Multiple Choice Problems (2 Points Each): Please Select the Best Answer for Each Question

AP Physics C Magnetism Test

Name: ______

Multiple Choice Problems (2 points each): Please select the best answer for each question.

1.An electron moves in the negative x direction, 4.A proton (charge e), traveling perpendicular to through a uniform magnetic field in the a magnetic field, experiences the same force negative y direction. The magnetic force on as an alpha particle (charge 2e) which is also the electron is: traveling perpendicular to the same field. The ratio of their speeds, vproton/valpha is: A) 0.5 B) 1 C) 2 D) 4 E) 8

5.At one instant an electron is moving in the positive x direction along the x axis in a A) in the negative x direction region where there is a uniform magnetic B) in the positive y direction field in the positive z direction. When C) in the negative y direction viewed from a point on the positive z axis, it D) in the positive z direction subsequent motion is: E) in the negative z direction A) straight ahead B) counterclockwise around a circle in 2.The direction of the magnetic field in a certain the xy plane region of space is determined by firing a test C) clockwise around a circle in the xy charge into the region with its velocity in plane various directions in different trials. The D) in the positive z direction field direction is: E) in the negative z direction A) one of the directions of the velocity when the magnetic force is zero B) the direction of the velocity when the magnetic force is a maximum C) the direction of the magnetic force D) perpendicular to the velocity when the magnetic force is zero E) none of the above

3.A magnetic field CANNOT: A) exert a force on a charge B) accelerate a charge C) change the momentum of a charge D) change the kinetic energy of a charge E) exist

6.A uniform magnetic field is directed into the 7.An electron and a proton each travel with equal page. A charged particle, moving in the speeds around circular orbits in the same plane of the page, follows a clockwise spiral uniform magnetic field, as shown in the of decreasing radius as shown. A reasonable diagram (not to scale). The field is into the explanation is: page on the diagram. Because the electron is less massive than the proton and because the electron is negatively charged and the proton is positively charged:

A) the charge is positive and slowing down B) the charge is negative and slowing A) the electron travels clockwise down around the smaller circle and the C) the charge is positive and speeding proton travels counterclockwise up around the larger circle. D) the charge is negative and speeding B) the electron travels up counterclockwise around the E) none of the above smaller circle and the proton travels clockwise around the larger circle C) the electron travels clockwise around the larger circle and the proton travels counterclockwise around the smaller circle D) the electron travels counterclockwise around the larger circle and the proton travels clockwise around the smaller circle E) the electron travels counterclockwise around the smaller circle and the proton travels counterclockwise around the larger circle

8.An electron is traveling in the positive x direction. A uniform electric field E is in 11. The diagram shows a straight wire carrying the negative y direction. If a uniform a flow of electrons into the page. The wire magnetic field with the appropriate is between the poles of a permanent magnet. magnitude and direction also exists in the The direction of the magnetic force exerted region, the total force on the electron will be on the wire is: zero. The appropriate direction for the magnetic field is:

F)  G)  A) ← B) → C) into the page A) the positive y direction B) the negative y direction C) into the page 8.The diagram show a straight wire carrying D) out of the page current i in a uniform magnetic field. The E) the negative x direction magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. 9.The current is from left to right in the Of the following possibilities, the direction conductor shown. The magnetic field is into of the magnetic field is: the page and point S is at a higher potential than point T. The charge carriers are:

A) to the right B) opposite the direction of F A) positive C) in the direction of F B) negative D) into the page C) neutral E) out of the page D) absent E) moving near the speed of light 9.A current is clockwise around the outside edge 10. In a certain mass spectrograph, an ion beam of this page and a uniform magnetic field is passes through a velocity filter consisting of directed parallel to the page, from left to mutually perpendicular fields E and B. The right. If the magnetic force is the only force beam then enters a region of another acting on the page, the page will turn so the magnetic field B' perpendicular to the right edge: beam. The radius of curvature of the A) moves toward you resulting ion beam is proportional to: B) moves away from you A) EB'/B C) moves to your right B) EB/B' D) moves to your left C) BB'/E E) does not move D) B/EB' E) E/BB'

10. The magnetic torque exerted on a flat 11. The diagrams show five possible current-carrying loop of wire by a uniform orientations of a magnetic dipole μ in a magnetic field B is: uniform magnetic field B. For which of F) maximum when the plane of the these does the magnetic torque on the dipole loop is perpendicular to B have the greatest magnitude? G) maximum when the plane of the loop is parallel to B H) dependent on the shape of the loop for a fixed loop area I) independent of the orientation of the loop A) I J) such as to rotate the loop around B) II the magnetic field lines C) III D) IV E) V

Short Answer Problems (5 points each): Solve the following problems. Use the five steps discussed in class to ensure maximum credit.

12. An electron (charge = –1.6 × 10–19 C) is moving at 3 × 105 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is: Given Unknown Equation Plug In Solution

13. At one instant an electron (charge = –1.6 × 10–19 C) is moving in the xy plane, the components of 5 5 its velocity being vx = 5 × 10 m/s and vy = 3 × 10 m/s. A magnetic field of 0.8 T is in the positive z direction. At that instant the magnitude of the magnetic force on the electron is: Given Unknown Equation Plug In Solution

14. A proton is in a region where a uniform electric field of 5 × 104 V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be: Given Unknown Equation Plug In Solution

15. Electrons (mass m, charge –e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field B that is perpendicular to their velocity. The radius of the resulting electron trajectory is: Given Unknown Equation Plug In Solution

16. A 2 meter wire caries a .02 amp current through a magnetic field of .5 T at an angle of 20o to a line perpendicular to the wire. What is the force on the wire? Given Unknown Equation Plug In Solution

17. A current of 3.0 A is clockwise around the outside edge of this page, which has an area of 5.8 × 10–2 m2. The magnetic dipole moment is: Given Unknown Equation Plug In Solution

18. An electron is launched with velocity v in a uniform magnetic field B. The angle θ between v and B is between 0 and 90o. As a result, the electron follows a helix, its velocity vector v returning to its initial value in terms of the constants given and any fundamental constants in a time interval of: Given Unknown Equation Plug In Solution

Free Response Problems (15 points): Please neatly answer the following question on a separate sheet of paper.

1984E1. An electron from a hot filament in a cathode ray tube is accelerated through a potential difference ε. It then passes into a region of uniform magnetic field B. directed into the page as shown above. The mass of the electron is m and the charge has magnitude e. a. Find the potential difference a necessary to give the electron a speed v as it enters the magnetic field. b. On the diagram above, sketch the path of the electron in the magnetic field. c. In terms of mass m, speed v, charge e, and field strength B, develop an expression for r, the radius of the circular path of the electron. d. An electric field E is now established in the same region as the magnetic field, so that the electron passes through the region undeflected. i. Determine the magnitude of E. ii. Indicate the direction of E on the diagram above.