Electric 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.
Potential inside a conducting sphere
Equipotential surfaces
Potential energy of a charge pair
Potential from a graph of E vs x
Field and potential can be independently zero
Potential energy of a charge configuration
Potential of a charged conductor
Why field is the negative gradient
Sign of the potential integral
Work and potential difference
Electric potential of a point charge
Energy of assembling charges
Short answer 1. Define or explain: Field from a graph of V vs x
3 ptsShort answer 2. Define or explain: Why potential is easier than field
3 ptsShort answer 3. Define or explain: Electron volt
3 ptsShort answer 4. Define or explain: Potential inside a uniformly charged insulating sphere
3 ptsFree response
10 ptsThis course has no free-response prompt tagged to this unit, so one from elsewhere in the course is used. It is still worth writing — the skill transfers.
Two long horizontal frictionless rails a distance L = 0.40 m apart lie in a uniform vertical magnetic field of magnitude B = 0.50 T. A conducting rod of mass m = 0.20 kg lies across the rails, and the circuit is completed by a resistor R = 2.0 Ω. The rod is given an initial speed v₀ = 6.0 m/s along the rails and then released.
Determine the initial emf and the initial current, and state the direction of the magnetic force on the rod.
Determine the initial magnitude of the rod’s acceleration.
Write the differential equation governing v(t) and show that v(t) = v₀e^(−t/τ) is its solution, identifying τ.
Evaluate τ and the speed at t = 5.0 s.
Determine the total energy dissipated in the resistor and the total distance the rod travels, and explain why the rod never quite stops in finite time.