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UNIT-III, MAGNETIC EFFECT OF CURRENT AND MAGNETISM
Formula
Very Short Answer Type Question (1 Mark)
1. What is the magnitude of the force when a charge particle(q) remain stationary in the
magnetic field B.
2. Define ‘ flux density’. State its S.I. unit.
3. Why two parallel wires carrying current in the same direction attract each other.
4. Give the relation between relative permeability and susceptibility.
5. Under what condition an electron moving through a magnetic field experiences maximum
force?
6. Why electron is not used for cyclotron. Give main reason?
7. What is the magnetic field at the point O in the given diagram, due to the current carrying
conductor in the given figure:
i
O
8. How can we convert a galvanometer into an ammeter?
i
9. How can you identify para magnetic and ferromagnetic materials on the basis of magnetic
susceptibility?
10. What is the angle of dip at a place where Bv and BH are equal?
11. A coil of unit area and 2 turns in which 5 ampere current passes. Find its magnetic dipole
moment.
12. What type of material used for core of transformers?
Short Answer type ( 2 marks )
1. The force F experienced by a particle of charge q moving with velocity v in a magnetic field B
is given by F = q (v x B). of these, name the pairs of vectors which are always at right angles
to each other.
2. What is the advantage of using radial magnetic field in a MCG?
3. Which one of the following will describe smaller circle when projected with same velocity v
perpendicular to the magnetic field B: (i) α particle (ii) β particle.
4. What do you mean by magnetic dipole moment? State its expression.
5. A stream of electrons, travelling with a speed v at right angles to a uniform magnetic field B,
is deflected in a circular path of radius r. Prove that e/m = v / (rB).
6. An ammeter and a milli ammeter are converted from the same galvanometer. Out of the
two, which current measuring instruments have higher resistance?
7. A magnetized needle is placed 300 with the direction of a uniform magnetic field of intensity
3 x 10-2T. The torque acting on the needle is 7.2 x 10-4 J. Calculate the magnetic moment of
the needle.
8. Define angle of dip. Deduce the relation connecting the angle of dip and the horizontal
component of the earth’s magnetic field at a place.
9. A magnetic needle, free to rotate in a particular position, orients itself with its axis horizontal
at a certain place on the earth. What are the values of (i) angle of dip (ii) horizontal
component of earth’s field at this place?
3 Marks questions
1. Derive an expression for the torque on a rectangular coil of area A, carrying a current I
placed in a magnetic field B. The angle between the direction of B and the vector
perpendicular to the plane of the coil is θ.
2. Using Biot-Savart’s law, derive the expression for the magnetic field at the centre of a
circular coil of radius r, having N number of turns. Indicate the direction of the magnetic
field.
3. Derive an expression for the force acting on a current-carrying conductor placed in a uniform
magnetic field. Name the rule which gives the direction of force. Write the condition for
which force becomes (i) maximum, (ii) minimum.
4. With the help of a labeled diagram, explain the principle and working of a moving coil
galvanometer.
5. Depict the magnetic field lines due to two straight long parallel conductors carrying currents
I1 and I2 in the same direction. Hence deduce an expression for the force acting per unit
length on one conductor due to the other. Is this force attractive or repulsive?
6. Give the statement of Curie’s Law. How does the magnetic property of iron change with
increase of temperature?
7. How does the angle of dip vary as one moves from the equator towards the north pole? If
the horizontal component of earth’s magnetic field at a place, where the angle of dip is 600,
is 0.4 x 10-4 T, calculate the vertical component and the resultant magnetic field of the earth
at that point.
8. State Amperes circuital law. Use it to derive the expression for the magnetic field inside a
current carrying toroid of radius R.
9. Using Ampere’s circuital law, find an expression for the magnetic field at a point on the axis
of a long solenoid with closely wounded turns.
Long Answer Type ( 5 marks)
1. Explain with the help of a labeled diagram, the construction, principle and working of a
cyclotron. Derive an expression for time period of revolution and cyclotron frequency. What
is the resonance condition? Give one of its limitations
2. What is the relationship between current and the magnetic moment of a current carrying
circular loop? Deduce an expression for magnetic dipole moment of an electron revolving
around a nucleus in a circular orbit. Indicate the direction of magnetic dipole moment of an
electron moving in a circle and related angular momentum.
3. Derive an expression for the force per unit length between two long straight parallel current
carrying conductors. Hence define SI unit of current.
The conductor XY is free to move and carries a current ‘I’. X
Y
Calculate magnitude and direction of ‘I’
for which magnetic repulsion balances
5mm
-2
the weight. Mass per unit length of XY = 10 kg/m
75A
P
Q
4. Distinguish between magnetic properties of dia, para and ferro magnetic substances in
terms of susceptibility, permeability and coercivity. Which magnetic properties of soft iron
are exploited when used it as an electro magnet.
FORMULA BASED NUMERICALS
01. A current of 5A flows through a 10 turns coil of radius 7cm. The coil lies in x-y plane. What is
the magnitude and direction of dipole moment associated? If this is placed in uniform field
directed along x-axis, in which plane the coil lie when in equilibrium?
02. A coil of ‘n’ turns and radius ‘R’ carries a current of ‘I’. It is unwound and rewound to make
another coil of radius R/2 carrying same current. Calculate the ratio of magnetic moment of
this coil to original.
03. A semicircular coil of arc of radius 20cm carries a current of 10A. Calculate the magnetic field
at the centre of the arc.
04. A wire carries a current of 4A
0.2m
*proton
A proton travels with speed 4*106m/s.
Calculate magnitude and direction of
the force on the proton.
05. A short bar magnet is placed with its axis at 300 with a magnetic field of strength 0.2T
experiences a torque 0.06Nm. (i) Calculate magnetic moment. (ii) What orientation would
corresponds to most stable equilibrium?
06. At a place H = 0.4*10-2 T, angle of dip = 300. Calculate ‘V’ and total intensity of earth’s
magnetic field.
07. A short bar magnet is placed with its axis inclined at an angle 300 to external field of 800G
experiences a torque of 0.016Nm. Calculate (i) Moment of the magnet.
(ii) Work done by an external force in rotating the magnet from most stable position to
most unstable position.
8. A circular coil of 100 turns, radius 10cmcarries a current of 5A. it is suspended vertically in a
uniform horizontal magnetic field of 0.5T. The field lines are making an angle 600 with the
plane of coil. Calculate the magnitude of torque that must be applied on it to prevent it from
turning.
9. A solenoid of 500 turns/m having radius of each turn 10cm is carrying a current of 3A.
Calculate the magnitude of field intensity inside it. If a straight wire of 3cm carrying 10A
current is placed inside solenoid ar to its axis. Calculate force on it.
10. An electron emitted by a heated cathode and accelerated by a PD of 2 kV, enters a region
with a uniform magnetic field of 0.15T ar to field. Determine radius of circular path. What
is change in kinetic energy when electron competes 1 rotation.
Value Based Question:
1. While watching Discovery Channel, Sheela was impressed that certain organisms have
the ability to sense the field lines of earth’s magnetic field. They use this ability to travel
from one location to another. Sheela wanted to find the angle of dip at her place. She
got a magnetic compass, using which she found the magnetic meridian. She then
mounted the compass on a cardboard and placed it vertically along the magnetic
meridian. She was able to measure the angle of dip.
(i)
What values did Sheela have?
(ii)
Define the magnetic elements of the earth.