transverse magnetic field B. If d is the
thickness of region of magnetic field, then the deviation of the particle
from initial direction when it leaves the field is
(a)
(b)
(c)
(d) zero
14. A long insulated copper wire is closely wound as a spiral of ‘N’ turns.
The spiral has inner radius ‘a’ and outer radius ‘b’. The spiral lies in the
XY plane and a steady current ‘I’ flows through the wire. The Z-
component of the magnetic field at the centre of the spiral is