Difference between e.m.f and p.d

Wednesday, 30 October 2013


What is the fundamental Difference between e.m.f and p.d?

e.m.f: Electro motive force

p.d:  potential difference



a.The Next they first look implies that this force that causes current to flow. But it is not true that it is not by force, but energy provided by some require an active device such as a battery.

b.E.M.F keeps p.d while p.d. Causes the current to flow.

c.When we say that the EMF of the device is 2 V, this means that the machine provides the energy of 2 joules coulomb charge. When we say that the PD between points A and B of a circle is 2 V, this means that Coulomb energy give up charge of two Joule crossing from A to B.


 

The thermal speeds of free electrons are very large. In spite of these high speeds, why they fails to escape from the surface of a conductor?



      The thermal speeds of free electrons are very large. In spite of these high speeds, why they fails to escape from the surface of a conductor?

     
      Free electrons in a conductor are free only to the extent that they may move from one atom to another in the conductor. This is because the free electrons starting at the surface of conductive found behind the positive ions attract them back and pulling forward. So on the surface of a superconductor, free electron encounters forces that keep him out of the conductor surface. External energy is required to free electrons escape the conductor surface.
     



A wire is carrying current, is it charged or not


A wire is carrying current, is it charged or not?



No, the current in a wire is due to the drifting of free electrons in a definite direction. But the number of electrons in the wire at any instant is equal to the number of protons. So, the net charge on the wire is zero.


Why does a positive charge attract a negative charge



           Why does a positive charge attarct a negative charge?
 

 It is propensity of everybody to have least amount potential.
 Example: to obtain zero potential.
A positive charge means deficit of electrons while the negative charge indicates excess of electrons. For that reason, positive and negative charges attract each other to have minimum electric potential.



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