Electric Force, Field, and Potential unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1 Paper 2 Paper 3

Each paper is built from this unit’s 47 terms and is the same for everyone, so a teacher can assign “Unit 2, Paper 3” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.

Suggested time 35 min 32 points0/17 attempted

Why a charged rod attracts neutral paper

Electric field

Charge concentrates at sharp points

Electroscope behavior

The classic midpoint result

Why equipotentials are perpendicular to field lines

Coulomb's law

Electric potential

Charge in a uniform field is a projectile problem

Conduction versus induction versus polarization

Superposition of fields

Electron-volt as an energy

Short answer 1. Define or explain: When gravity matters

3 pts

Short answer 2. Define or explain: Acceleration of a charge in a field

3 pts

Short answer 3. Define or explain: Charge is conserved and quantized

3 pts

Short answer 4. Define or explain: Fields add as vectors, potentials as scalars

3 pts

Free response

8 pts

QUALITATIVE/QUANTITATIVE TRANSLATION (Question 4, 8 points). Equipotential lines for a region with an electric field are shown: from left to right they are labeled −3V0, −2V0, −V0, 0, +V0, and +2V0, with the +x-direction pointing right. Point S lies on the −2V0 equipotential and Point T on the +V0 equipotential. A small sphere (not shown) with positive charge +Q has initial speed vS in the +x-direction and kinetic energy KS at Point S. It moves to Point T, with the electric force the only force acting. At T it has speed vT and kinetic energy KT. For C: a new sphere of the same mass but negative charge −Q starts at S with the same initial speed vS in the +x-direction, again with only the electric force acting, and has kinetic energy Knew at T.

A. Indicate whether vT is greater than, less than, or equal to vS, and justify with conceptual reasoning beyond algebraic solutions.

B. Derive an expression for KT in terms of V0, Q, KS, and physical constants, as appropriate.

C. Indicate whether Knew is greater than, less than, or equal to KT, and briefly justify by referencing your derivation in part B.