A pair of isolated point charges is arranged vertically in air
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Electric Force Field and Potential · Electric Force Field and Potential
Problem
A pair of isolated point charges is arranged vertically in air. A charge of +3q is fixed at the origin of a Cartesian coordinate system, and a charge of −q is fixed on the positive y-axis at y=8cm. Consider three off-axis points that all lie on the horizontal line y=4cm.
• Point D is at (x=−6cm,y=4cm).
• Point E is at (x=0,y=4cm).
• Point F is at (x=10cm,y=4cm).
A small positive test charge is hypothetically placed at each point to probe the local field.
(a) For each point (D, E, and F), indicate the quadrant-style compass direction (e.g., upward and leftward, purely rightward, etc.) of the net electric field vector.
(b) Rank the magnitudes of the net electric field at points D, E, and F from greatest to least. Clearly justify any ties.
(c) Describe qualitatively how the field pattern along the entire horizontal line y=4cm would change if the upper charge were changed from −q to +q while all other quantities remain fixed.