Final Exam Study Guide

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Final Exam Study Guide

Study Guide
The University of Vermont
Phys 012 - Elementary Physics
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Final Exam: Chapters 18-22, 24-30 Chapter 18 Electric Forces and Electric Fields Problem: In the rectangle in the drawing, a charge is to be placed at the empty corner to make the net force on the charge at corner A point along the vertical direction. What charge (magnitude and algebraic sign) must be placed at the empty corner? Answer: q = +3.0 μC Q = unknown charge θ = angle between A and empty corner kq2/(4d)2 = kqQ/(√(17) d)2 cosθ Q = -17√(17)/64 = -3.3μC Chapter 19 Electric Potential Energy and Electric Potential Problem: The potential at location A is 452 V. A positively charged particle is released there from rest and arrives at location B with a speed vB. The potential at location C is 791 V, and when released from rest from this spot, the particle arrives at B with twice the speed it previously had, or 2vB. Find the potential at B. Answer: qVA = qVB + ½ mvB2 qVC = qVB + ½ m(2vB)2 q(VC – VA) = 4(½ mvB2) – ½ mvB2 [q(VC – VA)]/3 = ½ mvB2 qVA = [q(VC – VA)]/3 + qVB VB = VA (VC-VA)/3 = +339 V Physics 012 1st Edition Chapter 20 Electric Circuits The drawing shows a circuit that contains a battery, two resistors, and a switch. What is the equivalent resistance of the circuit when the switch is (a) open and (b) closed? What is the total power delivered to the resistors when the switch is (c) open and (d) closed? Answer: (a) Req = R1 = 65 Ω (b) Req = (1/R1 + 1/R2)-1 = (1/65 + 1/96)-1 = 38.76 Ω (c) P = V2/Req = 92/65 = 1.25 W (d) P = V2/Req = 92/38.76 = 2.09 W Chapter 21 Magnetic Forces and Magnetic Fields Problem: A copper rod of length 0.85 m is lying on a frictionless table (see the drawing below). Each end of the rod is attached to a fixed wire by an unstretched spring that has a spring constant of k = 75 N/m. A magnetic field with a strength of 0.16 T is oriented perpendicular to the surface of the table.

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