In the following network, the current flowing through $15 \text{ } \Omega$ resistance is (in $\text{ A}$)

Kirchhoff's first law,$i.e.$,$\Sigma i = 0$ at a junction,is based on the law of conservation of:

Five resistances are connected as shown in the figure. The effective resistance between the points $A$ and $B$ is

$A$ uniform wire of length $200 \, cm$ is connected to a battery, two resistors and a galvanometer as shown in the figure. The galvanometer shows null deflection when the jockey $J$ is at $80 \, cm$ from point $A$. If the resistor $R_2$ is shunted with $30 \, \Omega$ resistance, the galvanometer shows null deflection when the jockey $J$ is at $100 \, cm$ from point $B$. Then the values of $R_1$ and $R_2$ respectively are

The current between $B$ and $D$ in the given figure is .............. $A$.

State the principle of a Wheatstone bridge.