Question

4. Two straight wires are parallel and carry currents of 1.2 A in opposite directions, as shown. Find the direction of the magnetic field produced by the current in Wire 1 at the location of Wire 2 and mark the direction directly on your printed diagram using the direction symbols indicated. Label the symbol for the field direction B. Then find the direction of the magnetic force on Wire 2, mark it with the appropriate one of the direction symbols and label the force direction F. Finally, explain how your answer for the magnetic field and magnetic force would have changed if the current in Wire 1 had been reversed, but the current in Wire 2 remained the same, so that both currents were in the same direction.

Answer 1

The directions of magnetic force and magnetic field lines are shown in the figure.

The direction to find out the magnetic field lines is given by right hand curl rule. If the thumb shows the direction of current, then the curling fingers show the direction of magnetic field lines.

The direction of force can be given by right hand thumb rule, where

Thumb - Direction of magnetic field lines
Forefinger - Magnetic force
Centre finger - Current  

Such that forefinger, centre finger and thumb must be at 90 degrees to each other.