Print Your Full Name General Physics II SCP 232- Exam 2 November 16, 2017 (You h

Question

Print Your Full Name General Physics II SCP 232- Exam 2 November 16, 2017 (You have 2 hours to finish the exam. You may use your equation sheet and a calculator only) Part I. Multiple choice: Circle one answer (1 pt each) 1. Which of the following statements is FALSE? (A) The resistance of a wire is proportional to its length. (B) The electric current in a metal wire is always opposite the direction the electrons are moving. (C) The drift velocity of electrons in a metal is nearly the speed of light 3 x 10 m/s (D) Real batteries have resistance. (E) The conductivity of a wire decreases when its temperature increases. 2. For the circuit shown in the diagram, the switch S is initially open and the capacitor is uncharged. The switch is then closed at time t = 0. How many seconds after closing the switch will the voltage across the capacitor be equal to the battery voltage? (MQ = 10° N) 90 pF 40 v w- 0.50 MO (A) 45s (B) 4.5s (C) 60s (D)225s (E) 45us 3. A negative charge, which is initially at rest, is placed in a region of space where there is a non-zero electric potential that is spatially varying. Which of the following statements best describes the behavior of the charge? (A) It moves from a region of high electric potential to a region of low electric potential. (B) It moves from a region of low electric potential to a region of high electric potential. (C) It does not move at all. (D) The charge moves along an equipotential surface. (E) It moves in the direction of the electric field.

Explanation / Answer

1)

Resistance R = rho*L/A

conductivity = 1/resistivity

resistivity increases wtih temperature

conductivty decreases

no particle can travel with light speed

OPTION (C)

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2)

In RC circuit the voltage across capacitor cahnges as V = Vmax*(1-e^-(t/RC))

for V = Vmax

40 = 40*(1-e^-(t/(0.5*10^6*90*10^-6)))

t = infinity means takes 225 us

for v = 39 v

39 = 40*(1-e^-(t/(0.5*10^6*90*10^-6)))

t = 166 s

for v = 40 t > 166 s

OPTION (D)

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3)

a negative charge always moves from low potential to high potential

OPTION (B)

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