A student draws electric field lines for a system of two isolated point charges kept…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Electric Force Field and Potential · Electric Force Field and Potential
Problem
A student draws electric field lines for a system of two isolated point charges kept 6cm apart on an air table. Exactly 12 lines emanate radially outward from charge A and all of them terminate on charge B; no field line starts or ends anywhere else. The pattern is perfectly symmetric about the line joining the charges.
(i) From the field-line information, identify the sign of each charge and compare the magnitudes ∣A∣ and ∣B∣. Give reason for your answer.
(ii) Explain why no field line begins or ends anywhere other than on the two charges. What does this observation tell you about the algebraic sum A+B?
(iii) Without using any numerical calculation, state whether the magnitude of the electric field at the midpoint of the line joining the two charges is zero or non-zero. Justify your answer on the basis of the field-line pattern.