When a current-carrying conductor is placed in a magnetic field, it experiences a force. This force is known as the magnetic force and is given by the formula F = BIL, where F is the magnetic force, B is the magnetic field strength, I is the current flowing through the conductor, and L is the length of the conductor that is perpendicular to the magnetic field.


The direction of the magnetic force is given by the right-hand rule. If the thumb of the right hand is pointed in the direction of the current, and the fingers are pointed in the direction of the magnetic field, then the palm of the hand will point in the direction of the magnetic force. The direction of the magnetic force is always perpendicular to both the current and the magnetic field.


When the conductor is parallel to the magnetic field, the angle between the current and the magnetic field is 0°. In this case, the magnetic force is also 0. This can be seen from the formula F = BIL. Since the angle between the current and the magnetic field is 0°, the sine of the angle is 0, and therefore the magnetic force is 0.


When the conductor is placed in a magnetic field at an angle other than 0° or 90°, the magnetic force will have a component that is perpendicular to the conductor and a component that is parallel to the conductor. The perpendicular component will cause the conductor to move in a circular path, while the parallel component will have no effect on the conductor. When the conductor is parallel to the magnetic field, the parallel component of the magnetic force is 0, and therefore there is no resultant force acting on the conductor.


In conclusion, when a current-carrying conductor is placed parallel to a magnetic field, it experiences no magnetic force because the angle between the current and the magnetic field is 0°, resulting in a sine of 0. This means that there is no resultant force acting on the conductor.

According to Fleming's Left Hand Rule, the thumb, forefinger and the middle finger are in such a way that they are perpendicular to each other, so the thumb indicates the force, the forefinger indicates the direction of the magnetic field and the middle finger indicates the flow of current.Hence, if the current carrying conductor is parallel to the magnetic field, then they do not follow the rule which is the reason why no force acts on it.