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Electricity and magnetism multiple choice questions

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Copper has one conduction electron per atom, that is, each atom contributes one electron that is free to move through the solid. The density of copper is 9 g/cm^3 and its molecular weight is 64 g/mole. A wire carries a current of 10 A. The cross sectioned area of the wire is 3 mm^2.

What is the current density in the wire
What is the number of conduction electrons per m^3
What is the conduction electron drift velocity

In the earth's atmosphere positive charges move toward the earth and negative charges move away from it. The total current is 1800 A. The average value of the electric field responsible for this current near the surface of the earth is 100 N/C. What is electrical resistivity of air at the surface of the earth? The radius of the earth is 6.37 x 10^6 m.

Last question is on a charged particle in a region of electric and magnetic filed.

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Cross sectional area = 3 mm^2 = 3 x 10^-6 m^2
Current density J = I/A = 10/ (3 x 10^-6) A/m^2

J = 3.33 x 106 A/m2

Solution provided does not show the 106 . If you notice, question # 36 uses the value of J in its calculation. ...

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1. The rotational speed of a pump shaft is 19.5 Hz. The frequency spectrum of
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A. 19.5 Hz. B. 39 Hz. C. 9.75 Hz. D. Always a sub-synchronous value of shaft

2. A ceiling fan has a rotational speed of 600 RPM and has five blades. The
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A. 60 Hz. B. 50 Hz. C. 30 Hz. D. 10 Hz.

3. The oil whirl phenomenon in a sleeve bearing (journal bearing), with a shaft
frequency of fr , occurs approximately at the following frequency.
A. 0.45 x fr. B. 1 x fr. C. 2 x fr. D. 2.45 x fr.

4. Which one of the following is not a condition-based (predictive maintenance)
A. Lubrication oil analysis
B. Vibration monitoring
C. Periodic replacement of pump seals
D. Ultrasonic testing for flaw detection
E. Thermography for inspecting hot spots on equipment

5. The coherence function between two detector signals is given by

A. 1/10. B. ½. C. 0.0 D. infinity.

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