Explain with a proper diagram how an ac signal can be converted into dc(pulsating) signal with an output frequency double the input frequency using the PN junction diode. Give its input and output waveforms.

A small town with a demand of $1200 KW$ of electric power of $220 V$ is situated $20 Km$ away from an electric plant generating power at $440 V$. The resistance of the two wireline carrying power is $0.5 \Omega per km.$ The town gets power from the line through a $4000-220 V$step-down transformer at a sub-station in the town. Estimate the line power loss in the form of heat.

Three-point charges $q, –4q$ and $2q$ are placed at the vertices of an equilateral triangle ABC of side $l$ as shown in the figure. Find out the amount of the work done to separate the charges at infinite distance.

The Force of electrostatic repulsion between to small positively charged objects A & B is $3.6\times {10}^5 \mathrm{N}$. When AB is $0.12 \mathrm{m}$
What is the force of repulsion of AB is increased to

$$\begin{gathered} \left(a\right) 0.24 \mathrm{m} \\ \left(b\right) 0.30 \mathrm{m} \end{gathered}$$

The effective resistance between points A and B of the network shown in figure is

For the given circuit, find the current through $1 \mathrm{\Omega }$, $2 \mathrm{\Omega }$ and $3 \mathrm{\Omega }$  resistors.