The value of the shunt resistance that allows $10 \%$ of the main current through the galvanometer of $99 \Omega$ is

In which of the following figures, the p.n. junction diode is reverse biased?

Two tuning forks of frequencies 256 Hz and 258 Hz are sounded together. The time interval between two consecutive maxima is

' $n$ ' identical small spherical drops of water, each of radius ' $r$ ' and charged to the same potential ' v ' are combined to form a big drop. The potential of a big drop is