Page 25 - Physics - XII

Q2. In a Wheatstone bridge, three resistances P, Q, and R are connected in the three arms and the
fourth arm is formed by two resistances S and S connected in parallel. The conditions for
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the bridge to be balanced will be
P 2 R P RS ( S ) P RS ( S ) P R
(a) (b) 1 2 (c) 1 2 (d) =
Q S S Q SS Q 2 SS Q SS
1 2 12 12 12
Q3. In a metre bridge experiment null point is obtained at 20 cm from one end of the wire when
resistance X is balanced against another resistance Y. Where will be the new position of null
point from the same end if one decides to balance a resistance of 4X against Y?

(a) 50 cm (b) 80 cm (c) 40 cm (d) 70 cm
Q4. A wire of uniform area of cross-section A, length l and resistance R is cut at the middle into

two equal parts of length l/2 each. Then, the resistivity of each piece compared to that of the
original becomes
(a) half (b) double (c) unchanged (d) unpredictable

Q5. Two wires of same material have length L and 2L and cross-sectional areas 4A and A respectively.
The ratio of their specifi c resistance would be

(a) 1 : 2 (b) 8 : 1 (c) 1 : 8 (d) 1 : 1
Q6. A resistance R is to be measured using a metre bridge. Student chooses the standard resistance S

to be 100 Ω. He fi nds the null point at l = 2.9 cm. He is told to attempt to improve the accuracy.
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Which of the following is a useful way? (NCERT Exemplar)

(a) He should measure l more accurately.
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(b) He should change S to 1000 Ω and repeat the experiment.

(c) He should change S to 3 Ω and repeat the experiment.

(d) He should give up hope of a more accurate measurement with a metre bridge.
Q7. Two resistances are connected in two gaps of a metre bridge. The balance is 10 cm is from the
zero end. A resistance of 20 Ω is connected in series with the smaller of the two. The null
point shifts to 20 cm. What is the value of the bigger resistance?

(a) 89 Ω (b) 144 Ω (c) 100 Ω (d) None of these

Q8. Which error of a metre bridge is removed when the known and unknown resistance are
interchanged?

(a) End error (b) Measurement error (c) Percentage error (d) parallex error
Q9. In a metre bridge, what is the eff ect on null defl ection of galvanometer when the radius of the
metre bridge wire is doubled?

(a) There will be no change. (b) Null point will shift to L /2 point.
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(c) Null point will shift to 2L point. (d) Null point will not be available.
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