# Potentiometer Viva Questions with Answers

Potentiometer Experiment Viva Questions with Answers

(i) What is a potentiometer?

Ans: It is an instrument to measure potential difference across two points accurately

(ii) What is its principle?

Ans: A uniform long resistances wire is mounted on a wooden board. When a steady emf is applied to the ends of this wire the fall of potential along the wire is proportional to the length

(iii) How can you increase the accuracy of the potentiometer?

Ans: It can be increased by increasing the length of the wire

(iv) A potentiometer is a better instrument than a voltmeter for measuring emf of a cell. why?

Ans: When we balance a cell against a potentiometer wire no current flows through the cell. Hence we measure the emf. When we use a voltmeter across a cell, a small current flow through the voltmeter and we are getting only the terminal potential difference of the cell

(v) What is meant by potential gradient?

Ans: It is the fall of potential per unit length (mm, cm or m) of the wire when a steady current flows though it.

(vi) What are the parts of a Daniel cell?

Ans: Zinc rod which is the negative plate is placed in a porous pot containing dil: H2SO4. Copper vessel acts as positive plate. The vessel contains copper sulphate solution.

(vii) Why don't you use Daniel cell in the primary circuit of a potentiometer?

Ans: The voltage is small and not steady. It cannot be used for a long time. It is not rechargeable.

(viii) What is the internal resistance of a primary cell due to?

Ans: It is the resistance of the solution. It depends on the nature of the solution, distance between the plates etc

(ix) The terminal potential of a battery while in use is smaller than the emf of the cell. Why?

Ans: Due to internal resistance of the cell there is a potential drop or 'lost volt' within the battery

(x) What is the function of the rheostat in the primary circuit?

Ans: To vary the current in the primary circuit so that we can repeat the experiment

(xi). What is a cell?

A cell is a device by which electric energy is generated due to chemical action taking place inside it.

(xii). Define primary cell.

Primary cell is a cell in which gives electrical energy from chemical energy. This cell cannot be recharged.

Eg: Dry cell, Daniel cell, Leclanche cell

(xiii). Define secondary cell.

Cell which stores electrical energy as chemical energy and returns it back as electrical energy, is called a secondary cell. This cell can be recharged.

(xiv). Why is potentiometer called so?

Potentiometer works on the principle that for a constant current, fall of potential along a uniform wire is directly proportional to its length.

(xv). Define e.m.f. of a cell.

e.m.f. of a cell is defined as the p.d between the terminals of the cell when the cell is in an open circuit.

(xvi). Why we prefer potentiometer rather than a voltmeter to measure e.m.f. of a cell?

Potentiometer method is a null deflection method. It does not draw any current from the source whose e.m.f. is to be measured. A voltmeter always draws some current.

(xvii). The e.m.f. of the cell used in the primary circuit of the potentiometer should be more than the potential difference to be measured. Why?

If it is not so, the balance point will not attain on the potentiometer wire.

(xviii). What is the principle of a potentiometer?

For a constant current, the potential drop across a wire is directly proportional to its length.

(xix). Which materials are suitable for potentiometer wire?

Manganin, constantan

(xx). What do you mean by sensitivity of a potentiometer?

Sensitivity of a potentiometer is the smallest potential difference that it can measure.

(xxi) Aim of the Potentiometer Experiment.

Ans:

(a) To compare the emfs of two cells.

(b) To determine the internal resistance of the given cell using a potentiometer

(xxii) Apparatus of the Potentiometer Experiment

Ans: Potentiometer, cells, resistance box, rheostat, galvanometer, two way key, single key, high resistance H R etc.

(xxiii) Theory to compare the emfs of two cells

Ans: If E1 and E2 are the emfs of two cells, E1 / E2 = l1 / l2; where l1and l2 are the balancing lengths of the potentiometer wire for the cells.

(xxiv) Procedure to compare the emfs of two cells.

Ans: An accumulator, a rheostat and a key are connected in series with the potentiometer with the positive of the accumulator connected to A. The cells whose e.m.fs are to be compared are connected to a two way key. The common terminals of the two way key are connected to A and to the jockey through a galvanometer and a high resistance (H R) as shown in the diagram. The first cell of e.m.f E1 is included in the circuit by suitably putting the two-way key and the balancing length l1 is measured. Without altering the rheostat in the primary circuit, the cell E2 is included in the circuit and the balancing length l2 is measured.

The emfs of the cell is compared using the equation, E1/ E2 = l1 / l2. The experiment is repeated for different positions of the rheostat and the mean value of E1 / E2is calculated.

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.