Heisenberg’s Uncertainity principle:
When we are studying a large moving objects say a planet, then we can follow its definite path on which it travels. If we know its initial position and momentum, then we can predict its position and momentum at any other time. But this is not possible for electron, proton and neutron which are microscopic particles. Heisenberg has given a principle in this connection. He says that it is impossible to measure simultaneously both the position and momentum of a microscopic particle with accuracy or certainty.
Mathematically this principle can be put as follows:
These two uncertainties are inversely proportional to each other. So, if position of the microscopic principle is known with more accuracy, then there will be more uncertainty in its momentum and vice versa.
Physical Concept of Uncertainity Principle:
In order to know the position of an object, we throw the photons of light upon them. If we want to have the idea for the position of electron, then the photons of X-rays region have to be used because their wavelength are very small and the possibility for the hitting of electron is there. During this hitting, the photons transfers some of its energy to the electron. Therefore, the velocity and hence the momentum of electron changes.
If we use the photons of longer wavelength say of visible region, the velocity and the momentum will not change appreciably because longer wavelengths rarely find the chance to hit the electron. But its position can be not determined because object will not be visible.
Keep it in mind that, the uncertainity is not due to lack of better techniques for the measurement of position and momentum. It is due to the reason that we cannot observe the microscopic objects without disturbing them. Uncertainity principle is not applicable to stationary electron because the stationary state the velocity of an electron is zero. As a result, position of electron can be accurately determined. But both positions and velocities of electron cannot be determined accurately.