The method and the results are on the electric field lab. Do the analysis yourself first, then check the answers below.
Quick answer: An electric field is the region around a charge where other charges feel a force, with strength is E = F / q in N/C. These answers go with the Physics 11-12 lab on electric field: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
The sample readings lie close to a straight line from 0 V to 6 V over 10 cm. The answers below use the gradient of 0.60 V/cm and show how it relates to E = V / d, which you should also check for your own set of readings.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.2
The points lie on a straight line through the origin, so V increases linearly with distance and the field between the electrodes is uniform.
Question 2 Gradient
Gradient = ΔV / Δx = (6.00 − 0.00) / (10 − 0) = 0.60 V/cm = 60 V/m. (A least-squares fit of the six points gives 0.599 V/cm.)
Question 3 Field strength
E = −dV/dx has magnitude 60 V/m. The field points in the direction of falling potential, from the 6.0 V electrode towards the 0 V electrode.
Question 4 Force on a charge
F = qE = 2.0 × 10⁻⁹ × 60 = 1.2 × 10⁻⁷ N, in the direction of the field for a positive charge.
Question 5 Predicted gradient
E = V / d = 6.0 / 0.100 = 60 V/m. The measured value 60 V/m agrees with the prediction within the reading error of the voltmeter.
Question 6 Second line
Points at the same x have the same potential, so lines of constant x are equipotentials. They are perpendicular to the field, which points along the length of the paper.
Question 7 Near the edges
The paper has a finite width, so current paths can bulge outwards and the field lines curve (edge effects). The field is uniform only well inside the edges.
Question 8 Better readings
Use a voltmeter with high resistance so it does not disturb the circuit; use a finer scale for x; take readings at more points; ensure good contact between the paper and the electrodes; repeat and average each reading. Any two sensible points.
