Four equal resistors,each of resistance $10 \,\Omega$,are connected as shown in the circuit diagram. The equivalent resistance between $A$ and $B$ is ............. $\Omega$.

Two resistance wires on joining in parallel the resultant resistance is $\frac{6}{5} \ \Omega$. One of the wires breaks,the effective resistance is $2 \ \Omega$. The resistance of the broken wire is ............ $\Omega$.

The equivalent resistance of a group of resistances is $R$. If another resistance is connected in parallel to the group,its new equivalent becomes $R_1$,and if it is connected in series to the group,its new equivalent becomes $R_2$. We have:

Two resistances $r_1$ and $r_2$ $(r_1 < r_2)$ are joined in parallel. The equivalent resistance $R$ is such that

Two wires $A$ and $B$ are made of the same material and have the same mass. The radius of wire $A$ is twice the radius of wire $B$. If wires $A$ and $B$ are connected in parallel,the equivalent resistance will be:

An electric kettle has two filaments. The first filament boils a certain amount of water in $10 \text{ minutes}$ and the second filament boils it in $15 \text{ minutes}$. If both filaments are connected in parallel,the water will boil in .............. minutes.