Concept of a magnetic field — common mistakes

Always pay close attention to the angles given in exam questions. For the force formula $F = BIL \sin(\theta)$, θ is the angle between the wire and the field. For the flux formula $\Phi = BA \cos(\theta)$, θ is the angle between the normal to the area and the field. Confusing these two is a very common mistake!

Magnetic flux density (B) measures the strength of the magnetic field at a specific point, essentially how 'dense' the field lines are. Its unit is the Tesla (T). Magnetic flux (Φ), on the other hand, measures the total amount of magnetic field passing through a given area. Its unit is the Weber (Wb).

Iron is a ferromagnetic material, meaning it can be easily magnetised. When placed inside a current-carrying solenoid, the iron core becomes strongly magnetised itself. Its own magnetic field aligns with and adds to the solenoid's field, significantly increasing the overall magnetic flux density.

Yes, under static conditions. A stationary electric charge creates an electric field but no magnetic field. A steady current (charges moving at a constant velocity) creates a magnetic field. However, a changing electric field can induce a magnetic field, and a changing magnetic field can induce an electric field – this dynamic interplay is the foundation of electromagnetism and light waves.

The 'normal' is an imaginary line drawn perpendicular to the surface of the area. When calculating magnetic flux with the formula Φ = BA cos(θ), the angle θ is always measured from this normal line to the direction of the magnetic field lines.