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.
Field from potential
Charged particle released in a uniform field
Potential difference and work
Reading field lines
Field vs potential
Charge is conserved and quantized
Charge conservation and quantization
When gravity matters
Zero field with nonzero potential
Same voltage, same energy, different speeds
Capacitance of parallel plates
Acceleration of a charge in a field
Short answer 1. Define or explain: Coulomb versus Newton
3 ptsShort answer 2. Define or explain: Conductors vs insulators
3 ptsShort answer 3. Define or explain: Keep signs out of field magnitudes
3 ptsShort answer 4. Define or explain: Uniform field between parallel plates
3 ptsFree response
10 ptsTwo point charges are fixed on the x-axis. A charge of +Q is at the origin, and a charge of −Q is at x = d. Point P is located on the x-axis midway between them, at x = d/2.
A(i). Indicate the direction of the net electric field at point P. A(ii). Indicate the direction of the electric force that would be exerted on a small positive test charge placed at P.
B. Derive an expression for the magnitude of the net electric field at point P, in terms of Q, d and physical constants.
C. Derive an expression for the electric potential at point P, in terms of Q, d and physical constants.
D. A small charge +q is moved from point P to a point infinitely far from both charges. Determine the work done by the electric field during this displacement, and justify your answer.