T

Electro magnetism

Learning Outcomes

  • Understand the fundamental principles of the relationship between magnetism and electricity.

Assessment Criteria

  • 5.1 Describe the effects of magnetism (attraction and repulsion).

  • 5.2 State the difference between magnetic flux and flux density.

Electro-magnetism

Magnetic Field

  • The area around a magnet or electromagnet where magnetic force effects can be felt.

  • Represented by unseen lines of flux that form closed loops.

Key Conventions:

  • Lines of flux cannot cross.

  • Lines of flux flow from the north pole to the south pole.

Behavior of Permanent Magnets

  • North to North Poles: Like poles repel.

  • North to South Poles: Unlike poles attract.

Relationship Between Electricity and Magnetism

  • An electrical current flowing through a conductor produces a magnetic field.

Current Direction Convention:

  • Flowing into the Conductor: Away from the observer.

  • Flowing out of the Conductor: Towards the observer.

Direction of Magnetic Fields

  • Maxwell’s Screw Rule: Establishes the direction of magnetic fields around conductors.

    • Imagine driving a screw in the direction of current flow; this shows the magnetic field direction.

Magnetic Fields due to Electric Current

  • Straight Conductors: Produce a magnetic field.

  • Flat Coil: Produces a magnetic effect.

  • Solenoid: A tightly wound coil producing a magnetic field similar to a bar magnet, containing distinct north and south poles.

Function of Solenoids:

  • Create controlled magnetic fields used in electromagnets.

  • Commonly used in relays, allowing circuit control by low-power signals.

Key Quantities in Magnetism

Magnetic Flux

  • The number of magnetic lines of force in a magnetic circuit.

  • Comparable to electric current in a circuit; measured in webers (Wb) and denoted by Φ.

Magnetic Flux Density

  • Indicates the compaction of magnetic flux lines.

  • Calculated as:

    • ( 𝛽 = ∅ / 𝐴 )

    • Where:

      • 𝛽: magnetic flux density in teslas (T).

      • ( ∅ ): magnetic flux in webers (Wb).

      • ( A ): cross-sectional area in square meters (m²).