Although electrons in metal move in haphazard directions at many times the speed of sound, the drift speed of electrons that compose electric current is

A) a fraction of a centimeter per second.
B) many centimeters per second.
C) the speed of a sound wave.
D) the speed of light.
E) none of the above


Answer: A

Physics & Space Science

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At the point of fission, a nucleus of U-238, with 92 protons is divided into two smaller spheres each with 46 protons and a radius of 5.9 × 10^?15 m. What is the repulsive force pushing the two spheres apart when they are just touching one another? (The mass of the U-238 nucleus is 3.98 × 10^?25 kg.)

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A rectangular plate (a 5 120 mm, b 5 160 mm) is subjected to compressive stress ?x 5 24.5 MPa and tensile stress ?y 5 15 MPa. The ratio of the normal stress acting perpendicular to the weld to the shear stress acting along the weld is approximately:


(A) 0.27
(B) 0.54
(C) 0.85
(D) 1.22

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If the energy gap in a semiconductor is 1.0 eV, which of the following energy photons will have the lowest absorption coefficient in the semiconductor?

(a) 0.2 eV (b) 0.8 eV (c) 1.2 eV (d) 2 eV

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Capacitors in Combination: A 5.0-?F, a 14-?F, and a 21 ?F capacitor are connected in parallel. How much capacitance would a single capacitor need to have to replace the three capacitors?

A. 40 ?F B. 21 ?F C. 5.0 ?F D. 14 ?F

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