In this article, we shall study magnetic induction at the point on the magnetic axis and magnetic equator of bar magnet.

Magnetic Induction at a Point on Axis of Bar Magnet:

The line passing through the poles of a bar magnet is called the axis of the magnet. Consider a bar magnet having pole strengths +m & -m and magnetic length to ‘2l’. The magnetic dipole moment vector is given by

M = m × 2l …….. (1)

Its direction is from the south pole to the north pole.

Consider point P on the axis of the magnet at a distance of ‘r’ from the centre of magnet O.

Consider the north pole. Magnetic induction at P due to the north pole is given by

The direction of magnetic induction is away from the north pole and along the axis of the magnet.

Consider the south pole. Magnetic induction at a point on the axis due to the south pole is given by

The direction of magnetic induction is towards the south pole along the axis of the magnet. Let B be the resultant magnetic induction at P

Then,    B = B₁ +  B₂ ………….(4)

This is an expression for magnetic induction at a point on the axis of a bar magnet.

For short bar magnet, l is very less than r. (l << r), hence l can be neglected. (i.e.  l = 0)

This is an expression for magnetic induction at a point on the axis of the short bar magnet.

Magnetic Induction at a Point on Equator of Bar Magnet:

The perpendicular bisector of the segment joining the north pole and south pole of a bar magnet is called equator of the magnet.

Consider a bar magnets having pole strength +m & -m & m.l. 2l the magnetic dipole movement vector is given by

M = m × 2l ………….. (1)

The direction of the magnetic dipole moment is from the south pole to north pole.

Let P be the point on the equator of a bar magnet at a distance of r from the centre of magnet O.

Consider the north pole. Magnetic induction at P due to the north pole is given by

Consider the south pole. Magnetic induction at P due to the south pole is given by

Resolving the magnetic induction B₁ & B₂ along the axis of the magnet and the along the equator of the magnet. The components B₁sinθ and B₂sinθ are equal & opposite hence cancel each other. The component B₁ cos θ and B₂ cos θ are in the same direction where they reinforce (support) each other. Let B be the resultant magnetic induction at P then

This is an expression for Magnetic induction at a point on the equator of the bar magnet.

For short bar magnet (l << r). l is small so can be neglected. (l = 0)

This is an expression for magnetic induction at a point on the equator of a short bar magnet. Its direction is from the north pole to south pole.

Numerical Problems:

Example – 01:

Find the magnetic induction at a point distant 10 cm on the axis of a short bar magnet of moment 0.2 Am².

Given: Distance from centre = r = 10 cm = 0.1 m, Magnetic moment = 0.2 Am². Point on axis.

To Find: B =?

Solution:

Ans: The magnetic induction at the point is 4 x 10^-5 T

Example – 02:

Find the magnetic induction at a point distant 20 cm on the equator of a short bar magnet of moment 5 Am².

Given: Distance from centre = r = 20 cm = 0.2 m, Magnetic moment = 5 Am²., The point on the equator.

To Find: Magnetic induction= B =?

Solution:

Ans: The magnetic induction at the point is 6.25 x 10^-5 T

Example – 03:

Find the magnetic induction at a point 0.5 m from either pole on the equator of a bar magnet of moment 5 Am².

Given: Distance from either pole = 0.5 m, Magnetic moment = 5 Am².

To Find: B =?

Solution:

As the point is equidistant from either pole it is on the equator of the bar magnet

∴ r² + l² = (0.5)² = 0.25

Ans: The magnetic induction at the point is 4 x 10^-6 T

Example – 04:

Find magnetic induction due to a short bar magnet at a point distant 10 cm a) on its axis and b) on its equator, given that the magnetic dipole moment of the magnet is 0.25 Am².

Given: Distance from centre = r = 10 cm = 0.1 m, Magnetic moment = 0.25 Am².

To Find: B_axis =? B_equator =?

Solution:

Ans: The magnetic induction at the point on the axis is 5 x 10^-5 T and

that on the equator is 2.5 x 10^-5 T

Example – 05:

A bar magnet has pole strength 10 Am and a magnetic length of 5 cm. Find B at equidistant point of 10 cm from either pole.

Given: Distance from either pole = 10 cm = 0.1 m, pole strength = m = 10 Am, magnetic length = 2l = 5 cm = 0.05 m

To Find: B =?

Solution:

Magnetic Moment = M = m . 2l = 10 x 0.05 = 0.5 Am²

As the point is equidistant from either pole it is on the equator of the bar magnet

∴ r² + l² = (0.1)² = 0.01

Ans: The magnetic induction at the point is 5 x 10^-6 T

Example – 06:

Find magnetic induction due to a short bar magnet at a point distant 20 cm a) on its axis and b) on its equator, given that the magnetic dipole moment of the magnet is 0.5 Am².

Given: Distance from centre = r = 20 cm = 0.2 m, Magnetic moment = 0.5 Am².

To Find: B_axis =? B_equator =?

Solution:

Ans: The magnetic induction at the point on axis is 1.25 x 10^-5 T and

that on equator is 6.25 x 10^-6 T

Example – 07:

Find the magnetic induction at a point distant 8 cm on the equator from the centre of a short bar magnet of moment 0.2 JT^-1.

Given: Distance from centre = r = 8 cm = 0.08 m, Magnetic moment = 0.2 JT^-1, Point on equator.

To Find: B =?

Solution:

Ans: The magnetic induction at the point is 3.91 x 10^-5 T

Example – 08:

Find the magnetic induction at a point distant 10 cm from the centre of the magnet on the axis of a short bar magnet of moment 0.24 JT^-1.

Given: Distance from centre = r = 10 cm = 0.1 m, Magnetic moment = 0.24 JT^-1. Point on axis.

To Find: B =?

Solution:

Ans: The magnetic induction at the point is 4.8 x 10^-5 T

Example – 09:

Find the magnetic induction due to a bar magnet of magnetic induction 0.5 Am² at a point on its axis at a distance of 15 cm from the nearest pole. The magnetic length of magnet is 10 cm.

Given: Magnetic moment = M = 0.5 Am², distance from nearest pole = 15 cm = 0.15 m, magnetic length = 2 l = 10 cm, l = 5 cm = 0.05 m, distance of point from centre = r = 0.15 + 0.05 = 0.20 m,  μ_o/4π = 10^-7 Wb/Am.

To Find: B_axis =?

Solution:

Ans: The magnetic induction at the point is 1.422 x 10^-5 T

Example – 10:

The magnetic induction at a point on the equator of a magnetic dipole at a distance of 10 cm from its centre is 5 x 10^-5 Wb/m². Calculate the magnetic moment of the magnet.

Given: Distance from centre = r = 10 cm = 0.1 m, Magnetic moment = B = 5 x 10^-5 Wb/m^2, Point on equator.

To Find: Magnetic moment = M =?

Solution:

Ans: The magnetic moment is 0.5 Am²

Example – 11:

The magnetic induction at a point on the axis at a distance 20 cm from the centre of the magnet is 1.5 x 10^-5 Wb/m². Find the magnetic induction at a point on the equator at the same distance from the centre.

Given: distance of point from centre of magnet = r = 20 cm for both the points. Magnetic induction = B_axis = 1.5 x 10^-5 Wb/m²,

To Find: B_equator =?

Solution:

Ans: Magnetic induction at a point on equator is 7.5 x 10^-6 Wb/m².

Example – 12:

The strength of magnetic field at a point on axis of a magnetic dipole at a distance of 10 cm from its centre is 4 x 10^-5 Wb/m². Calculate the magnetic moment of the magnet.

Given: Distance from centre = r = 10 cm = 0.1 m, Magnetic moment = B = 4 x 10^-5 Wb/m^2, Point on axis.

To Find: M =?

Solution:

Ans: The magnetic moment is 0.2 Am²

Example – 13:

The strength of magnetic field at point P on the axis of short bar magnet is equal to the magnetic induction at point Q on the equatorial line. Find the ratio of the distances from the centre of magnet.

Given: B_axis = B_equator,

To Find: ratio of distances r_P:r_Q = ?

Solution:

Ans: The required ratio of distances is 2^1/3: 1

Example – 14:

Earth’s magnetic field may be imagined to be due to a magnetic dipole located at the centre of the earth. If the magnetic field at a point on the magnetic equator is 3 x 10^-5 Wb/m². What is the magnetic moment of such a magnet? What is the value of earth’s magnetic field at the north pole of the earth? Radius of the earth = 6400 Km.

Given: B = 3 x 10^-5 Wb/m², Point on Equator, distance from centre = r = 6400 km = 6.4 x 10⁶ m

To Find: Magnetic moment = M =? Magnetic field at the north pole =?

Solution:

Ans: The magnetic moment of magnet is 7.86 x 10²² Am²

and magnetic induction at north pole is 6 x 10^-5 T.

Example – 15:

A magnet has magnetic length 0.10 m and pole strength 12 Am. Find the magnitude of the magnetic field B at a point on its axis at a distance of 0.02 m from centre.

Given: Magnetic length = 2l = 0.10 m, l = 0.05 m, pole strength = 12 Am, distance from the centre = r = 0.02 m, μ_o/4π = 10^-7 Wb/Am.

To Find: B_axis =?

Solution:

Ans: Magnetic induction on the axis is 3.4 x 10^-5 T.

Example – 16:

Two short magnets A and B of magnetic moments M₁ = 2.7 Am² and M₂ = 3.2 Am² respectively are kept as shown. Find the resultant magnetic field due to the magnets at P. r₁ = 30 cm and r₂ = 40 cm.

Given: M₁ = 2.7 Am², M₂ = 3.2 Am², r₁ = 30 cm = 0.3 m, and r₂ = 40 cm = 0.4 m.

Science > Physics > Magnetism > Magnetic Induction at a Point on the Axis and the Equator

The post Magnetic Induction at a Point on the Axis and the Equator appeared first on The Fact Factor.

In this article, we shall study types of magnetism, types of magnetic material, and Curie temperature. On the basis of magnetic behaviour magnetic materials are classified into three types: diamagnetic, paramagnetic, and ferromagnetic substances.

Origin of Magnetism:

The origin of magnetism in substances can be explained by considering the circular motion of electrons. The electrons in atoms move in circular orbits around the nucleus which is equivalent to a circular coil carrying current. The orbital motion of electrons gives rise to an orbital magnetic moment.

In addition, the electrons spin about its own axis constituting a spin magnetic moment.  The resultant magnetic moment of an atom is the vector sum of the orbital and spin magnetic moment.

On the basis of magnetic properties, substances are classified into three groups namely diamagnetic, paramagnetic and ferromagnetic.

Diamagnetic substances:

Those substances which are weekly magnetized when placed in an external magnetic field, in a direction opposite to the applied field are called diamagnetic substances. The magnetism exhibited by these substances is called diamagnetism.

Examples: Copper, gold, antimony, bismuth, silver, lead, silicon, mercury, water, air, hydrogen, nitrogen, etc.

Explanation of Diamagnetism:

The orbital motion of electrons gives rise to an orbital magnetic moment. In addition, the electrons spin about its own axis constituting a spin magnetic moment.  The resultant magnetic moment of an atom is the vector sum of the orbital and spin magnetic moment. In an atom, electrons can have clockwise or anticlockwise spin. Similarly, the electrons can revolve around the nucleus in a clockwise or anticlockwise direction.

In diamagnetic substances, the orbital magnetic moments and magnetic moments of atoms are oriented in such a way that the vector sum of the magnetic moment of an atom is zero.

When a diamagnetic substance is placed in an external magnetic field, the induced e.m.f. in each atom increases.  As a result, the speed of electrons revolving in one direction increases and those revolving in opposite direction decreases.  Thus the substance as a whole acquires a net magnetic moment in a direction opposite to the applied field.

Characteristics of Diamagnetic Substances:

• The magnetic moment of every atom is zero.
• They are weakly repelled by an external magnetic field.
• When placed in a non-uniform magnetic field, they tend to move from the stronger to the weaker part of the field.
• In an external magnetic field, they get weakly magnetized in the direction opposite to that of the field
• When a rod of diamagnetic substance is suspended in a uniform magnetic field, it comes to rest with its length perpendicular to the directions of the field.

• For diamagnetic substances magnetic susceptibility is negative.
• In the absence of an external magnetic field, the net magnetic moment of diamagnetic substance is zero.
• On removal of the external magnetic field, diamagnetic substances lose their magnetism.
• If a watch glass containing a small quantity of diamagnetic liquid is placed on two dissimilar magnetic poles, the liquid shows a depression in the middle.

If a magnetic field is applied to a diamagnetic liquid in one arm of U-tube, the liquid level in that arm is lowered.

If diamagnetic gas is introduced between pole pieces of magnet, it spreads at a right angle to the magnetic field.

Paramagnetic Substances:

Those substances which are weekly magnetized when placed in an external magnetic field in the same direction as the applied field are called Paramagnetic substances.  They tend to move from weaker to the stronger part of the field. The magnetism exhibited by these substances is called paramagnetism.

Examples: Aluminium, platinum, manganese, chromium, sodium, calcium, lithium, tungsten, niobium, copper chloride, crown glass, oxygen etc.

Explanation of Paramagnetism:

In paramagnetic substances, the orbital and spin magnetic moments of atoms are oriented in such a way that, each atom has a permanent magnetic dipole moment. However, due to thermal motion (vibration), the direction of the magnetic moments of the atoms have random orientations.  As a result of this, the net magnetic moment of a paramagnetic substance is zero.

When a paramagnetic substance is placed in an external magnetic field, each atomic magnets tend to align in the direction of the field.  Thus a paramagnetic substance acquires a net magnetic moment (magnetization).

However, the degree of alignment depends directly on the strength of the external field and inversely on the temperature of the specimen.

When the paramagnetic’ substance is removed from the magnetic field, the alignment is once again disturbed by thermal vibrations and it gets demagnetized.  For this, reason, paramagnetic substances cannot be used as permanent magnets.

Characteristics of Paramagnetic Substances:

• Every atom is a magnetic dipole having a resultant magnetic moment.
• They are weakly attracted by an external magnetic field.
• When placed in a non-uniform magnetic field, they tend to move from the weaker to the stronger part of the field.
• In an external magnetic field, they get weakly magnetized in the same direction to that of the field
• When a rod of a paramagnetic substance is suspended in a uniform magnetic field, it comes to rest with its length parallel to the directions of the field.
• In absence of an external magnetic field, the magnetic moments of atomic magnets are randomly arranged, hence the net magnetic moment of the paramagnetic substance is zero.
• On removal of the external magnetic field, paramagnetic substances lose their magnetism.
• If a watch glass containing a small quantity of paramagnetic liquid is placed on two dissimilar magnetic poles, the liquid shows an elevation in the middle.

• If a magnetic field is applied to the paramagnetic liquid in one arm of U-tube, the liquid level in that arm rises.

• If paramagnetic gas is introduced between pole pieces of magnet, it spreads in the direction of the magnetic field.
• For paramagnetic substances, magnetic susceptibility is positive and small.
• The susceptibility decreases with an increase in temperature.

Ferromagnetic substances:

Those substances which are strongly magnetized in an external magnetic field in the same direction as the external applied field and retain its magnetic moment even after the removal of the external field are Called Ferromagnetic substances.  They have a very strong tendency to move from weaker to the stronger parts of the external field. The magnetism exhibited by these substances is called ferromagnetism.

Examples: Iron, cobalt, nickel.

Explanation of Ferromagnetism on the Basis of Domain Theory:

Ferromagnetism is a special case of Paramagnetism.  In ferromagnetic substances, to the magnetic dipole moment of atoms, the contribution of the spin magnetic moment is very large.

According to the domain theory, a ferromagnetic substance consists of a large number of small units (regions) known as Domains.  A domain ‘is an extremely small region containing a large number of atomic magnets having magnetic axes aligned in the same direction due to a strong exchange coupling. When a ferromagnetic substance is kept in the magnetic field, the permanent alignment of the domain due to a strong interaction (force) takes place this force is known as exchange coupling. In one domain the magnetic dipole moments of all the atoms are aligned in the same direction. Hence each domain has a resultant magnetic dipole moment.  This permanent alignment is due to a strong interaction (force) known as exchange coupling.

However, in the absence of an external magnetic field, various domains have random orientations and hence their resultant magnetic moment is zero.

When a ferromagnetic substance is subjected to an external magnetic field, each domain experience a torque.  As a result of this, some domains rapidly rotate and remain aligned parallel to the direction of the field. This is called domain rotation or flipping.

At the same time, those domains whose magnetic axes are nearly in line with the external magnetic field grow in size at the cost of the neighbouring domains.  This is called domain growth.

As the strength of the external magnetic field is increased, more and more domains flip and align in the direction of the external magnetic field.  Finally, at a certain stage, practically all domains get aligned in the direction of the field.  This is known as magnetic saturation.  At this stage, a ferromagnetic substance behaves as a permanent magnet and retains its magnetic property (residual magnetism) even if the external magnetic field is removed.

Characteristics of Ferromagnetic Substances:

They are strongly magnetized when placed in an external magnetic field.

• The substances are made up of a large number of small domains. The atomic magnets in one domain are aligned in the same direction due to strong interaction is known as exchange coupling.
• They do not lose magnetism when the external magnetic field is removed.
• When heated above Curie temperature they become paramagnetic.
• They are strongly attracted by external magnetic field.
• When placed in a non-uniform magnetic field, they tend to move from the weaker to the stronger part of the field.
• In an external magnetic field, they get strongly magnetized in the same direction to that of the field
• When a rod of a ferromagnetic substance is suspended in a uniform magnetic field, it comes to rest with its length parallel to the directions of the field.
• In the absence of an external magnetic field, the magnetic moments of domains are randomly arranged, hence the net magnetic moment of a ferromagnetic substance is zero.
• On removal of the external magnetic field, ferromagnetic substances do not lose their magnetism. i.e. they are permanent magnets.
• For ferromagnetic substances, magnetic susceptibility is positive and large.

Distinguishing Between Diamagnetic and Paramagnetic Substances:

Distinguishing Between Ferromagnetic Substances and Diamagnetic Substances

Distinguishing Between Ferromagnetic Substances and Paramagnetic Substances

Effect of Heat on Ferromagnetic Substance or the Concept of Curie Temperature:

It is the temperature required to destroy the alignment of domains and to make a ferromagnetic substance demagnetized. Above Curie temperature. a ferromagnetic substance behaves as paramagnetic.  When a ferromagnetic substance is heated, the exchange coupling between neighbouring atoms becomes loose and ultimately the domain structure gets vanished.

If the heating is continued then at Curie temperature, the exchange coupling disappears and the domain structure is destroyed and hence the substance becomes paramagnetic.

Curie temperature is the characteristic property of the substance. It is different for different materials. e.g.  Fe (1043 K), Ni (631 K), Co (1394 K), Gadolinium (317 K), Fe2O3 (893 K)

Scientific Reasons:

Diamagnetic substances are weakly repelled by a magnet

The magnetic moment of every atom of diamagnetic substance is zero. In an external magnetic field, they get weakly magnetized in the direction opposite to that of the field.

Hence when placed in a non-uniform magnetic field, they tend to move from the stronger to the weaker part of the field. Hence diamagnetic substances are weakly repelled by an external magnetic field.

If a watch glass containing a small quantity of diamagnetic liquid is placed on two dissimilar magnetic poles, the liquid shows a depression in the middle.

When the dissimilar poles are separated by a small distance then the magnetic field is stronger at midway than at the poles. In an external magnetic field, diamagnetic substances get weakly magnetized in the direction opposite to that of the field. Hence when placed in a non-uniform magnetic field, they tend to move from the stronger to the weaker part of the field. Thus the liquid at the centre moves from stronger to weaker section of the field creating a depression at the centre.

If a watch glass containing a small quantity of paramagnetic liquid is placed on two dissimilar magnetic poles, the liquid shows an elevation in the middle.

When the dissimilar poles are separated by a small distance then the magnetic field is stronger at midway than at the poles. In an external magnetic field, paramagnetic substances get weakly magnetized in the same direction to that of the field. Hence when placed in a non-uniform magnetic field, they tend to move from the weaker to the stronger part of the field. Thus the liquid at the edge moves from weaker to a stronger section of the field creating an elevation at the centre.

Paramagnetic substances cannot be used for making permanent magnets.

In the absence of an external magnetic field, the magnetic moments of atomic magnets are randomly arranged, hence the net magnetic moment of the paramagnetic substance is zero. In an external magnetic field, they get weakly magnetized in the same direction to that of the field.

On removal of the external magnetic field, the magnetic moments of atomic magnets again become randomly arranged.  Hence the paramagnetic substances lose their magnetism. Thus paramagnetic substances are temporary magnets. Hence Paramagnetic substances cannot be used for making permanent magnets.

Ferromagnetic substances are used for making permanent magnets.

In the absence of an external magnetic field, the magnetic moments of domains of ferromagnetic substance are randomly arranged, hence the net magnetic moment of a ferromagnetic substance is zero.  In an external magnetic field, they get strongly magnetized in the same direction as that of the field. The domain size increases.

On removal of the external magnetic field, ferromagnetic substances the increased domain structure is maintained and thus ferromagnetic substances do not lose their magnetism. Hence they are used in making permanent magnets.

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Science > Physics > Magnetism > Types of Magnetic Materials

The post Types of Magnetic Materials appeared first on The Fact Factor.

In this article, we shall study the concept of a magnetic field, magnetic lines of force, types of magnetic material.

When a magnetic needle is kept on a wooden table it comes to rest in the north-south direction. If another magnet is kept on a table the needle comes to rest in some other direction such that one of its poles is in the direction towards the nearer pole of the magnet. Thus the property of the space in which the magnetic needle is kept is changed.

The space around a magnet in which the needle of a compass rests in a direction other than geographical north-south direction is called a magnetic field. It is a vector quantity. It has a magnitude as well as direction. The direction of the field at a point is in the direction in which the needle of the compass rests when it is kept at that point.

Magnetic Lines of Force:

The magnetic field can be represented by drawing lines called as magnetic lines of force. A magnetic line of force is defined as a curve drawn in the magnetic field in such a way that the tangent to the curve at any points gives the direction of the field.

Plotting of Magnetic Lines of Force:

Draw a line in the middle of a paper fixed on a drawing board to represent the magnetic axis of the magnet. Place the magnet on the paper such that its magnetic axis coincides with the line drawn on the paper. Mark the outline of the magnet. Keep a small plotting magnetic needle (plotting compass) and place it on paper such that its south pole is directed towards point 0 at the edge of the bar magnet, and mark the point b1 in the direction in which the north pole of the compass points. Repeat the procedure by shifting the compass to a new point such that its south pole is directed towards point 1 to get point 2, 3, 4,…., Draw a smooth curve through all plotted points, which give the magnetic lines of force.

Experiment to Show Nature of Lines Formed Due to Bar Magnet:

Place a magnet below a sheet of stiff paper and spread iron filings on the top of the paper uniformly. Tap the paper gently. We observe that the iron filings arrange themselves along the curved lines as shown.

These lines are called magnetic lines of force and are formed due to induced magnetism in iron filings and aligning in the direction of the field created y the magnet. If the compass needle is placed at any point its needle rests along the magnetic line of force.

Pattern of Magnetic Lines of Force:

Bar Magnet:

Horse Shoe Magnet:

Two Bar Magnet Unlike Poles Facing Each Other:

Two Bar Magnet Like Poles Facing Each Other

Characteristics of Magnetic Lines of Force:

• Magnetic lines of force are imaginary (hypothetical).
• They are closed, continuous curves.
• Magnetic lines of force always emerge or start from the north pole and terminate on the south pole. Inside the magnet, the lines of force move from the south pole to the north pole.
• The lines of force emerged or terminate normally to the surface of the magnet.
• When two dissimilar poles of two magnets are brought near each other the lines of force assist each other hence there is an attraction between two poles.
• When two similar poles of two magnets are brought near each other the lines of force oppose each other and there is repulsion between the two poles.
• The lines of force never intersect each other if they do so it means that there are two directions for the magnetic field at the point of intersection, which is not possible
• Lines of force have a tendency to shirk.
• Lines of force exert lateral pressure on each other.
• The strength of the magnetic field depends on the number of lines per unit area. This quantity is called the intensity of the magnetic field. If the lines of force are crowded together then the magnetic field is strong. We can observe that the lines of force are crowded near the poles, where the magnetic strength of the field is more.
• If the lines of force are equally spaced then the field is uniform.

Types of Magnetic Fields:

• If a magnetic induction has the same magnitude and direction at all the points in the region, then the magnetic field is said to be uniform.
• If a magnetic induction varies in both the magnitude and the direction at all the points in the region, then the magnetic field is said to be nonuniform.
• Earth’s magnetic field may be regarded as a uniform over a small region.

Representation of Magnetic Field:

Uniform Magnetic Field:

Uniform Magnetic Field Perpendicular to Plane of Paper and Coming Out of It:

Uniform Magnetic Field Perpendicular to Plane of Paper and Going into It:

Origin of Magnetism:

The origin of magnetism in substances can be explained by considering the circular motion of electrons. The electrons in atoms move in circular orbits around the nucleus which is equivalent to a circular coil carrying current. The orbital motion of electrons gives rise to an orbital magnetic moment.

In addition, the electrons spin about its own axis constituting a spin magnetic moment.  The resultant magnetic moment of an atom is the vector sum of the orbital and spin magnetic moment.

Types of Magnetic Substances:

Diamagnetic Substances:

Those substances which are weekly magnetized when placed in an external magnetic field, in a direction opposite to the applied field are called diamagnetic substances. They tend to move from stronger to weaker parts of the field. Examples: Copper, Gold, Antimony, Bismuth, Water, Air, Hydrogen, etc.

Paramagnetic Substances:

Those substances which are weekly magnetized when placed in an external magnetic field in the same direction as the applied field are called Paramagnetic substances.  They tend to move from weaker to a stronger part of the field. Examples:  Aluminium, Platinum, Manganese, Crown glass, oxygen, etc.

Ferromagnetic Substances:

Those substances which are strongly magnetized in an external magnetic field in the same direction as the external applied field and retain its magnetic moment even after the removal of the external field are Called Ferromagnetic substances. They have a very strong tendency to move from weaker to the stronger parts of the external field. Examples: Iron, cobalt, nickel

Curie Temperature:

It is the temperature required to destroy the alignment of domains and to make a ferromagnetic substance demagnetized. Above Curie temperature. a ferromagnetic substance behaves as paramagnetic. e.g. Fe (770 °C), Ni (360 °C), Co (1150 °C).

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Science > Physics > Magnetism > Magnetic Field and Magnetic Lines of Force

The post Magnetic Field and Magnetic Lines of Force appeared first on The Fact Factor.

In this article, we shall see the properties of magnet and experiments to verify them

Types of Material:

Magnetic Materials: Materials which are attracted by magnets are called magnetic material. e.g.  Iron, cobalt, nickel

Nonmagnetic Materials: Materials which are not attracted by magnets are called non-magnetic material. e.g. glass, plastic, rubber.

Experimental Verification of Properties of Magnet

Experiment to Find Magnetic Material:

Bring a magnet near the material to be categorized. If the material is getting attracted towards the magnet, then the material is categorized as magnetic material. If the material is not getting attracted towards the magnet, then the material is categorized as nonmagnetic material.

Experiment to Locate Poles of a Magnet:

Suspend a bar magnet with twistless thread to a wooden stand such that it is capable of rotating about a transverse axis passing through its centre. Thus the magnet is horizontal. Let the magnet comes to rest. When it comes to rest, the end pointing towards the geographical north is called the north pole and the end pointing towards the geographical south is called the south pole.

Experiment to Show That the Strength of Magnet is Located at the Poles:

Take some iron filings in a dish. Place a bar magnet in it. We observe that the iron filings stick to the magnet but cluster around the poles rather than the middle portion of the magnet. This shows that the strength of the magnet is located at the poles.

Experiment to Show That the Like Poles Repel and Unlike Poles Attract:

Suspend a bar magnet with twistless thread to a wooden stand such that it is capable of rotating about a transverse axis passing through its centre. Thus the magnet is horizontal. Let the magnet comes to rest. When it comes to rest, the end pointing towards the geographical north is called the north pole and the end pointing towards the geographical south is called the south pole.

Now bring north pole of another magnet near the north pole of the suspended magnet. We observe that the north pole of the suspended magnet moves away from the north pole of the other magnet. This phenomenon is called the magnetic repulsion.

Now take away the other magnet and allow the suspended magnet to come to rest. Now bring south pole of another magnet near the north pole of the suspended magnet. We observe that the north pole of the suspended magnet moves towards the south pole of the other magnet. This phenomenon is called magnetic attraction.

Thus we can conclude that like poles repel and unlike poles attract. In this experiment, if you interchange the poles, the result will be the same.

Note:

If an iron rod is suspended in case of the magnet, then in both the cases the rod will get attracted towards the other magnet. Hence attraction is not a sure test of magnetism.

Experiment to Show That the Poles of Magnet Cannot Be Separated:

Take a thin bar magnet which can be cut by scissors. Mark its north pole and south pole. Cut this magnet into two halves at the centre. Put these pieces in iron filings. Iron filings get attracted to both pieces at the ends.

Suspend these pieces with twistless thread to a wooden stand such that it is capable of rotating about a transverse axis passing through its centre. Thus the magnet is horizontal. We observe that both the pieces come to rest in the north-south direction.

This shows that no matter how small you cut the magnet, each piece will have both the north pole and south pole. Thus the two poles of a magnet cannot be separated from each other.

A horizontally suspended magnet always comes to rest in the north south direction:

The earth itself is a giant magnet. Its magnetic North pole is near geographical South pole. Its magnetic South pole is near geographical North pole.

Now, unlike poles of magnet always attract each other and like poles of magnet always repel each other. Thus the north pole of the suspended magnet gets attracted towards the magnetic south pole of the earth (geographical north). Similarly, the south pole of the suspended magnet gets attracted towards the magnetic north pole of the earth (geographical south).

Thus the magnet when suspended in the air such that it is free to rotate about a transverse axis passing through its centre, it always comes to rest in the north-south direction.

If a bar magnet is suspended vertically, it does not hang in the north-south direction:

When a bar magnet is suspended vertically it is acted upon by two forces. Magnetic force due to earth’s magnetic field and the gravitational force due to earth’s gravitational field.

The magnetic force tries to align the magnet in the north-south direction, while gravitational force tries to move the magnet downward. The gravitational force acting on the magnet is much stronger than the magnetic force acting on the magnet. Hence, a bar magnet when suspended vertically, it does not hang in the north-south direction.

Repulsion rather than attraction is the test for identifying magnet:

Unlike poles of the magnet always attract each other and like poles of the magnet always repel each other. Thus there are two phenomena involved: attraction and repulsion. If there is neither attraction nor repulsion due to bringing a magnet near the material, then the material is nonmagnetic. If it is getting attracted then it may be magnetic or a magnet.

If the material is brought near a north pole of a magnet and is getting attracted. Then there are two possibilities Firstly, the material is magnetic and itself is not a magnet and is getting attracted towards the magnet and secondly, the material is a magnet and its south pole is getting attracted towards the north pole of the magnet.

Now, if a material is brought near a north pole of a magnet and is getting repelled. Then it means that the material is a magnet and its north pole is brought near the north pole of the magnet. Thus, repulsion rather than attraction is the test for identifying magnet.

These properties of magnet are used in different practical applications.

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1.1.1.1 What is Physics?

Science word is derived from the Latin word ‘Scientia’ which means ‘to know’. Science has many disciplines, Physics being one of them. The word Physics is derived from the Greek word ‘Fusis’ meaning ‘nature’. Physics is that branch of Science which deals with the study of matter and energy or matter or motion i.e. Physics is a study of matter and energy in its different forms. In other words, physics is the study of nature and its laws. We expect that all the different events taking place in nature always take place according to some basic rules and revealing these rules of nature from the observed events in physics.

As physics is a study of nature and its behaviour it is real science. No one has been given authority to frame the rules. Sir Issac Newton, Einstein are the great physicist because using the observations available at that time, they could guess and frame the laws of physics, which explain these events and the observations in a convincing way. If a new phenomenon is observed which can not be explained using existing laws or rules we are always free to change the rules.

Knowledge of Physics overlaps with other sciences considerably, hence such overlapping gives rise to subjects like Biophysics, Biochemistry, Astrophysics, Geophysics, etc.

Physics can be conveniently divided into two parts, classical Physics (Pre-1900) and modern Physics (Post – 1900). Classical physics includes the study of mechanics, gravitation, heat, sound, light, electricity and magnetism. Modern Physics includes the study of quantum mechanics, relativity, atoms, molecules, nuclei, elementary particles, and condensed matter.

The complex physical phenomena involving wide range of length, mass. and time can be easily understood due to following reasons:

• A quantitative study of various natural phenomena shows that there is some regularity and symmetry even in the most complex phenomenon which helps us to understand it.
• All these phenomena can be explained in terms of only a few basic laws.
• Complex phenomena can be separated into simpler phenomena and by understanding these simple phenomena, the complex phenomena can be understood.

Scientific Methods:

The study of science and particularly in Physics is based on systematic observation, logical reasoning, model making, and theoretical prediction and necessary modifications. All the four steps taken together constitute what we call the ‘scientific method’. The scientific method helps us to describe the given physical phenomenon or behavior of a physical system in terms of a limited number of laws. This gives us what we call ‘theory’. The theory should be self-consistent and consistent with known experimental data. The discrepancy between the theory and experimental data has to lead to new theories in Physics.

Relation Between Physics and Mathematics:

Physics is directly related to maths because the description of nature becomes easy if we have the freedom to use mathematics. In physics, we use mathematical techniques like algebra, trigonometry, and calculus. Thus mathematics is a language of physics. Without knowledge of mathematics, it would be much more difficult to discover, understand and explain the laws of nature. But we should note that mathematics itself is not physics. To understand nature is a journey of physics, mathematics is the mean of the journey.

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1.1.1.2 Scope of Physics:

The scope of physics is broad and encompasses the study of the fundamental principles governing the natural world. Physics not only explores the properties and behaviour of matter and energy but also plays a crucial role in advancing technology, contributing to other scientific disciplines, and addressing fundamental questions about the nature of the universe. Here are key aspects of the scope of physics:

Mechanics:

Mechanics is a branch of physics, which deals with the motion of material bodies. In this branch, the forces responsible for producing or changing the motion of the body are studied. The energy involved is also studied. Newton’s laws of motion, the law of conservation of momentum and energy, Newton’s gravitation law forms the base of this branch of Physics.

Heat:

Heat is the energy that a body possesses by virtue of the motion of the molecules of which it is composed and the potential energy due to interatomic forces. The term heat is also used to indicate the energy in the process of transfer between an object and its surroundings because a difference exists between their temperatures. Thermodynamics is the name given to the branch of physics which studies the relationship between heat and mechanics.

Acoustics:

Acoustic is a branch which studies sound. Wave motion is studied in this branch.  An object in a state of vibration can set medium particles in the vibration and this disturbance in the medium can travel from one point to another. Thus sound is wave motion itself.

Optics:

Optics is a branch of science which studies electromagnetic waves to which the eye responds (light). Propagation of light means the propagation of electromagnetic waves with varying electric and magnetic fields through a vacuum or a transparent medium. It has two broad branches: geometric optics and physical optics.

Electricity and Magnetism:

These topics are interrelated with each other. We have to take the help of another topic when we are studying one of them individually. Electricity deals with the forces on charged particles, the effect of such forces. It also studies the phenomenon caused by the motion of charged particles. Magnetism can have an effect on the electric current. magnetic materials can be used in producing electric currents. Electronics is the branch of electricity.

Modern Physics:

Modern physics is the branch of physics which deals with the recent developments in the science-related to physics such as Radioactivity, X-Rays, Cathode Rays, Atomic and Molecular Structure, Quantum Theory and wave mechanics, etc.

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1.1.1.3 Pioneers of Physics

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1.1.1.4 Click Here to find the List of Noble Prize Winners in Physics

Conclusion:

Physics is a branch of science that seeks to understand the fundamental principles governing the natural world, encompassing everything from the smallest particles to the largest galaxies. It involves the study of matter, energy, space, and time, as well as the interactions between these elements. Physicists explore the fundamental laws and forces that govern the behaviour of the universe and seek to explain and predict the observed phenomena. Physics relies heavily on mathematical models and experimental observations. The scientific method is a fundamental aspect of physics, involving the formulation of hypotheses, experimentation, and the development of theories that can be tested and refined through further observations and experiments.

Related Topics:

• 1.1.2 Scientific Methods
• 1.1.3 Scientific View
• 1.1.4 Physics and Other Sciences

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