I need help
In studying the cross section of a straight current carrying wire, you notice that the magnetic
field lines run counter-clockwise. What is the direction of the current in the wire and how do you
know?
2. You are looking into a current carrying solenoid and notice that the compass needle indicates
that you are at the South end of the magnetic field. What is the direction of the current in the coil
and how do you know?
To determine the direction of the current in the wire or coil, you can use the right-hand rule, which relates the direction of the magnetic field to the direction of the current.
1. For the straight current carrying wire with counter-clockwise magnetic field lines (as viewed from above):
- Grasp the wire with your right hand, with your thumb pointing in the direction of the current.
- If the magnetic field lines are running counter-clockwise, the direction of your curled fingers in your right hand would correspond to the direction of the magnetic field.
Therefore, the direction of the current in the wire is also counter-clockwise, as the magnetic field is generated by the current.
2. For the current carrying solenoid where the compass needle indicates the South end of the magnetic field:
- Hold the solenoid in your right hand with your fingers wrapped around it in the direction of the current flow (clockwise or counter-clockwise).
- Your thumb would then point towards the North end of the magnet.
If the compass needle indicates the South end of the magnetic field, it means the North-seeking pole of the compass is attracted towards the solenoid. According to the right-hand rule, this attraction happens when the current flows in a counter-clockwise direction when viewed from behind the solenoid.
Therefore, the direction of the current in the solenoid is counter-clockwise.