Exam 3--PHYS 202--S15

Transcription

1 Name: Class: Date: Exam 3--PHYS 202--S15 Multiple Choice Identify the choice that best completes the statement or answers the question 1 Consider this circuit Which of these equations is correct? 3 Which of these plots shows the current vs time for a charging capacitor? a I 1 +I 2 =I 3 b I I 1-2=0 c 2-2I 1 +8=0 d 2-2I 1-4+2I 2 =0 2 This multiloop circuit has 6 distinct currents Which of these equations is correct? a A b B c C d D 4 Which of these statements is always true? a the current for resistors in parallel is the same b resistors in parallel have the same voltage c the sum of the potentials for resistors in series is zero d the equivalent resistance of resistors in parallel is bigger than any one of the resistors 5 If the switch S is closed, what happens to the potential across R 2? a I 3 +I 6 =I 4 b I 1 +I 5 =I 4 c I 2 +I 6 =I 5 d I 1 -I 2 =I 3 a increases b decreases c stays the same d not enough information 1

2 6 Which of these statements about a household circuit is true: I The household circuit is a series circuit 9 This figure shows a wire between the poles of a magnet At the location of the wire, what is the direction of the magnetic field? II All devices in a household circuit operate at the same current III As you add more devices to a household circuit, the total current increases IV A ground fault circuit interrupt turns off if I in >I out for any particular device a I & IV b III & IV c III d II & III 7 What does GFCI do? a protects you from magnetic fields b provides a clear path to ground c turns off the circuit if the current exceeds a certain amount d checks if I in >I out 8 This is a true statement: a monopole does not exist Which of these is the best reason for why this is true? a ferromagnetic materials are able to be magnetized b a current in a wire can generate a magnetic field c permanent magnets are magnetic because their magnetic domains all line up d moving electrons cause magnetic fields a down b to the left c to the right d out of the page e up 10 Consider the figure in the previous question If a current in the wire is travelling out of the page, what is the direction of the force on the wire? a to the right b out of the page c down d to the left e up 11 The point A is equidistance between these two, long parallel wires What is the direction of the magnetic field at point A due to the two wires? a To the left b To the right c Into the page d Out of the page e There is no magnetic field at A 2

3 12 A positive particle approaches a current-carrying wire as shown here What direction will the particle go? 13 This loop of wire, which sits in a B-field directed to the right, has a current in the direction shown by the arrows The loop is allowed to rotate about an axis shown by the dotted line What is the direction the loop will turn? a left b right c out of the page d into the page e it will go back the way it came (up) a counterclockwise b clockwise 14 Which of these statements about the magnetic force on a charged particle travelling through a magnetic field is true: I The magnetic force is a centripetal force II The magnetic force is always perpendicular to the velocity III The magnetic force always causes circular motion a I & III b II & III c I & II d II only e all of these are true 3

4 Problem 15 (20 pts) Calculate the three currents in this circuit Extra credit (5pts): complete the calculation by Gaussian elimination (aka row reduction) 4

5 16 (15 pts) Consider this circuit a) What is the voltage across R 3, the 1-ohm resistor? V 3 = b) What is the total current in the circuit? I= c) What is the current through R 2, the 6-ohm resistor? I 2 = 17 (10 pts) In 2-4 sentences, describe how one of the household safety devices we discussed in class (third prong, GFCI, or circuit breaker) functions In your description, include the scenario in which the device would be useful and what happens when the device is utilized 5

6 18 (10 pts) Consider a series RC circuit for which R = 10 MΩ, C=50 µf, and ε=300 V Initially the capacitor has no charge a) When connected to the battery and resistor, what is the charge on the capacitor after 100 seconds? 19 (10 pts) A particle carrying a -10 C charge moves with velocity v = 3j -4k m/s through a uniform magnetic field B = 1i + 2j T What is the force, in vector notation, on the charged particle? b) How long does is required for the capacitor to become fully charged? c) Sketch a plot of how the charge on the capacitor varies with time as it is charging 6

7 20 (10 pts) A positive particle moves into the B-field of a mass spectrometer; the particle is moving at a speed of 4 m/s The magnetic field has a magnitude of 160 T, and the radius of the particle s path is 05 m Following is a table with the masses and charges of some imaginary particles Which is this particular particle? If the positive particle is traveling through a B-field as shown (in the -z direction), sketch the path it will take 7

8 ID: A Exam 3--PHYS 202--S15 Answer Section MULTIPLE CHOICE 1 ANS: D REF: S15 2 ANS: C 3 ANS: A REF: S15 4 ANS: B 5 ANS: B 6 ANS: B 7 ANS: D 8 ANS: D REF: S15 9 ANS: C REF: S15 10 ANS: E REF: S15 11 ANS: E 12 ANS: A REF: S15 13 ANS: A REF: S15 14 ANS: E PROBLEM 15 ANS: 16 ANS: 17 ANS: 18 ANS: a) 130 microcoulombs b) 50 s 19 ANS: 1

9 ID: A 20 ANS: Mamnium 2