Photo Electric Effect

The emission of electrons from the surface of metal when a beam of light with sufficiencly high frequency incident on it is called as photoelectric effect. Lenard studied the photo electric photometric phenomena in 1900 A.D its process and resuits described . It consists of an evacuated tube containing two electrodes and a window through light can be enter and incident on one electrodes varying potetial differnce can be applied between two electrodes by help ofrheostat and sheel. Beam of light of various frequency and intenties are allowed to incident an electrode on electrode and the enjection of electode is obserbed by nothing current in ammeter. 

LENARD FOUND THE THREE RESULTS BE WHICH ARE GIVEN BELOW:

1. Photometric effect occurs only when light of sufficient frequency whose value depends on nature of metal surface , incident on metal surface. The minimum frequency for which photometric effect frequewncy of metal surface.
2. The number of photoelectrons emitting per second depends on the intencity of incident light doesnot depends on frequency of incident light.
3. The kinetic energy of photoelectrons emitted from metal surface depends on the frequency of incident on intensity of incident light .

CAPACITOR

A capacitor is a device or arrangement used to increase the capacitance of a conductor without increasing the size of the conductor but bringing another earthen conductor near it. Two conductors separated by an insulated material used to separated by an insulated capacitor. The insulated material used to separate the metal plates is called the dielectric material or in short dialectic.For example:two parallel metal plates separated by mica forms capacitor . charged cloud and earth's surface separated by air forms a capacitors,
FORMATION OF CAPACITOR :Supposed two metal A and B is arranged as shown, the arrange segment is made to increase the capacitance of the conductor . A without changing the size of the conductor of a capacitor . Let us supposed A and B is separated by an insulated dielectric material. The arrangement will increase the capacitance of the metal plate A. The second plate B is always earthen.It can be shown as given below.
When the conductor B is kept near a positively charged conductor A then it induces opposite charges inside the plate B as shown.Similarly induce similar positive charge on outside B will be neutralized by the charges from the earth. The induced negative charge inside the plate B decreases the amount of force to be applied to carry an unit positive charge from infinity to the plate that plate A is the electrical potential v of the plate. Hence charged . As the potential decreases the capacitance c = q/v must be increased .
Thus the presence of the earthen metal plate B near the conductor A increases the capacitance of the metal plate A. The metal plate A and B forms an electric device called the capacitor .
The function of such formed capacitor is to increase the capacitance of the capacitor so as possible to store charges on them.

Thus every capacitor contains two conductors one charged, other earthen and separated by an insulator known as dielectric, thus formed capacitors are used to store the electric charged.

X-RAY

X-RAY:Electromagnetic radiation having wavelength ranged from 0.1 arm strong to 100 arm strong are called x-ray.It consists of an evacuated round tube containing a tungsten filament at one end connected with 9v (10w tension) battery . As electric current flows along filament, it gets heated and then electron evaporates from its surface.Electrons beam is collocated by the help slit placed near it. These electrons are accelerated by keeping a target made of high atomic weight element at positive potential with respect to filament,when accelerated(i.e energetic) electrons strike tungsten target, few electrons staying at the lower energy level in tungsten atom are knocked out and then vacancies created are filled up with the transition of electron from higher energy level giving the emission of electromagnetic radiation.These emissions are x-rays.Maximum energy of a photon of x-rays produced is equal to the maximum energy of striking electron.
i.e 1/2mv^2 = ev =hf maximum
therefore f maximum= ev/h
Hence,the frequency of x-rays emitted depend on the potential difference applied between filament and target used . The number of increased by increasing the filament current.
Only a fraction of electron beam energy is used up in the production of x-rays and the large part of electron beam energy is converted in producing heated Target. A water cooling arrangement is provided to exchange heat from target.
PROPERTIES OF X-RAYS:

1. They are electromagnetic Waves with wavelength from 0.1 to 100 arm strong.
2. They travel with 3*10^8m/s velocity in vac cum in straight line.
3. They are uncharged rays and so not deflected by electric and magnetic field.
4. They can ionise the gas through soft substance like paper,flesh,wood etc but cannot pass through hard substance like steel sheet and bone.
5. They can affect photographic plate i.e. they have reducing action on silver halide compound.
6. They show fluoresce effect on the substance like zinc sulphide and barium platino cynide.
7. They are diffracted when pass through thin sheet of crystal.

USES OF X-RAYS
They are used in various fields as given below:

1. Medical use : Physitotheraphy (a) They are used to cure malignant skin disease by exposing skin to x-ray beam.(b)Surgery: They are used to detect the disorders in certain internal organ, presence of hard substance in internal organ and fracture of bone.
2. Industry and engineering: They are used to detect the presence of air bubbles and cracks in valuable finished product in factory.
3. Investigation: They are used to detect the presence of arms explosive and opium inside large packets.
4. Scientific research : They are used to know the crystal structure of substance and to measure the inter atomic distance in crystal.

X-RAY DIFFRACTION
IN 1912A.D van lau found that x-rays are diffracted when a narrow beam of x-rays incident on thin sheet of zinc sulphide. The spot produced on photographic plate after emerging from thin sheet of zns was arranged in regular way. It was concluded that atoms must be arranged in regular pattern in zns sheet and diffraction occurs because the space between two atoms act as slit having dimension in the range of wave length of x-rays used.