Figure shows the electric field lines around three point charges A, B and C 

(i) Which charges are positive?
(ii) Which charge has the largest magnitude? Why?
(iii) In which region or regions of the picture could the electric field be zero? Justify your answer.
(a) Near A         
(b) Near B
(c) Near C         
(d) Nowhere

An electric dipole of length 2 cm, when placed with its axis making an angle of 60^o with a uniform electric field, experiences a torque of  \(8\sqrt { 3 } \)N-m. Calculate the potential energy of the dipole, if it has a charge of \(\pm \)4nC.

A charge q is placed at the center of a cube of side l. What is the electric passing through each of the cube?

In the figure below the electric field lines on the left have twice the separation of those on the right.
(i) If the magnitude of the field of A is 40 N/C then what force acts on a proton at A?
(ii) What is the magnitude of the field at B?

Show that the force on each plate of a parallel plate capacitor has a magnitude equal to1/2 QE. where Q is the charge on the capacitor and E is the magnitude of electric field between the plates. Explain the origin of the factor 1/2.
Here, we can use the content that the work done in displacing the plates against the force is equal to the increase in energy of the capacitor.

A charge of 10μC is distributed uniformly over the circumference of a ring of radius 3 m placed on XY-plane with its centre at the origin. Find the electric potential at a point (0,0,4 m).

A cell of emf E and Internal resistance r gives a current of 0.5 A with an external resistance of 12 \(\Omega \) and a current of 0.25 A with an external resistance of 25 \(\Omega \) Calculate the
(i) internal resistance of the cell
(ii) emf of the cell

In a meter bridge, the null point is found at a distance of 40 cm from A. If a resistance of 12\(\Omega \) is connected in parallel with S, the null point occurs at 50 cm from A. Determine the values of R and S.

A 100 turns rectangular coil ABCD (in XY-plane) is hung from one arm of a balance figure. A mass 500 g is added to the other arm to balance the weight of the coil. A current 4.9 A passes through the coil and a constant magnetic field of 0.2 T acting inward (in XZ plane) is switched ON such that only arm CD of length 1 cm lies in the field. How much additional mass m must be added to regain the balance?

The magnetic force applied on CD by magnetic field must balance the weight.

Use Lenz's law to determine the direction of induced current in the situations described by figure.
(i) A wire of irregular shape turning into a circular shape.
(ii) A circular loop being deformed into a narrow straight wire