Uses of Electromagnets

• Electromagnet is an essential part of electric generators, motors, telegraph instruments, loudspeakers, earphones and telephone receivers.
• Electromagnets are also used in electric bells and tape recorders,VCR's Hard disk and Magnetic locks.
• Electromagnets attached to cranes are used to lift huge loads.
• Electromagnets are used for making new magnets or remagnetising the old ones.
• Electromagnets are used to seperate the magnteic materials from non- magnetic materials.

Electromagnets

 

An electro magnet is a type of magnet in which the magnetic field is redused by the flow of the electric current.

The piece of soft iron nail is placed inside a circular coil. Here, soft iron nail is called core. When current is passed through the coil, the soft iron filings are brought near the soft iron nail, then the iron filling cling to the nail. On the other hand, the soft iron nail is demagnetised, when the current is stopped in the coil. This arrangement is called an electromagnet. The electromagnet is thus a temporary magnet. The strength of electromagnet will depend on,

1. Number of turns in the coil
2. The strength of the current
3. The nature of core material.

Electricity

        The term "electricity" comes from the Greek word “electron,” which means, "amber". A Greek philosopher, Thales, noticed that a rubbed a piece of amber with a woolen cloth. As a result of friction, the amber acquired the property of attracting small particles of dust etc.. In other words, the amber becomes charged or electrified. 

 

There are two kinds charges namely, Positive and negative.

Electromagnets   

 

Uses Of Electromagnet 

 

The Electric Bell

MAGNETISM

 

         A mineral discovered in the town of magnesia was found to have a strange property. It could attract pieces of iron towards it. This mineral is named Magnetite after the place where it was discovered. Later, it was found that magnetite is mainly composed of oxides of iron (Fe3O4 ). These are now known as Magnets. The study of magnetic properties is called Magnetism.

Comparison Between The Human Eye And The Camera

Similarities

The Eye	The Camera
1.A real and inverted image is Formed on the retina. 2.The iris controls the amount of light entering the eye. 3.The time of exposure of light is controlled by the eye lids	1.A real and inverted image is formed on the photographic film.   2.The diaphragm controls the amount of light 3.The time of exposure of light is controlled by the shutter.

Differences

The Eye	The Camera
1.The focal length of the eye lens can be changed by the action of ciliary's muscles 2.The retina retains the image only for a short time. 3. The convex lens of the eye is made of a transparent and flexible substance.	1.The focal length of the lens cannot be changed 2.The film retains the image of the object Permanently. 3.The convex lens is made of a glass.

The Defects Of The Eye

The two common defects of the eye are as follows.

1.Short Sight or Myopia

“The person having the short sight can see only the nearer object.” The eyeball of the person having short sightedness is longer than the normal sighted eye. When a parallel beam of light from the distant object is incident on the eye, the rays are brought to focus in front of the retina. Hence the image is not formed on the retina.

A concave lens of suitable focus length can rectify this defect. 2.Long Sight or Hypermetropia

 

          “The person having the long sight can see only the distant object.” The eyeball of the person having long sightedness is shorter than the normal sighted eye. When the light from the nearer subject is incident on the eye, the rays are focused behind the retina. Hence, the image is not formed on the retina.  

A convex lens of suitable focal length can rectify this defect.

 

 

Perception Of Sight

Light from the object is refracted by the cornea through the aqueous humour, iris and pupil onto the eye lens. The eye lens focuses the image through the vitreous humour onto the retina. These images are received by the light sensitive cells of the retina and they transmit the impulses to the brain through the optic nerves.


The ciliary muscles change the shape of the lens and adjust the focal length according to the distance of the objects. Normally the focal length of the eye lens will be about 2.5cm.