ALPHY6: ELECTROMAGNETISM

This unit explains Electromagnetism

Electromagnetism can be considered as the science of electromagnetic fields. When an electric current passes through a conductor, a circular electromagnetic field is created around it.

The direction of the current decides the direction of rotation of the created magnetic field. The current strength as well as length of the conductor decides the force of electromagnetism developed. Change of the magnetic field can produce electricity.

Magnetic field lines

Magnets create magnetic fields. These magnetic fields cannot be seen. They fill the space around a magnet where the magnetic forces work, and where they can attract or repel magnetic materials.

Finding magnetic fields

Although we cannot see magnetic fields, we can detect them using iron filings. The tiny pieces of iron line up in a magnetic field.

Field lines around a bar magnet

Field lines around a bar magnet

Drawing magnetic field diagrams

It would be difficult to draw the results from the sort of experiment seen in the photograph, so we draw simple magnetic field lines instead.

Diagram of a bar magnet showing magnetic field lines going from the north to the south pole of the magnet.

In the diagram, note that:

  • the field lines have arrows on them
  • the field lines come out of N (north pole) and go into S (south pole)
  • the field lines are more concentrated at the poles

The magnetic field is strongest at the poles, where the field lines are most concentrated.

Two bar magnets

The magnetic field pattern when two magnets are used is shown in this diagram.

Diagram showing the magnetic field lines of a single bar magnet, two unlike poles attracting, and two like poles repelling.Magnetic field lines for fields involving two magnets

Note the different patterns seen when two like poles are used and two opposing poles are used.

Uniform magnetic field

When magnetic field lines are the same distance apart from each other, we say that the magnetic field is uniform.

This is shown in the diagram below.

Diagram showing the magnetic field lines in an uniform field.Magnetic field lines in a uniform fieldELECTROMAGNETISM ASSIGNMENT

Electromagnetism has two meanings, depending on whether viewed at the subatomic level or on an everyday scale.

At the subatomic level, electromagnetism is defined as the force between electrically charged particles. It is considered one of the fundamental interactions of matter. Oscillating electrical charges result in electromagnetic waves.

On a larger scale, electromagnetism is the creation of a magnetic field from the movement of electrical charges. It usually concerns the use of electric current to make electromagnets, which is called electrodynamics. Another effect is electromagnetic induction, which is using an electromagnet or changing magnetic field to induce an electric current.

Electromagnetism at the subatomic level

At the subatomic level, electromagnetism is related to the electromagnetic force that causes the attraction and repulsion of electrically charged particles. It is considered one of the fundamental forces in nature, that also includes gravitational and nuclear forces.

When electrically charged particles, such as electrons, are put into motion, they create a magnetic field. When these particles are made to oscillate, they create electromagnetic radiation. This can include radio waves, visible light, or x-rays, depending on the frequency of the oscillation.

Electrodynamics

Electrodynamics is creating a magnetic field from an electric current.

When electricity passed through a wire, a magnetic field is created around the wire. Looping the wire increases the magnetic field. Adding an iron core greatly increases the effect and creates an electromagnet. You can also create an electromagnet without the iron core. That is usually called a solenoid.

Magnetic field created from flowing electrons

When DC electricity is passed through a wire, a magnetic field rotates around the wire in a specific direction.

Magnetic field rotating around wire

Magnetic field rotating around wire

Right hand rule

To find the direction the magnetic field is going, you can use the “right-hand rule” to determine it. If you take your right hand and wrap it around the wire, with your thumb pointing in the direction of the electrical current (positive to negative), then your fingers are pointing in the direction of the magnetic field around the wire. Try it with the picture above.

You can also see the direction of the magnetic field by placing a compass near the wire.

Wire in a coil

Wrapping the wire in a coil concentrates and increases the magnetic field, because the additive effect of each turn of the wire.

Coiled wire increases magnetic field

Coiled wire increases magnetic field

A coil of wire used to create a magnetic field is called a solenoid.

Electromagnet

Wrapping the wire around an iron core greatly increases the magnetic field. If you put a nail in the coil in the drawing above, it would result in an electromagnet with the a north seeking pole on the “N” side.

Electromagnetic induction

Electromagnetic induction is creating an electric current from a changing magnetic field.

When a wire moves through a magnetic field, the electromagnetic effect takes place, creating an electric current through the wire.

Current created in wire moving through magnetic field

Current created in wire moving through magnetic field

In 1820, a Danish scientist named Hans Oersted discovered that a magnetic compass could be deflected from its resting position if a wire carrying electric current were placed near the compass. This deflection of the compass only occurred when current was flowing in the wire. When current was stopped, the compass returned to its resting position.

Magnetic Field

This graphic seems to indicate that any wire in which an electric current is flowing is surrounded by an invisible force field called a magnetic field. For this reason, any time we deal with current flowing in a circuit, we must also consider the effects of this magnetic field. We have all probably had experiences with magnets at one time or another. Magnets attract certain types of material like iron but almost nothing else.

Electromagnetism

The term electromagnetism is defined as the production of a magnetic field by current flowing in a conductor. We will need to understand electromagnetism in greater detail to understand how it can be used to do work.

Coiling a current-carrying conductor around a core material that can be easily magnetized, such as iron, can form an electromagnet. The magnetic field will be concentrated in the core. This arrangement is called a solenoid. The more turns we wrap on this core, the stronger the electromagnet and the stronger the magnetic lines of force become.

ASSIGNMENT : ELECTROMAGNETISM ASSIGNMENT MARKS : 10  DURATION : 1 week, 3 days

 

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