**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 = R

_{1}+ R_{2}for series connection and 1/R = 1/R_{1}+ 1/R_{2}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 (πr

^{2}/*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

*l*_{1}is the length of balance measured from the left end A, then,
X /R =

*l*_{1}/(100 —*l*_{1})
R and X are interchanged in gaps and the balancing length

*l*_{2}from the right end B is measured. Then,
X/R =

*l*_{2}/(100 —*l*_{2})
If

*l*= (*l*_{1}+*l*_{2})/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 πr**

^{2}/L
## 1 Comments

thank you. these questions are really helpful

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