TLE Basic Electronics

Magnetism

Electricity and magnetism are inseparable. To understand electricity means to understand the relationship that exists between magnetism and electricity.

Electric current always produces some form of magnetism, and magnetism is the most common method for generating electricity. In addition, electricity behaves in specific ways under the influence of magnetism.

What you are expected to learn

At the end of this module, you should be able to:

Identify three types of magnets.
Describe the basic shapes of magnets.
Describe the differences between permanent magnets and temporary magnets.
Describe how the earth functions as a magnet.
State the laws of magnetism.
Explain magnetism based on the theory of atoms and electron spin.
Explain magnetism based on the domain theory.
Identify flux lines and their significance.
Define permeability.
Describe the magnetic effects of current flowing through a conductor.
Describe the principle of an electromagnet.
Describe how to determine the polarity of an electromagnet using the lefthand rule.
Define magnetic induction.
Define retentivity and residual magnetism.
Define a magnetic shield.
Describe how magnetism is used to generate electricity.
State the basic law of electromagnetism.
Describe how the left-hand rule for generators can be used to determine the polarity of induced voltage.
Describe how AC and DC generators convert mechanical energy into electrical energy.
Describe how a relay operates as an electromechanical switch.
Discuss the similarities between a doorbell and a relay.
Discuss the similarities between a solenoid and a relay.
Describe how a magnetic phonograph cartridge works.
Describe how a loudspeaker operates.
Describe how information can be stored and retrieved using magnetic recording.
Describe how a DC motor operates.

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some

tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

• The word magnet is derived from the name of magnetite, a mineral that is a natural magnet.

• A magnet can be created by rubbing a piece of soft iron with another magnet.

• An electromagnet is created by current flowing in a coil of wire.

• Horseshoe, bar, rectangular, and ring are the most common shapes of magnets.

• Unlike poles attract and like poles repel.

• One theory of magnetism is based on the spin of electrons as they orbit around an atom.

• Another theory of magnetism is based on the alignment of domains.

• Flux lines are invisible lines of force surrounding a magnet.

Flux lines form the smallest loop possible.
Permeability is the ability of a material to accept magnetic lines of force.
A magnetic field surrounds a wire when current flows through it.
The direction of the flux lines around a wire can be determined by grasping the wire with the left hand, with the thumb pointing in the direction of current flow.
The fingers then point in the direction of the flux lines.
If two current-carrying wires are placed next to each other, with current flowing in the same direction, their magnetic fields combine.
The strength of an electromagnet is directly proportional to the number of turns in the coil and the amount of current flowing through the coil.
The polarity of an electromagnet is determined by grasping the coil with the left hand with the fingers in the direction of current flow. The thumb then points toward the north pole.
Retentivity is the ability of a material to retain a magnetic field.

Electromagnetism

Electromagnetic induction occurs when a conductor passes through a magnetic field.
Faraday’s law: Induced voltage is directly proportional to the rate at which the conductor cuts the magnetic lines of force.

The left-hand rule for generators can be used to determine the direction of induced voltage.

AC and DC generators convert mechanical energy into electrical energy.

A relay is an electromechanical switch.

Electromagnetic principles are applied in the design and manufacture of doorbells, solenoids, phonograph pickups, loudspeakers, and magnetic recordings.
DC motors and meters use the same principles.
Electron beams can be deflected by an electromagnetic field to produce images on television, radar, and oscilloscope screens.

Simulation Activities

Laboratory Experiment

Important Terms

Degaussing a method of demagnetizing a material by using an alternating current. The method involves magnetizing and demagnetizing a material with a diminishing magnetic field until the material has practically zero residual induction.
Diamagnetic a classification of materials that become weakly magnetized but in the direction opposite to the magnetizing field. Diamagnetic materials have a permeability less than 1. Examples include antimony, bismuth, copper, gold, mercury, silver, and zinc.
Electromagnet a magnet that requires an electric current fl owing in the turns of a coil to create a magnetic field. With no current in the coil, there is no magnetic field.
Faraday’s law a law for determining the amount of induced voltage in a conductor.
Ferrite a nonmetallic material that has the ferromagnetic properties of iron.
Ferromagnetic a classification of materials that become strongly magnetized in the same direction as the magnetizing field. Ferromagnetic materials have high values of permeability in the range of 50 to 5000 or even higher. Examples include iron, steel, nickel, and cobalt.
Induction the electric or magnetic effect of one body on another without any physical contact between them.
Left-hand rule if a coil is grasped with the fingers of the left hand curled around the coil in the direction of electron fl ow, the thumb points to the north pole of the coil.
Lenz’s law Lenz’s law states that the direction of the induced current in a conductor must be such that its own magnetic field will oppose the action that produced the induced current.
Magnetic flux ( ) another name used to describe magnetic field lines.
Maxwell (Mx) the cgs unit of magnetic flux. 1 Mx=1 magnetic field line.
Permanent magnet a hard magnetic material such as cobalt steel that is magnetized by induction in the manufacturing process. A permanent magnet retains its magnetic properties indefinitely as long as it is not subjected to very high temperatures, physical shock, or a strong demagnetizing field.
Toroid an electromagnet wound in the form of a doughnut. It has no magnetic poles and the maximum strength of the magnetic field is concentrated in its iron core.