In the topic of magnets and magnetic fields, how are magnetic field line models helpful?

• A. They allow the exact magnetic field magnitude at every point to be determined without any measurements or calculations.
• B. They demonstrate that magnetic monopoles exist at the ends of a bar magnet because field lines start at one end and terminate at the other.
• C. They show the actual physical paths that individual charged particles must follow in a magnetic field, regardless of the particle’s velocity.
• D. They provide a visual way to represent the direction of the magnetic field and the relative field strength, with denser lines indicating stronger fields.

Answer: (D)