IISER Physics - Magnetic Effects of Currents
Exam Duration: 45 Mins Total Questions : 30
An electron is injected into a region of uniform magnetic field of induction with its velocity inclined to the field. The path of the electron is a
- (a)
circle
- (b)
parabola
- (c)
linear
- (d)
helix
A circular coil carrying current has magnetic induction B at its centre C. The radius of the coil is 3 cm. The distance of a point P from C, where the induction reduces to \(\frac { B }{ 8 } \) would be
- (a)
\(\sqrt { 3 } \)
- (b)
2\(\sqrt { 3 } \)
- (c)
3\(\sqrt { 3 } \)
- (d)
9
The electron of Bohr orbit of hydrogen atom revolves in its innermost orbit round the proton. The magnetic induction at the proton is of the order of
- (a)
1 T
- (b)
10 T
- (c)
100 T
- (d)
1000 T
Cosmic ray particles from outer space enter the earth's atmosphere. On entering the earth's magnetic field, the positively charged particles in the cosmic rays will get deflected towards
- (a)
North
- (b)
East
- (c)
West
- (d)
South
An electron is moving in XY-plane, making an angle \(\theta \) relative to the positive X-axis. The specific charge of electron is 1.78 X 1011 C kg-1. A uniform magnetic field of induction 0.8 Wbm-2 acts along the positive X-axis. Then the particle will pass periodically through thye x-axis with a period
- (a)
1.406 X 1011 s
- (b)
2.198 X 1011 s
- (c)
4.465 X 1011 s
- (d)
0.711 X 1011 s
An electrical instrument P is connected in series with a galvanometer G. A small resistance placed
- (a)
parallel with G will increase the sensitivity of P
- (b)
parallel with G will reduce the sensitivity of P
- (c)
in series with G will change the sensitivity of P
- (d)
in series with P will change the sensitivity of both P and G
The principle of moving coil galvanometer is based on the action that a (coil) wire carrying current.
- (a)
produces a magnetic field causing deflection
- (b)
produces an electric field causing deflection of the coil
- (c)
experiences a torque due to the presence of magnetic field
- (d)
experiences a translational (mechanical) force in the magnetic field
A wire carries a steady current of 2.4 A. A straight section of the wire, with a length of 0.75 m along the x-axis, lies within a uniform magnetic field, \(\vec { B } =(1.6\hat { k)T. } \) If the current flows in the +x-direction, the magnetic force on the section of wire is
- (a)
2.88 \(\hat { j } \) N
- (b)
-2.88 \(\hat { j } \) N
- (c)
2.88 \(\hat { k } \) N
- (d)
-2.88 \(\hat { k } \) N
The coil of a galvanometer movement has an area of 1.0 cm2 and cosists of 100 turns of fine wire. The radial magnetic field at the position of the coil is 0.15 T, and the torsional constant of the spring is c=1.5X10-7 Nm deg-1. The angular deflection of the coil for a current of 1 mA is
- (a)
10
- (b)
0.10
- (c)
50
- (d)
100
Assume that the earth's magnetic field is that of a dipole with moment mE = 8.1 X 1022 A.m2. The value of magnetic induction at a point on the earth's surface at the magnetic equator is
- (a)
0.31 X 10-4 T
- (b)
0.31 X 10-6T
- (c)
0.31 X 10-3 T
- (d)
0.31 X 105T
A steady current is flowing through a conductor of uniform cross-section. Any segment of the conductor has
- (a)
zero charge
- (b)
only positive charge
- (c)
only negative charge
- (d)
charge proportional to current
A length L of a wires carriers a steady current I. It is bent first to form circular plane coil of one turn. The same length is now bent more sharply to give a double loop of small radius. The magnetic field field at the centre caused by the same current is
- (a)
a quarter of its first value
- (b)
four times of its first value
- (c)
a half of its first value
- (d)
unaltered
A current flows along the length of an infinity long straight thin walled pipe. Then
- (a)
the magnetic field at all points inside the pipe is same but not zero
- (b)
the magnetic field at any point inside the pipe is zero
- (c)
the magnetic field is zero only on the axis of the pipe
- (d)
the magnetic field is different at different points inside the pipe
Electron of mass m and charge e is travelling with a speed \(\vartheta \) along circular path of radius r at right angles to a uniform magnetic field B. If the speed of the electron is doubled and the magnetic field is halved the resulting path would have a radius
- (a)
4r
- (b)
2r
- (c)
r/4
- (d)
r/2
With a resistance R connected in series with a galvanometer of resistance 100 \(\Omega \), it acts as a voltmeter of range 0 to 10 V. To double the range a resistance of 1000 \(\Omega \) is to be connected in series with R. Then the value of R (in \(\Omega \) ) is
- (a)
1100
- (b)
1000
- (c)
900
- (d)
800
Two concentric coplanar circular loops of radii r1 and r2 carry currents of respectively I1 and I2 in opposite direction (one clockwise and other anti-clockwise). The magnetic induction at the centre of the loops is half due to I1 alone at the centre. If r2=2r1, the value of I1/I2 is
- (a)
2
- (b)
1/2
- (c)
1/4
- (d)
1
A proton and an alpha-particle enter a uniform magnetic field perpendicularly with the same speed. If proton takes 25\(\mu \) second to make 5 revolutions, then the periodic time for the alpha-particle would be
- (a)
50\(\mu \)s
- (b)
25\(\mu \)s
- (c)
10\(\mu \)s
- (d)
5\(\mu \)s
A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current I passes through the coil, the magnetic field at the centre is
- (a)
\(\frac { { \mu }_{ 0 }NI }{ b } \)
- (b)
\(\frac { { 2\mu }_{ 0 }NI }{ a } \)
- (c)
\(\frac { { \mu }_{ 0 }NI }{ 2(b-a) } ln\frac { b }{ a } \)
- (d)
\(\frac { { \mu }_{ 0 }{ I }^{ N } }{ 2(b-a) } ln\frac { b }{ a } \)
Assuming that the earth's magnetic field closely resembles the field of a mgnetic dipole, at least for distances out to several Earth radii, the value of the Earth's magnetic moment is
- (a)
8.1 X 1022 A.m2
- (b)
3.5 X 1020 A.m2
- (c)
11.0 X 1021 A.m2
- (d)
7.3 X 1023 A.m2
The variation of magnetic induction (B) with distance (r) from a very long straight conductor carrying a steady current is given by the graph:
- (a)
- (b)
- (c)
- (d)
A long straight wire with a radius R carries a steady current I that is distributed uniformly over the cross-section of the wire. The magnetic induction B(r) varies with distance r. This variation is best shown by one of the graphs:
- (a)
- (b)
- (c)
- (d)
The magnetic permeability can be expressed in the units of
- (a)
Hm-1
- (b)
NA-2
- (c)
T.m.A-1
- (d)
ALL OF THE ABOVE
An element, \(dl=dx\hat { i } \) (where, dx= 1 cm) is placed at the origin and carries a large current i = 10 A. What is the magnetic field on the Y-axis at a distance of 0.5 m?
- (a)
\(2\times { 10 }^{ -8^{ \wedge } }\quad T\)
- (b)
\(4\times { 10 }^{ -8^{ \wedge } }\quad T\)
- (c)
\(-2\times { 10 }^{ -8^{ \wedge } }\quad T\)
- (d)
\(-4\times { 10 }^{ -8^{ \wedge } }\quad T\)
A charge particle of charge q=2C has velocity v=100 m/s. When it passes through point A and has velocity in the direction shown. The strength of magnetic field at point B due to this moving charges is (r= 2m)
- (a)
\(2.5\mu T\)
- (b)
\(5.0\mu T\)
- (c)
\(2.0\mu T\)
- (d)
None of the above
A circular coil A of radius r carries current i. Another circular coil B of radius 2r carries current of i. The magnetic fields at the centres of the circular coils are in the ratio of
- (a)
3:1
- (b)
4:1
- (c)
1:1
- (d)
2:1
A long straight, solid metal wire of radius 2 mm carries a current uniformly distributed over its circular cross-section. The magnetic field induction at a distance 2 mm from its axis is B. Then, the magnetic field induction at distance 1 mm from axis will be
- (a)
B
- (b)
B/2
- (c)
2B
- (d)
B
An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?
- (a)
The electron will be acceleration along the axis
- (b)
The electron path will be circular about the axis
- (c)
The electron will experience a force at 45o to the axis and hence execute a helical path
- (d)
The electron will continue to move with uniform velocity along the axis of the solenoid
Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field \(B={ B }_{ o }\hat { k } \)
- (a)
They have equal Z-components of momenta
- (b)
They must have equal charges
- (c)
They necessarily represent a particle anti- particle pair
- (d)
The charge to mass ratio satisfy \({ \left( \frac { e }{ m } \right) }_{ 1 }+{ \left( \frac { e }{ m } \right) }_{ 2 }=0\)
A charged particle with charge q enters a region of constant, uniform and with a velocity perpendicular to both and and comes out without any change in magnitude or direction of . Then,
- (a)
\(=\times \frac { }{ { B }^{ 2 } } \)
- (b)
\(=\times \frac { }{ { B }^{ 2 } } \)
- (c)
\(=\times \frac { }{ { E }^{ 2 } } \)
- (d)
=\times \frac { }{ { E }^{ 2 } }
A charged particle moves through a magnetic field perpendicular to its direction. Then,
- (a)
the momentum changes but the kinetic energy is constant
- (b)
both momentum and kinetic energy of the particle are not constant
- (c)
both momentum and kinetic energy of the particle are constant
- (d)
kinetic energy changes but the momentum is constant