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PHYSICS, M4 EQ-Bank 6 MC

Two long, straight, parallel conductors are placed 3.0 cm apart and carry equal currents of 20 A in opposite directions. Which of the following best describes the magnetic field at the midpoint between the two wires?

  1. The magnetic field is zero because the wires carry equal and opposite currents.
  2. The magnetic field at the midpoint is caused only by one of the wires, since the other field is canceled out by symmetry.
  3. The magnetic fields due to each wire are in the same direction and add, resulting in a non-zero net field.
  4. The magnetic field at the midpoint is directed along the wires due to symmetry.
Show Answers Only

\(C\)

Show Worked Solution
  • Use the right-hand grip rule, put your thumb in the direction of the current, and the fingers show magnetic field direction around wire.
  • At the midpoint the left wire’s (e.g., current up) field is into the page and the right wire’s (current down) field is also into the page
  • So both fields at the midpoint are in the same direction therefore they add together so the magnetic field at the midpoint is non-zero.

\(\Rightarrow C\)