PracticeQuiz3Y

Page 1: Exam Instructions

• Instructor: Brian Shotwell, Department of Physics, University of California, San Diego

• Course: Physics 2B (Electricity and Magnetism), Spring 2023

Directions for the Quiz

• Must have the correct test form (A-D) as indicated on the seating assignment chart.

• Incorrect quiz may invalidate the entire exam.

• Submit the exam in the designated pile after ripping off page 2 for answers.

Quiz Structure

• Multiple-choice questions: 5 questions

• Free-response question: 1 question with multiple parts

• Answers are to be recorded on the last sheet.

Important Procedural Notes

• Provide NAME, UCSD PID number, and SEAT/CHAIR on each sheet:

  • Example: Name, A12345678, “J13”

• Must show all work for every problem—even multiple-choice.

• Answers to MC questions go on page 2; all work shown may assist in academic integrity cases.

• Box final answers for fill-in-the-blank questions, noting significant figures.

• Partial credit available for work demonstrated.

Calculator and Materials

• Allowed calculator must not have:

  • Keypad

  • Internet access

  • Smartphones are not permitted.

• One 8.5x11” cheat sheet (both sides) and one sheet of blank paper for scratch work are allowed.

Conduct During Exam

• No communication with others during the exam.

  • This includes speaking, looking at others' work, or outside help.

• If you need to leave the room:

  • Call a proctor to assist

  • Proctor will take your exam and smartphone

  • Ensure all work is concealed on the desk.

Numerical Constants

• Fundamental constants relevant for the questions:

  • e = 1.602 x 10^(-19) C

  • k = 8.99 x 10^9 N·m^2/C^2

  • ε0 = 8.85 x 10^(-12) C^2/(N·m^2)

  • μ0 = 4π x 10^(-7) T·m/A

  • me = 9.11 x 10^(-31) kg

  • mp = mn = 1.67 x 10^(-27) kg

Page 2: Quiz Formulas

Quizzes 1-2 Summary of Key Formulas

• Force Between Charges:

  • F12 = k|q1 * q2| / r^2

• Electric Field:

  • E = kq / r^2

  • Edipole (far away) = 2k / r^3 * p

• Electric Flux:

  • Φe = ∫ E · dA = Q_enc / ε0

• Potential Energy and Work:

  • U = -p · E

  • E_mech = K + U

  • δV = -∫_fi E · ds

Quizzes 3-4 Summary of Key Formulas

• Work:

  • W = ∫_fi F·ds

• Capacitance:

  • C = ε0 * A/d

  • C_eq = C1 + C2 (parallel), or 1/C_eq = 1/C1 + 1/C2 (series)

Page 3: Multiple Choice Questions

1. Gaussian surface to prove E_plane = η / (2ε0) nˆ

   • Valid choices: A) Solid Sphere B) Spherical Shell C) Solid Cylinder D) Cylindrical Shell (Walls) E) Cylindrical Shell (Endcaps) F) None

2. Charge on outer surface of conductor B when central particle is charged, net flux given, options provided.

3. Assembling four protons at corners of a square, determine energy value A based on AkQ^2/L formula.

4. Using Gaussian surface (cylindrical) with a positive point charge at the origin—options regarding applicability of Gauss's Law.

5. Ranking electric fields produced by four uniformly charged spheres at equal distances from the center—options provided.

Page 4: Continued Multiple Choice Questions

• Q5 involves ranking the spheres according to electric field magnitudes at point P, based on given relationships.

Page 5: Free Response (10 points)

Free Response Parts

• Part (a): Electric potential at the surface of a metal sphere with a specified net charge.

• Part (b): Create and label equipotential surfaces around the sphere.

Escape Speed (c)

• Calculate escape speed for an electron resting on the surface of a charged metal sphere.