The value of current through the $20\,\Omega$ resistor is .................. $A$.

Five resistors are connected as shown in the diagram. The equivalent resistance between $A$ and $B$ is .............. $\Omega$.

The Wheatstone bridge principle is used to measure the specific resistance $(S_1)$ of a given wire,having length $L$ and radius $r$. If $X$ is the resistance of the wire,then the specific resistance is: $S_1 = X \left( \frac{\pi r^2}{L} \right)$. If the length of the wire is doubled,then the value of the specific resistance will be:

In a post office box arrangement used to determine the value of an unknown resistance,the unknown resistance should be connected between:

Five equal resistances are connected in a network as shown in the figure. The net resistance between the points $A$ and $B$ is

$A$ Wheatstone's bridge is balanced with a resistance of $625\, \Omega$ in the third arm,where $P, Q$ and $S$ are in the $1^{st}, 2^{nd}$ and $4^{th}$ arm respectively. If $P$ and $Q$ are interchanged,the resistance in the third arm has to be increased by $51\,\Omega$ to secure balance. The unknown resistance in the fourth arm is ............. $\Omega$.