STPM Physics Experiment 8 Earth's Magnetic Field (Second Term)

STPM Physics Experiment 8 (Second Term) Title: Earth’s Magnetic Field Results: Current, I/A 0.10 0.20 0.30 0.40 0.50 0.60 0.70

Average deflection of the magnet, θ/° 1 2 Mean 17.5 17.5 17.5 41.0 41.0 41.0 60.0 60.0 60.0 70.0 75.0 72.5 80.0 80.0 80.0 85.0 85.0 85.0 86.5 86.5 86.5

No.

Internal diameter of the solenoid, D/cm

1 2 3 4 5 Average

2.30 2.30 2.30 2.30 2.30 2.30

Average diameter of the wire used in the solenoid, d/cm 0.42 0.42 0.42 0.42 0.42 0.42

Length of the solenoid, L/cm

4.80 4.80 4.80 4.80 4.80 4.80

tan θ 0.32 0.87 1.73 3.17 5.67 11.43 16.35

Zero error of micrometer screw gauge = - 0.05mm Actual d = 0.42 - (- 0.05) = 0.47mm

Calculation:

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Discussions: (a) Precautions (i) The ammeter should be kept at least 50cm from the magnet. (ii) The fan is switched off and the windows are closed to minimize air movement. (iii) All connections of wire and devices must be tight. (iv) The experiment is carried out reasonably fast to prevent wires from heating up. (b) Sources of error (i) Successive turns of the solenoid are not perfectly bound together, resulting in error for the estimation of the number of turns. (ii) Inability to keep the magnet from swinging, resulting in inaccurate reading of θ. (c) Steps to overcome the weakness of the experiment (i) Count the number of turns for 1cm length of the solenoid, n. Then, obtain the number of turns in the solenoid using the estimation: N=nL. (ii) Repeat the experiment for a several times to increase the accuracy of the results. Conclusion: The horizontal component of the Earth’s magnetic field, BH is 1.4 x 10-5 T. Note: The graph is a curve. The gradient s is obtained from a tangent at I = 0.20A. The near actual value of BH = 2.5 x 10-5 T.