Physics - Magnetic Effects of Currents
Exam Duration: 45 Mins Total Questions : 30
A galvanometer can be used to measure voltage drop when it is connected with
- (a)
high resistance in series with it
- (b)
a high resistance in parallel with it
- (c)
a low resistance in series with it
- (d)
a low resistance in parallel with it
If h and e denote Planck's constant and electronic charge respectively, then h/e has unit of
- (a)
magnetic flux
- (b)
magnetic flux density
- (c)
electric flux
- (d)
electric flux density
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
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 voltmeter has a range of 5_0 V and bears the description 2000 \(\Omega \)/volt. The resistance needed to convert it into a 15V range voltmeter is
- (a)
1000 \(\Omega \) in series
- (b)
2000 \(\Omega \) in series
- (c)
6000 \(\Omega \) in series
- (d)
20000 \(\Omega \) in series
A circular loop of radius R carrying a current I is placed in a un9iform magnetic field with its plane perpendicular to B. The force on the loop is
- (a)
2\(\pi \)RIB
- (b)
2\(\pi \)RI2B2
- (c)
4\(\pi \)RIB
- (d)
zero
A moving coil voltmeter is generally used in the laboratory to measure the potential difference across a conductor of resistance r carrying current I. Voltmeter has resistance R and will measure the potential difference more correctly as
- (a)
R approaches r
- (b)
R < r
- (c)
R > r
- (d)
R = 0
If a current is passed in a spring, it
- (a)
gets compressed
- (b)
gets expanded
- (c)
oscillates
- (d)
remains as it is
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
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
XA proton of mass 1.67X10-27 kg and charge 1.6X10-19 is projected with a speed of 2X106 ms-1 at an angle 600 to the x-axis. If a uniform magnetic field of 0.104 tesla is applied along y-axis, the path of proton is
- (a)
a circle of radius = 0.2 m and time period = \(2\pi \times { 10 }^{ -7\quad }s\)
- (b)
a circle of radius = 0.1 m and time period = \(2\pi \times { 10 }^{ -7\quad }s\)
- (c)
a helix of radius = 0.1 m and time period =\(2\pi \times { 10 }^{ -7\quad }s\)
- (d)
a helix of radius = 0.2 m and time period =\(2\pi \times { 10 }^{ -7\quad }s\)
A long staright wire along the z-axis carries a current I in the negative z-direction. The magnetic vector field \(\vec { B } \) at a point having coordinates (x,y) i the z=0 plane is
- (a)
\(\frac { { \mu }_{ 0 }{ I(y\hat { i } -x\hat { j) } } }{ 2\pi ({ x }^{ 2 }+{ y }^{ 2 }) } \)
- (b)
\(\frac { { \mu }_{ 0 }{ I } }{ 2\pi } .\frac { (x\hat { i } +y\hat { j } ) }{ ({ x }^{ 2 }+{ y }^{ 2 }) } \)
- (c)
\(\frac { { \mu }_{ 0 }{ I } }{ 2\pi } .\frac { (x\hat { j} -y\hat { i } ) }{ ({ x }^{ 2 }+{ y }^{ 2 }) } \)
- (d)
\(\frac { { \mu }_{ 0 }{ I } }{ 2\pi } .\frac { (x\hat { j} +y\hat { i } ) }{ ({ x }^{ 2 }+{ y }^{ 2 }) } \)
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
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
Two long parallel wires are at a distance 2d apart. They carry steady equal current flowing out of the plane of the paper as shown. The variation of the magnetic field along the line XX' is given by
- (a)
- (b)
- (c)
- (d)
A current i flows along the length of an infinitely long straight, thin walled pipe. Then,
- (a)
the magnetic field is zero only on the axis of the pipe
- (b)
the magnetic field is different at different points inside the pipe
- (c)
the magnetic field at any point inside the pipe is zero
- (d)
the magnetic field at all points inside the pipe is the same but not zero