Subject: 

PHYSICS

[mediator_tech]

Term:

FIRST TERM

Week:

WEEK 5

Class:

SS 3

Topic:

MAGNETIC FIELDS

CONTENT

1. The Concept of Magnetic Field:
2. Properties of Magnetic Lines of Force
3. Magnetic Field Patterns
4. Magnetic Field in a Straight Current-Carrying Conductor
5. Magnetic Field Due to Current in a Solenoid
6. Magnets and Magnetization
7. Properties of Bar Magnets
8. Methods of Making Magnets
9. Demagnetization
10. Applications of Electromagnets
11. Temporary and Permanent Magnets
12. The Earth’s Magnetic Field
13. The Angle of Dip
14. Force on a Moving Charge in a Magnetic Field

Magnetic Force on a Current Carrying Wire

And more…

Magnetic fields are one of the most fundamental concepts in physics, and describe the interactions between moving charges or currents. They are characterized by lines of force that represent the direction and magnitude of the magnetic field at any point in space. Properties such as strength and direction can vary depending on a range of factors, including the current-carrying capacity of the wire, nearby magnetic materials and solenoid configurations.

Magnetic field patterns are typically described according to their shape and orientation, such as circular or elliptical. They can also vary in strength depending on the distance from the source or conductor. Some common applications of magnetic fields include electromagnets, solenoids, and the Earth’s own magnetic field.

One of the most basic properties of magnets is their ability to attract or repel certain materials, depending on their polarity. Bar magnets are typically made by aligning tiny magnetic domains in a piece of iron or steel. The strength and direction of this magnetic field can also be manipulated through a range of methods, such as the application of a magnetizing force or by demagnetization.

There are many other applications for magnetic fields in science and technology. Electromagnets are used in a wide range of devices, including motors, generators, and loudspeakers. Permanent magnets are commonly used in products such as refrigerator magnets, industrial lifting magnets, and compasses. And the Earth’s magnetic field is fundamental to many navigation systems, including the use of a compass to determine location.

Despite its importance in physics and technology, the concept of magnetic fields is still not fully understood. Scientists continue to study and research this fascinating phenomenon, with the hope of gaining further insight into its properties and applications.​

The Concept of Magnetic Field:

A magnetic field is an area of influence created by the flow of electric current. It has powerful effects on matter and can be used for a variety of purposes, from powering machines to manipulating materials. A magnetic field can vary in strength depending on its source, and can be manipulated through different methods such as electromagnets or permanent magnets.

Properties of Magnetic Lines of Force

:

The properties of a magnetic field can vary depending on factors such as the strength and orientation of the current-carrying wire, or the configuration of nearby magnetic materials. These lines of force are typically visualized as loops or curves that indicate the direction and magnitude of the magnetic field at any given point in space

(i) They originate from the N-pole and end in the S-pole. ii. Two magnetic lines of force do not cross each other.

(ii) Where the lines of force are close together, the intensity of the field is greater; where they are widely separated, the intensity is less and where they are parallel, the intensity is uniform.

Magnetic field intensity at a point in a magnetic field is defined as the force experienced per unit N -pole placed at that point.

Magnetic potential at a point is the work done in moving a unit N-pole from infinity to that point.

Magnetic Field Patterns

:

Magnetic field patterns can take many different forms and shapes, depending on the source or conductor that is generating them. Some common examples include circular, elliptical, and linear magnetic field patterns, which are typically associated with magnets, electromagnets, and solenoids respectively. The strength of a magnetic field can also vary depending on its distance from the source or conductor, and can be manipulated through a range of techniques.

One of the most basic properties of magnets is their ability to interact with certain materials based on their polarity. For example, bar magnets are typically made by aligning tiny magnetic domains in a piece of iron or steel. The strength and direction of this magnetic field can also be manipulated through a range of methods, such as the application of a magnetizing force or by demagnetization.

EVALUATION

1. What is a magnetic field?
2. Enumerate three properties of magnetic flux.
3. Define a neutral point.

Magnets and Magnetisation

A magnet is a piece of material that can attract iron and other ferromagnetic material.

Generators used in production of electrical power all depends on powerful and efficient magnets and magnetic materials.

Properties of Bar Magnets

Properties of bar magnets include:

1. Direction:When a magnet is freely suspended, it comes to rest in the South-North direction of the earth.
2. Attraction: A magnet has the ability to attract magnetic materials e.g, steel, iron, etc.
3. Force:A magnet exerts force on other magnets in such a manner that like poles repel and unlike poles attract.
4. The inseparable nature of poles on the magnetic dipoles: If a magnet is broken into small pieces, however small it may be, it will still have a North and South Poles. The smallest bit of a magnet is adipole.
5. Magnetic lines of force originate from the North pole and terminate at the South pole.

Magnetic lines of force do not cross each other.

Where magnetic lines of force are close together, the magnitude or intensity of the field is stronger; where they are widely separated it is weaker and when they are parallel, the intensity will be uniform or constant.

The strength of a magnetic field can be measured in units called teslas (T) or gauss (G).

Magnetic fields can be manipulated using a range of techniques, including the application of an external force to change its alignment, or by changing the permeability and/or susceptibility of nearby materials.

One key property of magnetic field patterns is their ability to interact with certain types of materials based on their polarity. For example, a bar magnet is typically made by aligning tiny magnetic domains within a piece of iron or steel. The strength and direction of this magnetic field can be manipulated through various techniques, such as applying an external force to change its alignment, or changing the permeability of nearby materials. Other common examples include circular, elliptical, and linear magnetic field patterns, which are typically associated with magnets, electromagnets, and solenoids respectively.

Methods of Making Magnets

1. Electrical Method:

The best method of making magnets is to use the magnetic effect of an electric current. The material, a steel bar X to be magnetized is placed inside a solenoid; then, the current is switched on for a few seconds and then switched off. When the bar is tested, it is found to be a magnet.

2. Single Touch:

The material X to be magnetized is placed on a table(bench). The pole of a magnet Yis then dragged alone X from one end to the other and lifted well away. It is brought back again to X at the far end and the process is repeated several times.

3. Divided or Double Touch:

The material X is stroked repeatedly in opposite direction by the opposite poles of the two bar magnets A and B. The stroking begins in the middle of X each time.

4. Hammering in the Earth’s Field:

A weak magnet could be made by using the influence of the earth’s magnetic field. This field acts at an angle to the horizontal called the ‘’angle of Dip’’. It varies from place to place. It is about 70° in England and Britain. If it is done in the N-hemisphere, the lower end will be N and same with S-hemisphere.

Demagnetisation

This is the process of making a magnet to lose its magnetic properties. It is the removal of the ferromagnetic properties of a body by disordering the domain structure of that body. Methods of demagnetization include:

1. Hammering: magnets can be partially demagnetized by hammering them hard when they are pointing East-West, that is0, at 90° to the earth’s magnetic field direction.
2. Heating: They can also be partially demagnetized by heating them strongly.
3. Electrical method: This is the best method of demagnetization. Here, alternating current is used. The bar magnet to be demagnetized is placed inside the solenoid with its axis pointing east-west. A rheostat is added to adjust the current’s value. The a.c is switched on and after a few seconds, the bar is slowly withdrawn from the solenoid to a far distance away.

Applications of Electromagnets

An electromagnet is made up of a soft iron core around which an insulated wire is wound. It becomes a magnet only when current flows in the wire. It is a temporary magnet and all temporary magnets are made of soft iron core.

The strength of electromagnets increases with:

1. Increase in the current within the coil;
2. Increase in the number of turns of wire of the coil;
3. Decrease in distance between the poles of the magnet.

The applications/uses include:

1. Electromagnets are used in cranes to lift up heavy loads and objects made of magnetic materials like iron.
2. They are used in making electric devices like electric bell, magnetic relay, switches, telephones earpiece, etc.

 

Temporary and Permanent Magnets

1. A temporary magnet is made up of soft iron core while a permanent magnet is made of strong iron.
2. A temporary magnet only becomes a magnet when current flows through it; but a permanent magnet still maintains its magnetic alignment structure even when there is no flow of current.

S/N

Temporary Magnet

Permanent Magnet

1

Made from soft iron, mu-metal

Made from steel, ticomal,

alicomax, cobalt, nickel

2

Can be easily magnetized

Cannot be easily magnetized

3

Can be easily demagnetized

Cannot be easily demagnetized

EVALUATION      

1. What is demagnetization?
2. State the uses of electromagnets.
3. Mention the various ways of making magnets.

1. Demagnetization is the process of removing or reducing a magnet’s magnetic properties. It is commonly used in applications where high strength magnets are not required, such as in electric devices like relays and switches.
2. Electromagnets are widely used in many applications due to their ability to produce strong magnetic fields with relatively low
3. The main uses of electromagnets include lifting heavy objects in cranes and making electric devices like switches, relays, telephones, earpieces, etc. This is accomplished through various methods such as heating or hammering the magnet when it is pointing east-west at 90 degrees to the earth’s magnetic field direction.
4. There are several different methods for making magnets, including using soft iron cores and steel alloys like cobalt, nickel, and ticomal. Some methods involve heating the magnet or applying a strong electric current to the material to produce magnetic effects. Another method involves hammering an east-west oriented magnet in order to partially demagnetize

GENERAL EVALUATION

1. List two applications of electromagnets.
2. How can the strength of electromagnets be enhanced?
3. Itemize the various ways of making magnets