Magnetic Lines of Force: Identifying the Incorrect Statement

This question requires identifying the statement about magnetic lines of force that is factually incorrect based on their properties.

Analyzing Magnetic Line Properties

• Statement 1: They attract each other while travelling in the same direction. This statement is NOT true. Parallel magnetic field lines travelling in the same direction exert a repulsive force on each other, not an attractive one. This is analogous to parallel currents.
• Statement 2: They behave like a stretched elastic string. This statement is conceptually considered true. This analogy helps explain the tendency of magnetic field lines to contract longitudinally, leading to attraction between opposite poles.
• Statement 3: They do not cross each other. This statement is true. Magnetic field lines form continuous loops and never intersect. If they did, it would imply multiple directions of the magnetic field at a single point, which is impossible.
• Statement 4: They can pass through all media. This statement is generally considered true. Magnetic field lines can penetrate all materials, although the field strength might be modified depending on the medium's magnetic permeability.

Conclusion on Incorrect Statement

Based on the properties of magnetic field lines, the statement that parallel lines travelling in the same direction attract each other is false. They actually repel.

Therefore, the statement that is NOT true is: They attract each other while travelling in the same direction.