A meter bridge set up as shown to determine end correction at $A$ and $B$ . When a resistance of $15\,\Omega $ is used in left gap and of $20\,\Omega $ in right gap, then null point comes at a distance $42\ cm$ from $A$ . When these resistances are interchanged null point comes at a distance $57\ cm$ from $A$ . Values of end corrections are

What is Wheatstone bridge ? Explain its principle.

$A$ 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 …………. $\Omega$

For what value of unknown resistance $X$, the potential difference between $B$ and $D$ will be zero in the circuit shown in the figure …………… $\Omega$

In meter bridge or Wheatstone bridge for measurement of resistance, the known and the unknown resistances are interchanged. The error so removed is