Atom Bomb

        The working principle of atom bomb is nuclear fission. Here an uncontrolled fission reaction takes place. When the bomb explodes large quantity of energy in the form of heat, light and radiation is released, a temperature of millions of degrees and pressure of millions of atmosphere are produced. Human life is impossible under such explosion. These bombs were used in World War II and were exploded over Hiroshima and Nagasaki in Japan.

Principle

 

        The splitting of atomic nuclei release enourmous energy. When a single free neutron strikes the nucleus of an atom of fissile material like U^235 and Pu^239, It usually knocks two or three more neutrons free energy is released when those neutrons split off from the nucleus,and newly released neutrons strilce other U^235(or Pu^239) Nuclei, splitting them in a same way,releasing more energy and more neutrons.This process is occur in the atomic bomb.

Nuclear Reactor

          In nuclear fission, a very large amount of nuclear energy is liberated within an extremely small interval of time. Consequently, it is not possible to convert the nuclear energy for any useful purpose. So, a device becomes necessary to control the reaction in nuclear fission. Such a device is called nuclear reactor.

         The nuclear energy from nuclear fission has many uses. A nuclear power plant produces electric power from the nuclear energy of nuclear of nuclear fission.

         A Nuclear reactor is a device in which nuclear chain reactions are initiated, controlled and sustained at a steady rate.

       A Nuclear reactor is used to convert nuclear energy into heat and electrical energy.

The Production Of Nuclear Energy

     

      A nucleus makes up most of the mass of every atom. This nucleus is held together by an extremely powerful force called nuclear force. Because of this force, a large amount of energy is concentrated in the nucleus. 

       Any process in which a particle penetrates a nucleus and changes it to produce nuclear energy is called nuclear reaction. In nuclear reaction, nuclear energy is produced by two processes namely nuclear fission and fusion. 

Nuclear Fission

The process of breaking up of the nucleus of a heavy atom into two or more smaller nuclei with the release of a large amount of energy is known as nuclear fission.

           ( or )

Nuclear fission is a nuclear reaction in which nucleus of a heavy atom splits into smaller atoms(parts)with lot amount of energy.

The energy produced is known as nuclear energy, because of the original mass of the sum of the masses of the products produced after nuclear fission. The difference between these masses before and after the nuclear fission is converted into nuclear energy.  

Nuclear Fusion

Nuclear fusion is a process in which two or more light nuclei combine to form a heavy nucleus. The difference in mass is converted into energy. The energy liberated is called thermo-nuclear energy. For example, the energy production in the sun and stars is due to the nuclear fusion. In sun, four hydrogen nuclei combine to form a helium nucleus at very high pressure and temperature. Also, hydrogen bomb works by the principle of nucleus fusion. It is more powerful than an atom bomb.

Nuclear fusion produces s more energy than nuclear fission, but nuclear fusion requires certain energy surrounding to happen.

NUCLEAR ENERGY

      Nuclear energy results from the changes occurring in the nucleus of atoms. Scientists and Engineers have found many uses for the nuclear energy, especially in producing electricity.
       Nuclear energy provides 16% of world's electricity.Nuclear energy is produced naturally(sun and star's energy)and may made operations under human controll(Nuclear reactors).

Electric Bell

Construction

           The electric bell consists of an electromagnet. In front of the electromagnetic poles, there is a soft iron piece. The soft iron piece is attached to the vibrator. Vibrator is a rigid metallic strip having a hammer at its free end. The gong is fixed against the hammer. Also, platinum strip is fixed to the vibrator. By adjusting screw in contact-maker, contact is made with a platinum strip at a point. This point is called contact point. 

Working

               When key is pressed, the electric circuit is completed and the current flows through the electromagnet The electromagnet becomes magnetized and attracts the soft iron piece. When the soft iron piece is attracted, the hammer strikes the gong. The gong produces the sound. This movements breaks the circuit at the contact point between the screw and platinum strip, so that the current stops flowing. The electromagnet gets demagnetized and thereby the soft iron piece is released. The soft iron piece falls back to the original position and makes contact with the screw. The electric circuit is completed again. The above process keeps on repeating. Therefore the soft iron piece keeps on vibrating and giving rise to the continuous ringing of the bell. Electric bells are used as door bells and buzzers.

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.

Camera

        

         The Camera consists of a convex lens supported at one end of a light proof box and a light sensitive film at the other end. The distance between the lens and the film can be adjusted. There is a shutter behind the lens.

            When we click our Camera, the shutter opens and the light from the object passes through the lens. The lens forms a real, diminished and inverted image on the film. A diaphragm of Variable aperture is also provided so that the amount of light entering the Camera can be controlled.