Superposition of magnetic fields from perpendicular currents

Steps:

• Apply right-hand rule to first wire: thumb in current direction, fingers curl to show circular B-field around wire.
• Apply right-hand rule to second wire: perpendicular current yields B-field circling oppositely at intersection.
• Vector-add B-fields at compass location: fields from both wires point in same direction, combining to north along that line.
• Plotting compass needle aligns with net B-field, pointing north in direction of resultant.

Why C is correct:

• C shows needle aligning with net B-field from superposition, per Biot-Savart law for straight wires.

Why the others are wrong:

• A: Ignores second wire's field, showing only one wire's influence.
• B: Reverses direction, misapplying right-hand rule to one current.
• D: Assumes opposing fields canceling, but currents' orientations add fields.

Final answer: C