What should be done in a meter bridge experiment to rectify a deflection in one direction indicated by the galvanometer if the null point is not reached?

To draw $i-\delta$ curve in order to find the angle for the minimum deviation, a student has to take observations in the range ${35}^{\circ }\mathrm{to} {60}^{\circ }$.  Which of the following statements is true about the number of observations to be taken by him?

A resistance wire connected in the left gap of the meter bridge balances a $10 \Omega$ resistance in the right gap. This happens at a point where the bridge wire is divided in the ratio of $3:2$. Assuming the length of the wire to be $1.5 \mathrm{m}$, calculate the length of the $1\Omega$ resistance wire?

In an experiment of finding focal length of a concave mirror by u-v method, a student prepares following graph of u versus v graph. 

Focal length of mirror is nearly

As shown, in a lab experiment, a student makes a graph based on his observations. In the u-v graph for a concave mirror, he drew lines OA, AB, and AD. what is the significance of point A?