**Heisenberg’s Uncertainty principle : **“Simultaneous and exact determination of the position and momentum of a sub-atomic particle, like electron moving with high speed is impossible”.

If x and p represent the uncertainties in the position and momentum respectively. Then according to Heisenberg

x . p ………….. (1)

The product of uncertainties in position (x) and momentum (p) of an electron cannot be less than . It can be equal or greater than .

Since momentum mass velocity, the equation (1) can be written as

x m (v) x v

If the position is determined accurately x = 0 and v = . That means the inaccuracy in measuring the velocity is . If velocity is determined accurately v = 0 and x = .

**Significance**** of Heisenberg’s Uncertainty principle :**

- This principle rules out the existence of definite paths or trajectories of electrons and other similar particles.
- This principle is significant only for the motion of microscopic objects and is negligible for that of macroscopic objects.
- In dealing with milligram size or heavier objects, the associated uncertainties are hard of any real consequence.