# Meter Bridge Viva Questions with Answers

Viva Questions and Answers for Meter Bridge Experiment
(i) Why is Wheatstone Bridge so called?

Ans: The principle was discovered by Sir Charles Wheatstone

(ii) What is a Metre Bridge. Why is it so called?

Ans: It is an instrument for comparing resistances. The bridge wire has a length of one metre

(iii) What is the principle of Wheatstone Bridge?

Ans: When the bridge is balanced P/Q = R/S

(iv) Can you find very high resistances accurately with the help of a metre bridge?

Ans: No

(v) Why is the galvanometer is graduated both sides of zero?

Ans: If the jockey is pressed on either side of balance point the deflection in the galvanometer are in opposite directions

(vi) Can we use an ammeter instead of a galvanometer?

Ans: Ammeter is not sensitive compared with a galvanometer. Moreover it is graduated with zero at one end

(vii) What is the material of the bridge wire: What is the criterion for selections?

Ans: Manganin wire is used. Low temperature coefficient

(viii) Why are copper strips on the bridge thick?

Ans: To minimise resistance

(ix) Why is it desirable to have null point as near the centre as possible?

Ans: This will minimise end corrections. Interchanging the resistance also minimises end correction.

(x) When is Wheatstone Bridge most sensitive?

Ans: It is most sensitive when P, Q, R and S are of the same order of magnitude

(xi) What are the laws of combination of resistances?

Ans: R = R1 + R2 for series connection and 1/R = 1/R1 + 1/R2 for parallel connection.

(xii) Aim of Meter Bridge Experiment

Ans:
(a)To determine the resistivity of the material of a wire
(b) To verify the laws of resistances.

(xiii) Apparatus of Meter Bridge Experiment

Ans: The metre bridge, resistance box, resistance wire, battery, high resistance (HR), key etc.
A metre bridge contains a uniform resistance wire, AB having 1 m length, kept extended between two copper strips set on a wooden board. Another copper strip set centrally on the board leaves two gaps amid the strips. The copper strips are provided with terminals.

(xiv) Theory of Meter Bridge Experiment to determine the resistivity

Ans: If l is the balancing length of the bridge wire from the side of the unknown resistance X and R is the known resistance,

X/R = l/(100 —l);

Therefore, X = R [l/(100 —l)]

Resistivity of X is ρ = X x (πr2 / l); where r is the radius and l is the length of the wire X.

(xv) Procedure of Meter Bridge Experiment to determine the resistivity of the material of a wire.

Ans: The unknown resistance X is connected in the left gap and a resistance box R in the right gap. A battery is connected between A and B. A galvanometer is connected between C and a jockey that can slide along the bridge wire.

A suitable resistance R is taken in the box and circuit is closed. The position of the jockey is adjusted so that the galvanometer shows null deflection.

If l1 is the length of balance measured from the left end A, then,
X /R = l1/(100 — l1)

R and X are interchanged in gaps and the balancing length l2 from the right end B is measured. Then,
X/R = l2/(100 — l2)

If l = (l1 +l2)/2;
then X/R = l/(100 — l)
Therefore, X— R[l/(100 — l)]

The experiment is repeated for different values of R; but the balancing point must be near the middle of the bridge wire. In each case X is calculated. From these, the mean value of X is calculated. The radius r of the wire is measured using screw gauge. The length `L' of the wire is measured by a metre scale. Resistivity of the wire is calculated using the equation,

ρ = X πr2/L

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