A discrete vector map has been constructed for the electric field in a plane that…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A discrete vector map has been constructed for the electric field in a plane that contains two unknown point charges fixed 4 cm apart on the horizontal axis. Selected vectors on the map have the following properties:
• At a point 1 cm to the right of the right-hand charge, the field vector has magnitude 90N/C and points directly to the right.
• At a point 1 cm to the left of the left-hand charge, the field vector has magnitude 30N/C and points directly to the left.
• Exactly midway between the two charges, the field is zero.
(a) Determine the sign of each charge and justify your answer using the directions of the measured field vectors.
(b) Using the magnitudes of the field vectors provided and the fact that the field at the midpoint is zero, calculate the ratio of the magnitudes of the two charges.
(c) Both charges are now increased to three times their original magnitudes while their signs remain unchanged. Quantitatively describe how each of the three field vectors listed in the stimulus would change (state new magnitudes and whether the directions would differ).
(d) Suppose instead that the signs of the original charges were reversed while their magnitudes stayed the same. Describe qualitatively how the overall pattern of the vector map would differ from the original map.