Magnetic field from four current-carrying wires · BPhO 2009 #8
Physics · electromagnetism
Problem
An electric current flowing through a wire produces a magnetic field around the wire. Four wires carrying identical currents are shown placed at the corners of a square. The symbol ⊗ indicates a current flowing along the wire into the page, and the symbol ⊙ indicates a current flowing along the wire pointing out of the page. In which of the diagrams is the magnetic field at the centre of the square greatest?
A. [⊙ ⊙] [⊙ ⊙]
B. [⊙ ⊗] [⊗ ⊙]
C. [⊙ ⊙] [⊗ ⊗]
D. [⊗ ⊙] [⊗ ⊙]