Question: Q. 5. (i) State the working principle of a potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf’s of two primary cells. Obtain the required expression used for comparing the emfs.
(ii) Write two possible causes for one sided deflection in a potentiometer experiment.
R [Delhi I, II, III 2013]
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Solution:
Ans. (i) Principle : Try yourself Similar to Q. 2 Short Answer Type Questions-II
(ii) (a) When the driver cell / source cell has emf less than the emf of the cells to be compared.
1
(b) When the positive end of the potentiometer wire is connected to negative terminal of the cell whose emf is to be compared / determined.
[CBSE Marking Scheme 2013] 1
(AI Q. 6. (i) Draw a circuit diagram of a metre bridge used to determine the unknown resistance $R$ of a given wire. Hence derive the expression for $R$ in terms of the known resistance $S$.
(ii) What does the term ’end error’ in a metre bridge circuit mean and how is it corrected? How will the balancing point be affected, if the positions of the battery and galvanometer are interchanged in a metre bridge experiment? Give reason for your answer. R [Delhi Compt I, II, III 2017]
Ans. (i) Labelled circuit diagram of metre bridge & derivation of expression of $R$. (ii) Meaning of end error and its correction $1 / 2+1 / 2$ Effect of balancing Length Reason
[CBSE Marking Scheme 2017]
Detailed Answer :
(i) Try yourself Similar to Q. 9, Short Answer Type Questions-II.
(ii) The error which arises on account of resistance of copper strips and the connecting wire at both ends of the metre bridge is called end error.
$1 / 2$
It is minimized by adjusting the balance point near the middle point of the bridge.
$1 / 2$
No effect, as the bridge remains balanced. $1 / 2+1 / 2$
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UNIT - III
