When the conducting wire is moved parallel to magnetic lines of force then there is no induced current and no deflection in galvanometer. It is because the conducting wire does not cut the magnetic lines of force and so there is no change in magnetic flux linked with the circuit and no emf is induced.
When the conductor is perpendicular to the magnetic field, the force will be maximum. When it is parallel to the magnetic field, the force will be zero.
Force on a current-carrying wire that is parallel to magnetic field will be zero. This is because the magnitude of force depends on the sin of the angle between the direction of current and the direction of magnetic field, so if the current carrying wire is held parallel to the magnetic field, the force will be zero.Eventually, the strength of the magnetic field is strong where the lines are closer and they weaken as they closeness decreases. Hence, if the field lines in a magnetic field are parallel and equidistant, the magnetic field is uniform.
The official definition of the ampere is: One ampere of current through each of two parallel conductors of infinite length, separated by one meter in empty space free of other magnetic fields, causes a force of exactly 2 × 10−7 N/m on each conductor.
A larger current in the conductor will result in a larger force acting on it if the strength of the magnetic field is kept constant, as shown in Figure. The magnitude of the force on a current carrying conductor increases when the strength of the magnetic held is increased.