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Q.
In the potentiometer experiment shown in figure-$3.365$, the null point length is $l$. Choose the correct options given below
Current Electricity
Solution:
If switch $S$ is open,
$i_{1} \rho l=E_{2}$
where $i_{1}$ is the current in primary circuit and $\rho$ is resistance per unit length of potentiometer wire.
Thus at null point balancing length is given as
$l=\frac{E_{2}}{i_{1} \rho}$
If jockey is shifted towards right, resistance in primary circuit will increase so current $i_{1}$ will decrease and $l$ will increase.
If $E_{1}$ is increased, $i_{1}$ will also increase so $l$ will decrease.
As $l \propto E_{2}$ with $E_{2}, l$ will increase.
If switch is closed then null point will be obtained corresponding to the potential difference
$V_{2}=E_{2}-i_{2} r_{2}$
Which is less than $E_{2}$ so null point balancing length will decrease.
