Six very long insulated copper wires are bound together to form a cable. The currents carried by the wires are $I_1=+10 \mathrm{~A}, I_2=-13 \mathrm{~A}, I_3=+10$ $\mathrm{A}, I_4=+7 \mathrm{~A}, I_5=-12 \mathrm{~A}$ and $I_6=+18 \mathrm{~A}$. The magnetic induction at a perpendicular distance of 10 cm from the cable is $\left(\mu_0=4 \pi \times 10^{-7} \mathrm{~Wb} / \mathrm{A}-\mathrm{m}\right)$

The fundamental frequency of sonometer wire increases by 9 Hz , if its tension is increased by $69 \%$, keeping the length constant. The frequency of the wire is

A potentiometer wire has length $L$ For given cell of emf $E$, the balancing length is $\frac{L}{3}$ from the positive end of the wire. If the length of potentiometer wire is increased by $50 \%$, then for the same cell, the balance point is obtained at length