Teaching Physics with the Physics Suite Edward F. Redish

Direction of magnetic forces

The figure at the left below shows a cross section of four long parallel wires (labeled A through D ) taken in a plane perpendicular to the wires. One or more of the wires may be carrying a current. If a wire carries a current it is in the direction indicated and has magnitude I0.

For each of the four vector quantities (i) through (iv) give the direction of the quantity. To indicate the direction, use one of the letters associated with a directional arrow on the "compass" figure at the right below. If the magnitude of the quantity is zero, write "0". If it is non-zero, but in none of the indicated directions, write "Other".

1. Only wires B and D are carrying current. The direction of the force on wire D is ____.
2. Only wires B and D are carrying current. The direction of the force felt by an electron traveling in the C direction (on the compass) is ____.
3. Only wires B and D are carrying current. The direction of the force felt by an electron traveling in the A direction (on the compass) is ____.
4. All four wires are carrying current. The direction of the net force felt by wire A is ____.

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