Physics - Magnetic Effects of Currents
Exam Duration: 45 Mins Total Questions : 30
The sensitiveness of a moving coil galvonometer can be increased by
- (a)
decreasing the area of the coil
- (b)
decreasing the number of turns in the coil
- (c)
increasing the area of the coil
- (d)
increasing the strength of the current
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
Two infinite long wires at a distance of 1 m carry current of 1 mA in the same direction. Which one of the following is CORRECT?
- (a)
The given two wires repel each other
- (b)
Both wires experiences a force exactly equal to 2 X 10-7 Nm-1
- (c)
One of the two wires is replaced by an electron beam, then beam will not get deflected
- (d)
NONE OF THESE
The magnetic field at the centre of a circular coil carrying current is
- (a)
smaller, smaller the radius of the coil
- (b)
greater, smaller the radius of the coil
- (c)
directly proportional to the cube of the radius
- (d)
inversely proportional to the cube of the radius
Two conducting wires placed parallel to each other carry current in the same direction. If the distance between them is halved, the force between them will be
- (a)
halved
- (b)
doubled
- (c)
increased four-fold
- (d)
decreased by a factor one-quarter
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
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
Two circular coils of wire carrying currents and of radii 20 cm and 40 cm are connected in parallel. The ratio of the magnetic fields at their centres is
- (a)
4:1
- (b)
1:4
- (c)
2:1
- (d)
1:2
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
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
What should be the amount of current through the ring of radius 5 cm so that field in the centre is equal with earth's magnetic field of 7 X 10-5 Wb m-2 is
- (a)
0.28 A
- (b)
0.5 A
- (c)
2.8 A
- (d)
NONE OF THESE
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
In hydrogen atom the electron is making 6.6 X 1015 rev/sec, around the nucleus in an orbit of radius 0.528 \(\mathring { A } \). The magnetic moment (A m2) is
- (a)
1 X 10-15
- (b)
1 X 10-10
- (c)
1 X 10-23
- (d)
1 X 10-27
A proton and a deutron both having the same kinetic energy, enter perpendicularly into a uniform magnetic field B. For motion of proton and deutron on circular path of radius Rp and Rd respectively, the correct statement is
- (a)
Rd=Rp
- (b)
Rd=2Rp
- (c)
Rd=\(\sqrt { 2 } \)Rp
- (d)
Rd=Rp/\(\sqrt { 2 } \)
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)
\(\frac { { \mu }_{ 0 }{ I } }{ 2\pi } .\frac { (x\hat { j} +y\hat { i } ) }{ ({ x }^{ 2 }+{ y }^{ 2 }) } \)
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)
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
A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be
- (a)
nB
- (b)
n2B
- (c)
2nB
- (d)
2n2B