Q.Define intensity of electric field at a point. Derive an expression for the intensity due to a point charge.

Electric field is the force per unit positive test charge at a point, $\vec E=\vec F/q_0$, a vector quantity measured in newton per coulomb.

Definition

The electric field $\vec E$ at a point due to a charge distribution is defined as the electrostatic force $\vec F$ that would act on a very small positive test charge $q_0$ placed at that point, per unit charge:

$\vec E = \lim_{q_0\to0}\dfrac{\vec F}{q_0}$

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Electric field is the force per unit positive test charge at a point, $\vec E = \vec F/q_0$, directed along the force that would act on a small positive charge there.

Definition

The electric field $\vec E$ at any point in space, due to a charge or a charge distribution, is defined as the electrostatic force $\vec F$ experienced by a very small positive test charge $q_0$ placed at that point, divided by the magnitude of the test charge, taken in the limit that $q_0$ is vanishingly small (so that it does not disturb the original charge distribution):

$\vec E = \lim_{q_0\to 0}\dfrac{\vec F}{q_0}$

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