(a) If a current is passed in the rod from B to A, the rods get displaced. This displacement is caused by the force acting on the current carrying rod. The magnet exerts a force on the rod directed towards the left, with the result that the rod will get deflected to the left.
(b) No change is observed when the axis of the rod " AB " is moved and aligned parallel to the magnetic field and current is passed in the rod in the same direction. Since there is no force, so their will be no motion.
OR
Magnetic field is a vector quantity. A vector quantity is a quantity that has both magnitude and direction. It is typically represented by an arrow whose direction is the same as that of the quantity and whose length is proportional to the quantity's magnitude. The magnetic field has both direction and magnitude.
The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it. Therefore, it is taken by convention that the field lines emerge from the North Pole and merge at the South Pole. Inside the magnet, the direction of field lines is from its south pole to its north pole. The magnetic field lines are closed curves. They never cross one another. They all have the same strength. The density of the lines indicates the magnitude of the field. The magnetic field is stronger and crowded near the poles of a magnet. As we move away from the poles, it is weak, and the lines become less dense. Their density decreases with increasing distance from the poles.