What is the advantage of using thick metallic strips to join wires in a potentiometer?

While doing an experiment with a potentiometer as shown in the figure,it was found that the deflection is one-sided and $(i)$ the deflection decreased while moving the jockey from one end $A$ of the wire to the end $B$; $(ii)$ the deflection increased while the jockey was moved towards the end $B$.
$(i)$ Which terminal ($+$ or $-ve$) of the cell $E_1$ is connected at $X$ in case $(i)$ and how is $E_1$ related to $E$?
$(ii)$ Which terminal of the cell $E_1$ is connected at $X$ in case $(ii)$?

In the figure,the potentiometer wire of length $l = 100 \, cm$ and resistance $R = 9 \, \Omega$ is joined to a cell of emf $E_1 = 10 \, V$ and internal resistance $r_1 = 1 \, \Omega$. Another cell of emf $E_2 = 5 \, V$ and internal resistance $r_2 = 2 \, \Omega$ is connected as shown. The galvanometer $G$ will show no deflection when the length $AC$ is ............... $cm$.

When two cells are connected in series in a potentiometer circuit to assist each other,the balancing length is $6 \ m$. When they are connected in series to oppose each other,the balancing length is $2 \ m$. What is the ratio of the $EMF$ of the two cells?

In a potentiometer wire experiment, the $emf$ of a battery in the primary circuit is $20\,V$ and its internal resistance is $5\,\Omega$. There is a resistance box in series with the battery and the potentiometer wire, whose resistance can be varied from $120\,\Omega$ to $170\,\Omega$. The resistance of the potentiometer wire is $75\,\Omega$. Which of the following potential differences can be measured using this potentiometer?

$AB$ is a potentiometer wire as shown in the figure. If the value of $R$ is increased,in which direction will the balance point $J$ shift?