CBSE Class 12 · 2017 · ElectrostaticsShort Answer

(a) Write two properties by which electric potential is related to the electric field.
(b) Two point charges

q_{1}

and

q_{2}

, separated by a distance of

r_{12}

are kept in an external electric field. Derive an expression for the potential energy of the system of two charges in the field.

Solution

(a)(i) The electric field points in the direction in which the potential decreases most rapidly.
(ii) The field is the negative gradient of potential:

E = - \frac{d V}{d r}

equivalently, the field is normal to the equipotential surfaces.
(b) Work to bring

q_{1}

into the external field:

W_{1} = q_{1} V (r_{1})

Work to bring

q_{2}

, against the external field and the field of

q_{1}

W_{2} = q_{2} V (r_{2}) + \frac{1}{4 π ε _{0}} \frac{q _{1} q _{2}}{r _{12}}

U = q_{1} V (r_{1}) + q_{2} V (r_{2}) + \frac{1}{4 π ε _{0}} \frac{q _{1} q _{2}}{r _{12}}

CBSE Class 12 Board · 2017 · Subjective

Practise more: all CBSE board PYQs on Electrostatics →

CBSE Class 12 · 2017 · ElectrostaticsShort Answer

Solution

More board questions on Electrostatics