$A$ wire is bent in the form of a circle of radius $2 \ m$. The resistance per unit length of the wire is $\frac{1}{\pi} \ \Omega/m$. $A$ battery of $6 \ V$ is connected between points $A$ and $B$ as shown in the figure. Given $\angle AOB = 90^{\circ}$,find the current flowing through the battery. (in $A$)

$(a)$ Three resistors $2 \; \Omega$,$4 \; \Omega$,and $5 \; \Omega$ are combined in parallel. What is the total resistance of the combination?
$(b)$ If the combination is connected to a battery of $emf \; 20 \; V$ and negligible internal resistance,determine the current through each resistor,and the total current drawn from the battery.

Two wires of equal diameters with resistivities ${\rho _1}$ and ${\rho _2}$ and lengths $x_1$ and $x_2$ are joined in series. The equivalent resistivity of the combination is

$A$ Copper $(Cu)$ rod of length $25 \, cm$ and cross-sectional area $3 \, mm^2$ is joined with a similar Aluminium $(Al)$ rod as shown in the figure. Find the resistance of the combination between the ends $A$ and $B$ (in $m\Omega$).
(Take Resistivity of Copper $= 1.7 \times 10^{-8} \, \Omega \cdot m$,Resistivity of Aluminium $= 2.6 \times 10^{-8} \, \Omega \cdot m$)

In the given star circuit,find the equivalent resistance between $A$ and $H$. (in $r$)

The current $I_{1}$ (in $A$) flowing through the $1\; \Omega$ resistor in the following circuit is: