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First Name: Last Name: Student #: Instructor: Dr. K. Foyle Class: Physics 1BB3, Modern Physics for the Life Sciences

SECOND MIDTERM EXAMINATION DATE: March 12th, 2014 TIME: 7-9pm PLACE: T29 101 & 105 DURATION OF EXAMINATION: 2 Hour THIS EXAMINATION PAPER INCLUDES 14 PAGES AND 18 QUESTIONS. YOU ARE RESPONSIBLE FOR ENSURING THAT YOUR COPY OF THE PAPER IS COMPLETE. BRING ANY DISCREPANCY TO THE ATTENTION OF YOUR INVIGILATOR. Special Instructions:

Please write your name and student number on both this copy and the provided examination answer sheet, and please also pencil in your student number in the Student number box of the examination answer sheet.

Answer multiple-choice questions (questions 1 to 16) on the provided examination answer sheet.

Answer the written answer questions (questions 17 and 18) directly on this copy.

Return both your examination answer sheet and this copy at the end of the examination, after verifying your name and student number are written on both.

A calculator can be used if necessary.

A one-page formula sheet is provided on the back of this page, and a blank page has been attached at the end of this copy to use as scrap paper (pages 14).

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Mark: Multiple-choice questions (#1-16): /70 Written answer questions (#17-18): /30 Total: /100 ---------------------DO NOT WRITE ABOVE THIS LINE--------------------- FORMULA SHEET Useful data: Mass of the proton: mp=1.67*10-27 kg. Mass of the electron: me=9.11*10-31 kg. Fundamental unit of charge: e=1.60*10-19 C Permittivity constant: 0=8.85*10-12 C2/(N.m2) Permeability constant: 0=1.26*10-6 T.m/A Avogadros number: N=6.02 particles/mol Acceleration due to gravity: g=9.80 m/s2

1 ms = 10-3 s; 1 s = 10-6 s; 1 ns = 10-9 s Useful formulas: F=qq/(40r2) p=qr V=q/(40r) E=(Q/A)/0 |V|=|E|d =AI

F = q v

B

R=mv/(qB)

=

B

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Part 1: Multiple-choice questions (questions 1 to 16) Answer these questions on the provided examination answer sheet. Question 1: A positive charge is placed some distance away from a negative charge. If the positive charge is moved, how long does it take for the electric force exerted on the negative charge by the positive charge to respond and change direction and/or magnitude? A- No time at all, the response is instantaneous. B- Some finite amount of time that depends on the distance between the two charges. Question 2: Suppose a van der Graaf generator builds a positive static charge, and a grounded conductor is placed near enough to it so that a 8.0C amount of negative charge arcs from the conductor to the van der Graaf generator. Estimate the number of electrons that have been transferred from the conductor to the van der Graaf generator.

A- 1.110-18 B- 1.0 C- 8.0 D- 50 E- 5.01013

Question 3. The figure below shows two parallel plates that are 2.0 cm apart. The electric field between them is 6.7 x 104 N/C. An electron is launched at a 45o angle and with initial speed v0 from the positive plate. What is the maximum v0 such that the electron wont hit the negative plate?

A- 1.5 x 107 m/s B- 1.9 x 107 m/s C- 2.3 x 107 m/s D- 3.1 x 107 m/s E- 4.5 x 107 m/s

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Question 4. An electron is accelerated from rest by an electric field. After the acceleration, the electron is injected into a uniform magnetic field of 1.27 103 T. The velocity of the electron and the magnetic field lines are perpendicular to one another. The electron remains in the magnetic field for 5.00 ns. The angle between the initial electron velocity and the final electron velocity is

A- 1.1 rad

B - 5.8 102 rad

C - 8.68 102 rad

D - 6.5 102 rad

E- 2.3 rad

Question 5. A positively charged particle is moving through uniform fields E and B, which are directed in the positive x and positive y directions, respectively. If there is no resultant force on the particle, then its velocity is in the

A- positive x direction B- positive y direction C- positive z direction D- negative x direction E- negative z direction

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Question 6. Some forms of cancer can be treated using proton therapy in which proton beams are accelerated to high energies, then directed to collide into a tumor, killing the malignant cells. Suppose a proton accelerator is constituted of a tube 4.0 m long in which there is a constant electric field, and suppose the protons are accelerated to a speed 1.0x107 m/s. What is the value of the electric field in the proton accelerator (ignore any relativistic effects)?

A- 2.1 10-14 V/m B- 2.5 V/m C- 2.6 105 V/m D- 1.3 105 V/m E- 1.0 106 V/m Question 7. The intrinsic magnetic dipole moment of the electron has magnitude 9.3x10-24 A.m2. What is the maximum torque that can be exerted on an electron due to its intrinsic dipole moment in a 1.0 T magnetic field?

A- 9.3 10-24 N.m B- 1.9 10-22 N.m C- 5.8 10-5 N.m D- 9.3 N.m E- 0 N.m

Question 8. An electron moves from point i to point f , in the direction of a uniform electric field. During the displacement:

A- the work done by the field is positive and the potential energy of the electron-field system increases.

B- the work done by the field is negative and the potential energy of the electron-field system increases.

C- the work done by the field is positive and the potential energy of the electron-field system decreases.

D- the work done by the field is negative and the potential energy of the electron-field system decreases.

E- the work done by the field is positive and the potential energy of the electron-field system does not change.

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Question 9. A nC0.10 point charge and a nC0.20+ point charge are 15cm apart on the x-axis. The electric potential at the point on the x-axis where the electric field is zero is: A- 603 V B- 603 V C- 103 V D- 103 V E- 600 V Question 10. A proton moves in a constant electric field from point A to point B. The magnitude of the electric field is CN /102.4 4 and it is directed as shown in the figure, the direction opposite to the motion of the proton. If the distance from point A to point B is 0.18 m , what is the change in the protons electric potential energy, UA UB ? A- + 2.4 X 10 15 J B- + 1.2 X 10 15 J C- 1.2 X 10 15 J D- 2.4 X 10 15 J F- 1.8 X 10 15 J

Question 11. A particle with a charge C8105.5 is fixed at the origin. A particle with a charge of C8103.2 is moved from cmx 5.3= on the x-axis to y = 4.3 cm on the y-axis. The change in the potential energy of the two-particle system is: A- 3.1105 J B- 6.010 5 J C- 0 D- 6.010 5 J E- 3.110 5 J

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Question 12. A charged particle is launched with a velocity of 5.2 104 m/s at an angle of 35 with respect to a 0.0045-T magnetic field. If the magnetic field exerts a force of 0.0026 N on the particle, determine the magnitude of the charge on the particle. A- 19 C B- 15 C C- 11 C D- 23 C E- 27 C Question 13. Experimenter A uses a test charge 0q and experimenter B uses a test charge 02q to measure an electric field produced by stationary charges. A finds a field that is: A- the same in both magnitude and direction as the field found by B. B- greater in magnitude than the field found by B. C- opposite in direction to the field found by B. D- less in magnitude than the field found by B. E- either greater or less than the field found by B, depending on the acceleration of the test charge. Question 14. The figure below shows the electric field lines between two charged parallel metal plates. Which of the following statements is true? A- the upper plate is positive and the lower plate is negative. B- a proton at X would experience the same force if it were placed at Y. C- a proton at X would experience a greater force than if it were at Z. D- a proton at X would experience less force than if it were placed at Z. E- an electron at X could have its weight balanced by the electrical force.

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Question 15. Point charges q and Q are positioned as shown. If q = +2.0 nC, Q = -2.0 nC, a = 3.0 m, and b = 4.0 m, what is the electric potential difference, VA - VB?

A- 8.4 V B- 6.0 V C- 7.2 V D- 4.8 V E- 0 V Question 16. A charged particle is moving in a uniform, constant magnetic field. Which one of the following statements concerning the magnetic force exerted on the particle is false? A- The magnetic force does no work on the particle. B- The magnetic force increases the speed of the particle. C- The magnetic force changes the velocity of the particle. D- The magnetic force can act only on a particle in motion. E- The magnetic force does not change the kinetic energy of the particle.

---------------------End of Part 1: Multiple-Choice Questions------------------

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Part 2: Written answer questions (questions 16 and 17) Answer these questions directly on your examination copy. Make sure you answer all sub-questions. Explain clearly and concisely how you arrived to the answer. Part of your mark will be attributed based on the clarity of your explanations. A blank page is provided at the end of this copy (pages 14) for you to use as scrap paper. Question 16: An alpha particle (charge 2e, mass 6.68 x 10-27 kg) is shot directly toward a stationary uranium nucleus (charge 92e, R= 7.4 x 10-15 m), at a speed of 2.1 x 107 m/s.

(a) Will the alpha particle make contact with the nuclear surface? If not, how close will it get to the nucleus?

(b) What speed would the alpha particle need to just make contact with the nuclear surface?

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Question 17: The solar wind is a thin, hot gas given off by the sun. Charged particles in this gas enter the magnetic field of the earth and can experience a magnetic force. Suppose that a charged particle traveling with a speed of v = 9.0x103 m/s encounters the earths magnetic field at an altitude where the field has a magnitude B = 1.2x10-7 T, and that the particles velocity is perpendicular to the magnetic field. Also, consider that both the direction and the magnitude of the magnetic field remain constant along the trajectory of the particle. (a) Draw the trajectory of the particle in the case of a proton (indicate on your drawing the direction of the magnetic field). (b) Calculate the radius of the trajectory of the proton, R. (c) Calculate the cyclotron frequency, f, associated with the trajectory of the proton. (d) How would your answers to questions (a), (b) and (c) change if the particle were an electron instead of a proton?

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--------------------End of Part 2: Written Answer Question-------------------

-----------------------------END OF EXAMINATION-----------------------------

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