Two point charges move side by side with equal speeds along parallel straight lines…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges move side by side with equal speeds v along parallel straight lines that are a distance d apart. The charges are located at the same x coordinate and move in the +x direction.
• Charge 1 has value +q and is on the line y=+2d.
• Charge 2 has value −q and is on the line y=−2d.
Consider Point O at the origin (x=0,y=0,z=0), which lies exactly midway between the two lines of motion at the instant when both charges are at x=0.
(1) Part 1: State the direction of the magnetic field at Point O due to Charge 1 alone. Explain your reasoning clearly.
(2) Part 2: State the direction of the magnetic field at Point O due to Charge 2 alone. Explain any similarities or differences relative to your answer for Charge 1.
(3) Part 3: Determine the direction and qualitative magnitude (zero, non-zero finite, or indeterminate without calculation) of the net magnetic field at Point O when both charges are present simultaneously. Provide a detailed justification using superposition principles.
(4) Part 4: If the speed of the negative charge were doubled while the positive charge’s speed remained v, describe how the direction and magnitude of the net magnetic field at Point O would change. Explain your reasoning.
(5) Part 5: Discuss qualitatively how all of your answers would differ if the two charges moved in opposite directions along their respective lines instead of in the same direction.