STPM Physics Experiment 7 Wheatstone Bridge (Second Term)

STPM Physics Experiment 7 (Second Term) Title: Wheatstone Bridge Results: No. 1 2 3 4 5 Average a

Length of wire Rx between terminals C and D, x/cm 38.00 38.00 38.00 38.00 38.00 38.00 Distance of the balance point from A, a/cm 57.30 56.90 42.80 43.20

a1 a2 a3 a4 No. 1 2 3 4 5 Average

Let

Let

,∴

b1 b2 b3 b4

Diameter of wire Rx, d/mm 0.15 0.15 0.15 0.15 0.15 0.15

Calculation:

Since

b

( )

(

)

Distance of the balance point from B, b/cm 42.70 43.10 57.20 56.80 Zero error = - 0.04mm Actual d = 0.15 - (- 0.04) = 0.19mm

Discussions: (a) Precautions: (i) Do not drag the jockey along wire J in order to retain constant crosssectional area of the wire. (ii) Do not coil the constantan wire. (iii) All connections of the wire and other devices must be tight. (iv) The experiment is carried out without necessary delay in the process to prevent wire from heating up which would increase the resistance of the circuit, affecting the accuracy of the result. (b) Sources of error: (i) Use of nominal value of resistance of Rs instead of determining its rating. (ii) Assumption that galvanometer is ideal. (iii) Zero error of the micrometer screw gauge used. (iv) End error of metre rule due to wear and tear. (c) Steps to overcome the weakness of the experiment (i) Use a new metre rule. (ii) Eliminate zero error by calculation.

Conclusion: The resistivity of the wire Rx, ρ is 4.96 x 10-7 Ω m.