q v A. Toward the top of this page B. Toward the bottom of this page C. Into this page D. Out of this page screen

Transcription

1 q v? An electron moves horizontally toward a screen. The electron moves along the dotted path because of a magnetic force caused by a magnetic field. In what direction does that magnetic field point? A. Toward the top of this page. Toward the bottom of this page C. Into this page D. Out of this page screen

2 uniform magnetic field C +Q D: down and slightly out of this page A A uniform magnetic field points straight up in a laboratory on Earth. A positively charged ball is dropped in this field, and gravity makes it fall (at least initially) straight down. Which of the following best show its path?

3 electron An electron approaches the pole of bar magnet at high speed. The arrows on this diagram show the direction of the magnetic field and the direction of the electron s initial velocity. What type of pole (N or S) is the electron approaching and in which direction will the electron move? A. S, into page. S, out of page C. N, into page D. N, out of page

4 What happens to a positive charge that is placed at rest in a uniform magnetic field? (A uniform field is one whose strength and direction are the same at all points.) A. It moves with a constant velocity since the force has a constant magnitude.. It moves with a constant acceleration since the force has a constant magnitude. C. It moves in a circle at a constant speed since the force is always perpendicular to the velocity. D. It remains at rest since the force and the initial velocity are zero.

5 uniform magnetic field uniform magnetic field magnet battery thin wire The picture above shows a device very similar to one used in class. A battery drives a current through a thin wire which is suspended above a magnet. When the battery is connected the thin wire moves into the page. What sort of pole is the top of the magnet? A. N. E C. S D. W a b d There is a current flowing clockwise around a square loop which is surrounded with a uniform magnetic field pointing to the right. The torque on this loop will try to rotate the loop so: A. side a moves out of the page. side b moves out of the page C. side c moves out of the page D. side d moves out of the page c

6 uniform magnetic field uniform magnetic field a b d c A. wire a moves out of the page. wire b moves out of the page C. wire c moves out of the page D. wire d moves out of the page

7 Long straight wires, carrying equal currents, are placed at the corners of an equilateral triangle. Which vector best displays the direction of the magnetic field at X? C A D One current is now reversed... Another current is reversed...

8 I out A C P D I in Wire 1 has a large current I flowing out of the page ( ), as shown in the diagram. Wire 2 has the same current I, but flowing into the page ( ). In what direction does the magnetic field point at position P?

9 A C D Crossed wires each carry the same current I. Which point has a magnetic field pointing out of the page? Into the page? Zero?

10 II I uniform magnetic field III IV V beam source In this case the particles all have the same speed, Which of the below statements properly assigns particles with paths? A. I=electron; V=proton. IV=deuteron and α; V=proton C. I=proton; II=deuteron D. I=electron; III=α; IV=deuteron

11 Each of the below loops carries a current I. Which has the biggest magnetic dipole moment? Smallest? A C D

12 µ #1 The figure shows three different configurations of a magnetic dipole µ placed in a uniform magnetic field. Which of the below options best describes the relationship between the magnitude of the torque experienced by the dipole in these configurations. (τ 1 denotes the magnitude of the torque in configuration #1, etc.) µ µ #2 #3 A. τ 1 > τ 2 > τ 3. τ 1 < τ 2 < τ 3 C. τ 1 = τ 2 = τ 3 D. τ 1 = τ 3 < τ 2 Consider the potential energy of the magnetic dipole in the uniform magnetic field of the previous problem. Which of the below options best describes the relationship between the potential energy of the dipole in these configurations. (U 1 denotes the potential energy in configuration #1, etc.) A. U 1 > U 2 > U 3. U 1 < U 2 < U 3 C. U 1 = U 2 = U 3 D. U 1 = U 3 < U 2

13 uniform magnetic field uniform magnetic field The magnetic field and the circular loop lie in the plane of this page. The magnetic flux through the loop is: A +πr 2 πr 2 C +2πr D zero

14 I infinite wire Consider the case of an infinite wire, carrying a current I sitting on the z axis. The magnetic flux through a disk of radius R, sitting in the xy plane and centered on the origin is: A. 2 π R R. + π R 2 C. π R 2 D. 0

15 In this oscilloscope trace the vertical scale is 1V/div and the horizontal scale is 2ms/div. Vrms is most nearly? A:3 :2 C:1 D:0 The period is most nearly: A:12ms :8ms C:6ms D:2ms

16 Secondary circuit Primary circuit N S The south pole of a bar magnet has been sitting near the end of a solenoid. The bar magnet is now moved vertically towards the solenoid. Which way will the current flow in the straight section? A. Up. Down A A. Clockwise. Counter Clockwise A long straight wire and a square loop of wire sit in the plane of this sheet of paper. A circular loop of wire sits in a plane perpendicular to the long straight wire. For several minutes there has been a current flowing up the long straight wire; that current is now reduced. Which way will the induced current flow in the square and the circle? A current has been flowing through the primary circuit in the direction indicated. This current is now reduced to zero. What is the direction of the current induced in the secondary circuit A

17 N Secondary circuit Primary circuit S A. Left. Right The south pole of a bar magnet is approaching the solenoid A. Up. Down The current shown flowing through the primary circuit is increasing A. Clockwise. CCW A long straight wire and a square loop of wire sit in the plane of this sheet of paper. A circular loop of wire is centered on the long wire, but sits in a plane perpendicular to this sheet of paper. For several minutes there has been no current flowing in any wire. A battery (not shown) is connected and a current starts to flow to the right through the long straight wire.

18 1 mα 1 ma 100 µα 1 ma 10 kω 10 mh A 10 V 1 µs 1 µs C D 10 ms 1 µs

19 100 V 100 mv 1 V 100 V A 1 µs 0.1 s C D 1 ms 10 ms A generator has 10,000 turns around a square loop with side 1cm and is spinning at ω=100rad/s. What does is the output voltage?

20 uniform magnetic field uniform magnetic field A C uniform magnetic field uniform magnetic field D

21 The below figure shows, in cross section, three identical solid cylindrical wires of radius (R) carrying a current I distributred uniformly throughout the cross section. Also shown is three Amperian loops; The three have differing radius (r). What is the magnitude of the current I through these loops as a function of r? Which of the below plots best displays the relationship between I and r? R r Amperian loop solid wire I A I r r I C I D r r

22 The below figure shows, in cross section, three identical solid cylindrical wires of radius (R) carrying a current I distributred uniformly throughout the cross section. Also shown is three Amperian loops; The three have differing radius (r). What is the magnitude of the current I through these loops as a function of r? Which of the below plots best displays the relationship between I and r? r R Amperian loop solid wire I A I r r I C I D r r

23 The below figure shows, in cross section, three solid cylindrical wires of differing radius (R) but all carrying the same current I distributed uniformly throughout the cross section. Also shown is three Amperian loops; The three have the same radius (r). What is the magnitude of the current I through these loops as a function of R? Which of the below plots best displays the relationship between I and R? Amperian R r loop I A I solid wire R R I C I D R R

24 The below figure shows, in cross section, three solid cylindrical wires of differing radius (R) but all carrying the same current I distributred uniformly throughout the cross section. Also shown is three Amperian loops; The three have the same radius (r). What is the magnitude of the magnetic field around these loops as a function of R? Which of the below plots best displays the relationship between and R? Amperian R r loop A solid wire R R C D R R

25 The below figure shows, in cross section, three solid cylindrical wires of differing radius (R) but all carrying the same current I distributred uniformly throughout the cross section. Also shown is three Amperian loops; The three have the same radius (r). What is the magnitude of the magnetic field around these loops as a function of R? Which of the below plots best displays the relationship between and R? Amperian loop r R A R R C D R R

26 The below figure shows, in cross section, three identical solid cylindrical wires of radius (R) carrying a current I distributred uniformly throughout the cross section. Also shown is three Amperian loops; The three have differing radius (r). What is the magnitude of the magnetic field through these loops as a function of r? Which of the below plots best displays the relationship between and r? r R Amperian loop solid wire A r r C D r r

27 y 1 A 2 A 3 A 2 A A C x Which amperian loop encloses the most current (positive numbers are larger than negative numbers)

28 20 X Y 10 t (ms) A. X leads Y. Y leads X C. X lags Y D. Y lags X If this is an L... A. X is I, Y is V. X is V, Y is I If this is a C... A. X is I, Y is V. X is V, Y is I

29 Voltage (V) t (ms) A. 10 V 1. V rms A T. 14 V 2. V m or V p f C. 28 V 3. V p-p C ω D. 14 V D. 2000

30 The ac generator in this circuit has a fixed voltage (V) and frequency (f). We seek to maximize the current through a particular coil with inductance L. Compared to the simple circuit shown, the current through the coil could be increased by: A. Adding a resistor in parallel to L. Adding a capacitor in series with L C. Adding an inductor in parallel with L D. It is not possible to increase the current through the coil by adding components.

31 A ωt ωt C ωt D ωt

32 A ωt If the solid arrow represents the phasor for V R which case shows: V L? V C? ωt C ωt

33 10 Ω 0.1 µf 0.1 H A What value of ω would maximize the current? A:10 5 :10 4 C:10 3 D:10 2 If the phasor diagram is as shown, ω is A. higher than resonance. lower than resonance C. at resonance ωt

34 10 Ω 0.1 µf 0.1 H A If R < X L < X C, which component will heat the most? A:R :L C:C

35 z x y If light is moving out of the page (+x direction), and the electric field is in the +y direction, the magnetic field is in: A. +z direction. z direction C. +y direction D. none of the above

36 The diagram to the right shows a lens with some rays. How many of the below statements are true? This lens has positive focal length, f. The object distance, p, is positive. The image distance, q, is positive. The image is real. Object The magnification, M, is positive. The only way to see this image is to place your eye on the left side of the lens and look through the lens. A:2 :3 C:4 D:other

37 The sign of: f? p? q? A: positive : negative

38 The sign of: f? p? q? A: positive : negative F C

39 The sign of: f? p? q? A: positive : negative

40 air glass A glass air air glass C glass air D