Page 24 - Physics - XII

Q5. What is a null point?
Ans. It is a point on the wire, keeping jockey at which the galvanometer shows no defl ection.

Q6. What is the material of wire of metre bridge?
Ans. The material of wire of metre bridge is constantan.
Q7. Why constantan is used in bridge wire?
Ans. (i) The resistivity of the constantan is high.
(ii) The temperature coeffi cient of resistance is very small.

Q8. What is a Wheatstone Bridge?
Ans. It consists of four resistances P, Q, R, and S forming a close network of four arms AB, BC, AD,
and DC such that a cell is connected between A and C and a galvanometer is connected between B
and D.
Q9. What is a metre bridge?
Ans. It is an instrument used to determine the unknown value of the given resistance.

Q10. Why is it called a metre bridge?
Ans. The length of the wire is one metre and it is based on the principle of Wheatstone bridge. That is
why, it is called a metre bridge.
Q11. Comment on the diff erence between theoretically expected and experimentally obtained values
of the eff ective resistances. (NCERT)
Ans. The theoretically expected values of the eff ective resistance are calculated by the formula of eff ective
resistance of series and parallel combination.
For experimentally obtained values, we experimentally obtained the values of the eff ective resistance
using a metre bridge with error.

Q12. Given n resistors of resistance R each, how will you combine them to get the maximum and the

minimum eff ective resistance? (NCERT)
Ans. To get the maximum eff ective resistance, all the resistors are connected in series and the maximum
eff ective resistance obtained in this case will be nR.

To get the minimum eff ective resistance, all the resistors are connected in parallel and the minimum
R
eff ective resistance obtained in this case will be .
n
Q13. Identify some method(s) to reduce the eff ect of ‘end-resistance’ at connections between the
wire and copper strip or because of the improper soldering of wire. (NCERT)
Ans. We can reduce the eff ect of ‘end-resistance’ by rubbing the soldered portion with sand paper.

COMPETENCY BASED QUESTIONS

Multiple Choice Questions

Q1. Resistivity of a given conductor depends upon
(a) temperature (b) length of conductor

(c) area of cross-section (d) shape of conductor

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