DUAL NATURE OF MATTER
Matter has two natures-the particle nature and the wave nature.Let us learn more about them…….
1.THE PARTICLE NATURE OF MATTER……
The particle nature of matter means the nature due to which it is suggested that matter exists in the form of particles..i.e. photons…the main evidence of the particle nature of matter comes from two facts-the photoelectric effect of world renowned physicist albert Einstein and the scintillation effect…..
The photoelectric effect
This experiment was performed by albert Einstein in September 1905..in the experimental setup ,einstein allowed beam of photons to fall on the cathode part of a vacuum tube..he observed that until a certain frequency was reached,the electrons frm the cathode side were not ejected..this frequency he termed as the threshold frequency and the ejected electrons he termed as the photoelectrons…..the photoelectrons were made to travel to the anode side and hence became sources of current from which electrical energy could be generated..the equation relating frequency of photoelectrons and energy is called einstein’s photoelectric equation:-
Here K(max.) means the maximum kinetic energy with which the photoelectrons come out of the metal and W stands for the work function..i.e. the work needed to make the electrons come out…
Here E=h(v-v0)..where h is called planck’s constant..named after the famous german scientist max planck who did pioneering research in this field..Its a fundamental constant of nature whose value is 6.636 * 10^-34 Js….v0 is the threshold or minimum frequency for photoelectric effect to take place…
THE SCINTILLATION EFFECT
In the scintillation effect,alpha,beta and gamma particles are ejected from a vacuum tube and with the help of particle deflectors are made to fall on a flouroscent screen…scintillations or random bright and dark spots are produced on the screen as a result of this..the whole experiment is viewed with the help of a microscope placed few centimeters away..
The two experiments described above prove the particle nature of matter…lets now move on to the wave nature of matter and the related experiments..
2. THE WAVE NATURE OF MATTER……
Matter also has wave like features.it is elaboratively illustrated by young’s double slit experiment..this experiment which establishes the wave like behaviour of light waves can also be extended to matter waves.
YOUNG’S DOUBLE SLIT EXPERIMENT………….
In the experimental set up,two slits are placed about 1mm apart and a screen is placed at a distance of 1 m from the slits..a source of light is kept behind the slits from where light travels in between the slits and falls on the screen.alternate bright and dark bands are produced on the screen.They are equally spaced and are called fringes.the point equidistant from the two slits where light falls is called the central fringe.the intensity of light falling on central fringe is twice the intensity of light falling on its either two sides.the fringe width formula is :-
Beta= lambda D/a..where lambda is the wavelength of light used,D is the distance of the screen from the slits and a is the aperture length…these dark and light bands thus prove the fact that light as well as matter have wave like properties because they are not like the particle nature of light which suggests that only uniform band should form..
EINSTEIN’S MASS ENERGY EQUIVALENCE RELATION……..
Here m is the rest mass of photons and c is the velocity of light..this equation is valid only for photons since other elementary particles have non-zero rest mass.now,two things are to be kept in mind here..one is the difference between rest mass and moving mass..rest mass is the mass which a particle has when it is at rest or when it is static.also,another thing to be kept in mind is that when the body is moving at speed near to that of light,relativistic effects come into picture and the rest mass becomes reduced mass given by the formulaM0=m/square root of 1-v^2/c^2….which is always less than 1..