Q: Write two properties of a material suitable for making (a) a permanent magnet and (b) an electromagnet

Permanent Magnets:\$1)\$ High Retentivity: Magnet should be strong\$2)\$ High coercivity: Magnetisation should not get affected by stray Magnetic fieldsElectromagnets:\$1)\$ High Permeability core of Iron for easy magnetisation\$2)\$ Low Retentivity: For easy magnetisation/demagnetisation.

Q: A bar magnet is demagnetized by inserting it inside a solenoid of length \$0.2m, 100turas\$, and carrying a current of \$5.2A\$. The coercivity of the bar magnet is:

Coercivity \$= H = \dfrac{B}{\mu_0}\$\$ni = \dfrac{N}{\ell}i = \dfrac{100}{0.2}\times 5.2\$\$=2600 A/m\$

Question 1

What is hysteresis? Define the terms 'coercivity' and 'retentivity' of a ferromagnetic material.

Accepted Answer

Hysteresis: The phenomenon in which the magnetic induction ($\vec { B } $) lags behind with respect to the magnetizing field $\vec { H } $ is called hysteresis.It occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely.Retentivity: The property of the magnetic material to retain magnetism even in the absence of the magnetizing field is known as retentivity or remanence.Coercivity: The magnetizing field (H) needed to demagnetize the magnetic material completely is known as its coercivity.

Question 2

Magnetic field lines of two magnets are shown in fig. A and fig. B. Select the figure that represents the correct pattern of field lines. Give reasons for your answer. Also, name the poles of the magnets facing each other.

Accepted Answer

R.E.F image  Solution : In the given figure A & B The figure B is the correct Pattern of field lines.Reason : Magnetic lines of forces never intersect to each other (it is the propertiys of magnetic lines of forces)So, the figure A is is not correct

Question 3

State four properties of magnetic field lines.

Accepted Answer

The four properties of magnetic field lines are as follows:1. They are closed and continuous curves.2. They are directed from the north pole outside the magnet towards the south pole of the magnet.3. The tangent at any point on a field line gives the direction of magnetic field at that point.4. Parallel and equi-distant filed lines represent a uniform magnetic field. The earth&#8217;s magnetic field in a limited space is uniform.

Question 4

Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another pole.

Accepted Answer

The magnetic filed lines are the lines draw in a magnetic field along which a north magnetic pole would move. The magnetic lines are also known as magnetic lines of force.Activity to draw a magnetic field line outside a bar magnet from one pole to another pole.Take the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.Mark the boundry of the magnet.Place the compass near the pole of the magnet. The south pole of the needle points toward the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.Mark the position of two ends of the needle.Now move the needle to a new position such that its south that its south pole occupies the position previously occupied by its north pole.In this way, proceed step by step till you reach the south pole of the magnet.Join the point marked on the paper by a smooth curve. This curve represents a magnetic field line.

Question 5

State the direction of magnetic field in the following case.

Accepted Answer

Perpendicular to the plane of paper in the outward direction by using Fleming&#8217;s left hand rule.

Question 6

(a) Draw the pattern of magnetic field lines near a bar magnet placed with its north pole pointing towards the geographic north. Indicate the position of neutral points by marking x.
(b) State whether the magnetic field lines in part (a) represent a uniform magnetic field or non-uniform magnetic field?

Accepted Answer

(a) The position of neutral points are as follows as the figure below.(b) The magnetic field lines as shown in part (a) are non-uniform.

Question 7

Write two properties of a material suitable for making (a) a permanent magnet and (b) an electromagnet

Accepted Answer

Permanent Magnets:$1)$ High Retentivity: Magnet should be strong$2)$ High coercivity: Magnetisation should not get affected by stray Magnetic fieldsElectromagnets:$1)$ High Permeability core of Iron for easy magnetisation$2)$ Low Retentivity: For easy magnetisation/demagnetisation.

Question 8

A bar magnet is demagnetized by inserting it inside a solenoid of length $0.2m, 100turas$, and carrying a current of $5.2A$. The coercivity of the bar magnet is:

Accepted Answer

Coercivity $= H = \dfrac{B}{\mu_0}$$ni = \dfrac{N}{\ell}i = \dfrac{100}{0.2}\times 5.2$$=2600 A/m$

Question 9

Magnetic field lines are shown in the given diagram. A student makes a statement that magnetic field at X is stronger than at Y. Justify this statement. Also redraw the diagram and mark the direction of magnetic field lines.

Accepted Answer

The relative strength of the magnetic field is shown by the degree of closeness of the field lines. The degree of closeness is more at X than at Y. Therefore, the field is stronger at X where the field lines are crowded.

Question 10

In a permanent magnet at room temperature.

Accepted Answer

A permanent magnet at room temperature retains a ferromagnetic property that possesses a dipole moment. And domains are partially aligned due to thermal agitation.The correct option is C.

Magnetic Hysteresis and Hysteresis Loss- II

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Magnetic Hysteresis and Hysteresis Loss Part I