121.

Four electric charge +q, +q, -q and -q  are placed at the corners of a square of side 2L (see figure). The electric potential at point A, mid-way between the two charges + q and +q, is

• 
• 

• zero

• zero

A parallel-plate air capacitor has capacity C, a distance of separation between plates is d a potential difference V is applied between the plates. Force of attraction between the plates of the parallel plate air capacitor is 

A series R -C circuit is connected to an alternating voltage source. Consider tow situations:

1. When the capacitor is air filled.
2. When the capacitor is mica filled.

Current through resistor is i and voltage across capacitor is V then

• V_a < V_b

• V_a > V_b

• i_a >i_b

• i_a >i_b

The electric potential V at any point (x, y,z), all in meters in space is given by V= 4x² volt. The electric field at the point (1,0,2) in volt/meter is 

• 8 along positive X-axis

• 16 along negative x- axis

• 16 along positive X- axis

• 16 along positive X- axis

Three charges, each +q, are placed at the corner of an isosceles triangle ABC of sides BC and AC, 2a. D and E are the midpoints of BC and CA. The work done in taking a charge Q from D to E is.

• 

• 

• zero

• zero

Two positive ions, each carrying a charge q, are separated by a distance d. If F is the force of repulsion between the ions, the number of electrons missing from each ion will be (e being the charge on an electron)

A series combination of n₁ capacitors, each of value of C_1, is charged by a source of potential difference 4V. When another parallel combination of n₂ capacitors, each of value C_2, is charged by a source of potential difference V, it has the same (total) energy stored in it, as the first combination has. The value of C₂, in terms of C₁, is then

Two parallel metal plates having charges +Q and -Q faces each other at a certain distance between them. If the plates are now dipped in kerosene oil tank, the electric field between the plates will

• become zero

• increase

• decrease

• decrease

Three capacitors each of capacitance C and of breakdown voltage V are joined in series. The capacitance and breakdown voltage of the combination will be

• C/3, V/3

• 3C, V/3

• C/3, 3V

• C/3, 3V

The electric potential at a point in free space due to a charge Q coulomb is Q x 10¹¹ V. The electric field at that point is