The insulated plates of a charged parallel plate capacitor (with small separation between the plates) are approaching each other due to electrostatic attraction. Assuming no other force to be operative and no radiation taking place, which of the following graphs approximately shows the variation with time (t) of the potential difference (V) between the plates?

Three capacitors of capacitance 1.0, 2.0 and 5.0 $$\mu$$F are connected in series to a 10 V source. The potential difference across the 2.0$$\mu$$F capacitor is

Six wires, each of resistance r, are connected so as to form a tetrahedron. The equivalent resistance of the combination when current enters through one corner and leaves through some other corner is

Consider the circuit shown in the figure.


The value of the resistance X for which the thermal power generated in it is practically independent of small variation of its resistance is