## Wednesday, November 21, 2012

### Signification of Electric Field

The signification of electric field is that the knowledge of electric intensity at any point can help us to calculate the force and direction of force.

Electric field at a point in  the space around a system of charges tells us the force a unit positive test charge would experience if placed at that point (without disturbing the system). Electric field is a characteristic of the system of charges and is independent of the test charge that we place at a point to determine the field. The term field in physics generally refers to a quantity that is defined at every point in space and may vary from point to point. Electric field is a vector field, since force is a vector quantity. consider the force between two distant charges q1, q2 in accelerated motion.

Now the greatest speed with which a signal or information can go from one point to another is c, the speed of light. Thus, the effect of any motion of q1 on q2 can not arise instantaneously. There will be some time delay between the effect (force on q ) and the cause (motion of q ). arise instantaneously. There will be some time delay between the effect (force on q2) and the cause (motion of q1). The accelerated motion of charge q1 produces electromagnetic waves, which then propagate with the speed c, reach q2 and cause a force on q2.  Thus, even though electric and magnetic fields can be detected only by their effects (forces) on charges, they are regarded as physical entities, not merely mathematical constructs.
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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?