The following circuit shows the use of potentiometer to measure the in

1.	The following circuit shows the use of potentiometer to measure the internal resistance of a cell(i) When the key is open, how does the balance point change, if the current from the driver cell decreases?(ii) When the key K is closed, how does the balance point change if R is increased keeping current from the driver cell constant?
Answer» (i) When current through driver cell decreases, the potential gradient across potentiometer wire decreases; so the balancing length \(l=\frac{E}{k}\) increases, so balance point is shifted to the right. (ii) With increase of R, the terminal p.d. across cell E increases and hence balancing length l \(=\frac{V}{k}∞\,V\) increases. So the balance point is shifted to the right.

The following circuit shows the use of potentiometer to measure the internal resistance of a cell(i) When the key is open, how does the balance point change, if the current from the driver cell decreases?(ii) When the key K is closed, how does the balance point change if R is increased keeping current from the driver cell constant?

Answer»

(i) When current through driver cell decreases, the potential gradient across

potentiometer wire decreases; so the balancing length \(l=\frac{E}{k}\) increases, so balance point is shifted to the right.

(ii) With increase of R, the terminal p.d. across cell E increases and hence balancing

length l \(=\frac{V}{k}∞\,V\) increases. So the balance point is shifted to the right.