Answer: μ0I/(4R).
- A μ0I/(2R)
- B μ0I/(4R)
- C μ0I/(2πR)
- D μ0I/(πR)
Correct answer: B. μ0I/(4R)
Explanation: For a full circular loop, B at the centre is μ0I/(2R); a semicircular arc contributes exactly half of this, giving μ0I/(4R).
The magnetic field around a long straight current-carrying wire forms concentric circles, with direction given by the right-hand rule (point thumb along I, fingers curl in the direction of B).
Concept context
Magnetic force on moving charges and currents, the Biot-Savart law, Ampere's law, and the cyclotron - how electric currents create and respond to magnetic fields.