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| Electric Field |
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The electric field or electric field strength is the electrostatic force acting on a small positive test charge placed at that
point. If  is the electrostatic
force experienced by a test charge q at a point, then the electric field intensity at that point is given by |
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| S.I unit of electric field intensity is newton/coulomb(NC-1). |
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| Note: |
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| If the test charge is not small, then the electric field may be affected by the test charge and hence we modify the above equation as follows: |
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| Consider a charge Q at the origin of the co-ordinate system. Let a test charge q be placed at a distance r from the origin. |
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| The magnitude of the electric field intensity due to a point charge is |
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Consider a system of charges q1, q2, ………..qn placed at distances r1, r2, ………..rn with respect to some origin. Then the electric field intensity due to all these charges at a point is found out using the  intensity due to the number of charges q1, q2, ………..qn. Then the  given by the superposition theorem. |
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| Electric field intensity due to the nth charge is |
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| Magnitude of the electric field intensity is given by the equation |
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| Calculations of electric field intensity are of tremendous importance due to the technological applications of electric forces. To determine the trajectories of electrons in a T.V. tube, in an accelerator used in cancer radiotherapy, or of charged particles in a semiconductor electronic device we have to know the detailed nature of the electric field acting on the charges. Thus electric field helps us determine the electrical environment of a system of charges. |
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