A straight copper conductor is held parallel to the axis of a freely suspended magnetic needle such that the conductor is under the needle and the current is flowing from south to north. In which direction the north of magnetic needle will move?
When a current-carrying conductor is placed parallel to the axis of a magnetic needle, the magnetic field produced by the current interacts with the magnetic field of the needle. According to the right-hand rule, the direction of the force acting on the magnetic needle can be determined as follows:
1. Point your thumb in the direction of the current, from south to north (which is the direction defined in the question).
2. Extend your fingers in the direction of the magnetic field around the conductor. In this case, it will be in a circular pattern around the conductor.
3. The direction in which your fingers curl will indicate the direction in which the north end of the magnetic needle moves.
Applying the right-hand rule, it can be observed that the north end of the magnetic needle will move towards the east (perpendicular to the direction of the current flow).
To determine the direction in which the north end of the magnetic needle will move, we need to apply the right-hand rule for the magnetic field produced by a current-carrying conductor.
1. Extend your right hand and align your thumb in the direction of the current (from south to north in this case).
2. Curl your fingers around the conductor. The direction your fingers wrap around the conductor will indicate the direction of the magnetic field lines created by the current.
Now, if the magnetic field lines due to the current interact with the magnetic field of the needle, the needle will experience a force. According to the physics principle known as the right-hand rule for the force on a current-carrying conductor, the direction of the force can be determined:
1. Extend your right hand with your thumb pointing in the direction of the magnetic field created by the needle (from north to south in this case).
2. Align your fingers in the direction of the magnetic field created by the current-carrying conductor.
If the magnetic field due to the current and the magnetic field of the needle are in the same direction, the forces will be attractive and cause the north end of the needle to move closer to the conductor. If the fields are in opposite directions, the forces will be repulsive, and the north end will move away from the conductor.
So, to answer your question, if the current is flowing from south to north and the compass needle is freely suspended, the north end of the needle will move towards the copper conductor.