1.State any three important properties of magnetic field lines.
2.Why do magnetic field lines form continuous closed loops, unlike electric field lines?
3.Write the expression for the magnetic field at a point on the axial line and equatorial line of a short bar magnet.
4.Explain how a current-carrying solenoid behaves like a bar magnet. Mention one similarity and one difference.
5.Write the formula for the torque acting on a magnetic dipole of moment $\vec{m}$ placed in a uniform magnetic field $\vec{B}$. When is this torque maximum?
6.A short bar magnet placed with its axis at $30^\circ$ to a uniform magnetic field of $0.25\text{ T}$ experiences a torque of $4.5 \times 10^{-2}\text{ J}$. Calculate the magnitude of its magnetic moment.
7.Calculate the work done in rotating a magnet of magnetic moment $3.0\text{ A m}^2$ through an angle of $60^\circ$ from its position of stable equilibrium in a uniform magnetic field of $0.1\text{ T}$.
8.A magnetic dipole is placed in a uniform magnetic field. Under what condition is its potential energy (i) minimum and (ii) maximum?
9.Two identical magnetic dipoles, each of magnetic moment $m$, are placed at an angle of $90^\circ$ to each other. Find the net magnetic moment of the combination.
10.What is the net magnetic force acting on a bar magnet placed in a uniform magnetic field? Explain.
11.A bar magnet of magnetic moment $1.5\text{ J/T}$ lies aligned with the direction of a uniform magnetic field of $0.22\text{ T}$. What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment opposite to the field direction?
12.State Gauss's Law in Magnetism.
13.What fundamental physical reality is signified by the equation $\oint \vec{B} \cdot d\vec{S} = 0$?
14.If magnetic monopoles existed, how would the mathematical expression for Gauss's law in magnetism be modified?
15.A closed Gaussian surface encloses a small bar magnet. What is the net magnetic flux leaving the surface? Justify your answer.
16.Contrast Gauss's law for electrostatics with Gauss's law for magnetism. Why is the right-hand side of the equation different?
17.Define magnetic declination at a place.
18.Define angle of dip (or magnetic inclination) at a place.
19.Name the three elements of Earth's magnetic field required to completely specify the magnetic field at a given location.
20.A compass needle free to turn in a vertical plane is taken to the magnetic north pole. How will it orient itself?
21.The horizontal component of Earth's magnetic field at a place is $\sqrt{3}$ times the vertical component. What is the angle of dip at that place?
22.In the magnetic meridian of a certain place, the horizontal component of Earth's magnetic field is $0.26\text{ G}$ and the dip angle is $60^\circ$. What is the magnitude of the total magnetic field of the Earth at this location?
23.How does the angle of dip vary as one moves from the magnetic equator to the magnetic poles?
24.At a certain location in Africa, a compass points $12^\circ$ west of the geographic north. What does this angle represent?
25.If the angle of dip at a place is zero, what can you say about the vertical component of Earth's magnetic field there? Where on Earth does this happen?
26.A ship is sailing due west according to the mariner's compass. If the declination of the place is $15^\circ$ east of north, what is the true (geographic) direction of the ship?
27.Distinguish between diamagnetic and paramagnetic materials on the basis of their magnetic susceptibility ($\chi$).
28.How does the relative magnetic permeability ($\mu_r$) vary for diamagnetic, paramagnetic, and ferromagnetic materials?
29.What is the Meissner effect in superconductors? Why are superconductors considered perfect diamagnets?
30.State Curie's Law for paramagnetic materials. Write its mathematical form.
31.Define Curie Temperature ($T_C$). What happens to a ferromagnetic material when it is heated above its Curie temperature?
32.Classify the following materials into diamagnetic, paramagnetic, and ferromagnetic: Bismuth, Copper, Iron, Aluminum, Nickel, Water.
33.Why does a diamagnetic substance develop a weak magnetization in a direction opposite to the applied magnetic field?
34.How does the magnetic susceptibility of a diamagnetic material depend on temperature?
35.Draw a diagram to show the behavior of magnetic field lines when a diamagnetic specimen is placed in a uniform magnetic field.
36.Draw a diagram to show the behavior of magnetic field lines when a ferromagnetic specimen is placed in a uniform magnetic field.
37.The susceptibility of a magnetic material is $-2.6 \times 10^{-5}$. Identify the type of magnetic material and state its behavior in a non-uniform magnetic field.
38.What is a magnetic hysteresis loop? What physical quantity does the area under the B-H curve represent?
39.Define the terms 'Retentivity' and 'Coercivity' of a magnetic material.
40.Why is soft iron preferred over steel for making the cores of transformers and electromagnets?
41.What specific properties (in terms of retentivity and coercivity) are required for a material to be used for making a permanent magnet?
42.State the key differences between the hysteresis loops of soft iron and steel.
43.Name any two alloys commonly used for manufacturing permanent magnets.
44.Mention two practical ways by which a permanent magnet can be demagnetized.
45.Why does the magnetization of a ferromagnetic material not increase indefinitely with an increasing external magnetic field ($H$)? Explain briefly in terms of domains.
46.An electromagnet is to be used in a crane to lift heavy iron scrap. Should its core have high or low coercivity? Justify.
