A charge of 10 e.s.u. is placed at a distance of 2 cm from a charge of 40 e.s.u. and 4 cm from another charge of 20 e.s.u. The potential energy of the charge 10 e.s.u. is: (in ergs) 

1.	87.5	2.	112.5
3.	150	4.	250

In a certain charge distribution, all points having zero potential can be joined by a circle S. Points inside S have positive potential, and points outside S have a negative potential. A positive charge, which is free to move, is placed inside S. What is the correct statement about S:

Two charges q₁ and q₂ are placed 30 cm apart, as shown in the figure. A third charge q₃ is moved along the arc of a circle of radius 40 cm from C to D. The change in the potential energy of the system is $\frac{q_3}{4\pi {\epsilon }_0}k$, where k is:

If the dielectric constant and dielectric strength be denoted by k and x respectively, then a material suitable for use as a dielectric in a capacitor must have:

1. high k and high x.

2. high k and low x.

3. low k and low x.

4. low k and high x.

Three capacitors of capacitances 3 μF, 9 μF and 18 μF are connected once in series and another time in parallel. The ratio of equivalent capacitance in the two cases $\left(\frac{{\displaystyle C_s}}{{\displaystyle C_p}}\right)$ will be:

1. 1 : 15

2. 15 : 1

3. 1 : 1

4. 1 : 3

Four capacitors each of capacity 3 μF are connected as shown in the adjoining figure. The ratio of equivalent capacitance between A and B and between A and C will be:

1. 4: 3

2. 3: 4

3. 2: 3

4. 3: 2

A parallel plate condenser is filled with two dielectrics as shown. Area of each plate is A metre² and the separation is t metre. The dielectric constants are k₁ and k₂ respectively. Its capacitance in farad will be:

1. $\frac{{\epsilon }_{0}A}{t}(k_1+k_2)$

2. $\frac{{\epsilon }_{0}A}{t}.\frac{k_1+k_2}{2}$

3. $\frac{2{\epsilon }_{0}A}{t}(k_1+k_2)$

4. $\frac{{\epsilon }_{0}A}{t}.\frac{k_1-k_2}{2}$

In the connections shown in the adjoining figure, the equivalent capacity between A and B will be:

1. 10.8 μF

2. 69 μF

3. 15 μF

4. 10 μF

The diagrams below show regions of equipotentials.

A positive charge is moved from A to B in each diagram. Then:

A capacitor of 2 $\mu F$ is charged as shown in the figure. When the switch S is turned to position 2, the percentage of its stored energy dissipated is: