UNIT
3 MAGNETISM
2025
1. The
relative permeability of substance ‘X’ is slightly less than one and that of
substance ‘Y’ is slightly more than one. Then:
(a) ‘X’ is paramagnetic and ‘Y’ is
ferromagnetic.
(b) ‘X’ is diamagnetic and ‘Y’ is
ferromagnetic.
(c) ‘X’ is paramagnetic and ‘Y’ is
diamagnetic.
(d) ‘X’ is diamagnetic and ‘Y’ is
paramagnetic.
2. A
student has made connections, as shown in Figure 2 below, so that the wires MN
and ST repel each other. But it is observed that they are attracting each
other. What change should the student make for the wires to repel each other?
(a) Reverse the terminals of
batteries E1 and E2.
(b) Reverse the terminals of battery
E1 or E2.
(c) Choose supply voltage such that
E1 = E2.
(d) Add key and ammeter to the
circuit.
3. Magnetic
field at the centre of a circular coil is B. Calculate the magnetic field at
the same point when each of the current, number of turns of the coil and its
radius is doubled.
4. A
galvanometer having a resistance of 20 Ω shows a full scale deflection with a
current of 1 mA. How can it be converted into a voltmeter with a range of 0–10
V?
5. Two
infinitely long straight wires PQ and RS carrying currents I1 and I2
respectively are kept 10 cm apart in vacuum. Calculate magnetic field (B) at
the point X shown in Figure 8 below.
6. An
electron and a proton are moving along the +X axis. If an external magnetic
field B = 0.314 T is applied along −Z axis: (a) What is the path followed by
the electron due to the magnetic field? (b) Calculate the frequency of
revolution of the proton.
2024
7. Lorentz
force in vector form is
8. Assertion:
When an electric current is passed through a moving coil galvanometer, its coil
gets deflected.
Reason: A circular coil produces a
uniform magnetic field around itself when an electric current is passed through
it.
9. Explain
the meaning of the following statement: Curie temperature for soft iron is
770°C.
10. Using
Biot-Savart law, find out the expression for magnetic flux density ‘B’, at the centre of a
current carrying circular coil of radius R.
11. Figure
4 below shows an infinitely long metallic wire YY’ which is carrying a current
I’. P is a point at a perpendicular distance r from it.
(i)
What is the direction of magnetic flux
density B of the magnetic field at the point P?
(ii)
What is the magnitude of magnetic flux
density B of the magnetic field at the point P?
(iii)
Another metallic wire MN having length l
and carrying a current I is now kept at the point P. If the two wires are in
vacuum and parallel to each other, how much force acts on the wire MN due to
the current I’ flowing in the wire YY’?
2023
12. A
circular coil has radius ‘r’, number of turn ‘N’ and carried a current ‘I’.
Magnetic flux density ‘B’ at its centre is:
13. A
long straight wire AB carries a current of 5A. P is a proton travelling with a
velocity of 2 × 106 m/s, parallel to the wire, 0.2 m from it and in
a direction opposite to the current, as shown in Figure 2 below. Calculate the
force which magnetic field of the current carrying conductor AB exerts on the
proton.
14. A
moving coil galvanometer of resistance 55 W produces a full scale deflection
for a current of 250 mA. How will you convert it into an ammeter having a range
of 0 – 3A?
15. Using
Ampere’s circuital law, obtain an expression for magnetic flux density ‘B’ at a
point near an infinitely long and straight conductor, carrying a current I.
2022
16. SI
unit of magnetic dipole moment is:
(a) Am (b) Am2 (c)
Hm–1 (d) Wbm–2
17. The
point P is at a perpendicular distance of 0.2 m from a long straight wire YY’,
which carries a current of 1.6 A, as shown in Figure 1 below.
Magnetic flux density of the magnetic
field at point P is:
(a) 1.6 × 10–6 T directed
into the paper.
(b) 1.6 × 10–6 T coming
out of the paper.
(c) 0.8 × 10–6 T directed
into the paper.
(d) 0.8 × 10–6 T coming
out of the paper.
18. A
proton is moving in a uniform magnetic field B with a velocity v at an angle q
with the field. The force acting on the proton is minimum when q is:
(a) 120° (b) 90° (c)
60° (d) Zero
2019
19. A
rectangular loop of area 5 m2 , has 50 turns and carries a current
of 1 A. It is held in a uniform magnetic field of 0.1 T, at an angle of 30°.
Calculate the torque experienced by the coil.
20. An
a.c. source of emf e = 200 sin ωt is connected to a resistor of 50Ω. Calculate:
(1) Average current (Iavg). (2) Root mean square (rms) value of emf.
2018
21. A
circular coil carrying a current I has radius R and number of turns N. If all
the three, i.e., the current I, radius R and number of turns N are doubled,
then, magnetic field at its Centre becomes:
(a) Double
(c) Four times (b) Half (d) One fourth
22. How
will you convert a moving coil galvanometer into a voltmeter?
23. A
rectangular coil having 60 turns and area of 0.4 m2 is held at right angle to a
uniform magnetic field of flux density 5×10–5T. Calculate the magnetic flux
passing through it.
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