## Wednesday, November 21, 2012

### Concept Of Electric Field

Electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed at that point.

The charge Q, which is producing the electric field, is called a source charge and the charge q, which tests the effect of a source charge, is called a test charge.

Features of Electric field are given below.

i. Source charge Q must remain at its original location. Q itself is bound to experience an electrical force due to q and will tend to move. A way out of this difficulty is to make q negligibly small. The force F is then negligibly small but the ratio F/q is finite and defines the electric field:

ii. F is proportional to q, so the ratio F/q does not depend on q.

iii. For a positive charge, the electric field will be directed radially outwards from the charge. On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards.

iv. Since the magnitude of the force F on charge q due to charge Q depends only on the distance r of the charge q from charge Q, the magnitude of the electric field E will also depend only on the distance r. Thus at equal distances from the charge Q, the magnitude of its electric field E is same.

The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry.
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Some of these questions which may be asked in your Board Examination 2012-2013

Q1: What is a charge?

Q2: What is the SI unit of Charge?

Q3: What is charge on a neutron?

Q4: what is the change on an electron?

Q5: Explain what is an fundamental electronic charge?

Q6: what is main cause of charging?

Q7: Electrostatic forces are much stronger than gravitational forces. Give one example.

Q8: What is the value of charge on an electron? is a charge less than this value possible?

Q9: What is charge on a photon?