Magnetism and Electromagnetism Study Guide

Key Concepts of Magnetism

  • Magnet: Has North & South Poles with a surrounding magnetic field.

  • Magnetic Variation: Difference between Earth's rotational axis (geographic poles) & magnetic poles. The angle between directions to true North and Magnetic North is known as the Angle of Magnetic Deviation.

Magnetic Field

  • Definition: The area surrounding a magnet where magnetic forces can be detected.

  • Properties:

    • Produced by moving electric charges.

    • The direction of the magnetic field is determined by the direction of current flow.

    • The magnetic field is strongest at the poles.

  • Field Lines:

    • Lines point from North (N) to South (S).

    • Draw magnetic field lines with arrows showing the direction of the field.

Compass

  • Definition: A tiny bar magnet that is free to rotate.

  • Function: The north pole of a compass points toward the Geographic North Pole, which is near the Magnetic South Pole.

  • Alignment: Compass needles align with magnetic field lines, indicating directions.

Electromagnetism

Electromagnet

  • Definition: A current-carrying wire coiled around an iron core that produces a magnetic field.

Electromagnetic Induction

  • Concept: Inducing current by changing the magnetic field in a conductor.

    • Example: Moving a magnet across a wire generates a current.

Transformers

  • Definition: Devices that change voltage through electromagnetic induction.

  • Types:

    • Step-Up Transformer: Increases voltage by increasing the number of coils.

    • Step-Down Transformer: Decreases voltage by decreasing the number of coils.

  • Calculation:

    • For a step-up transformer:

    • Example Calculation: Input Voltage = 10V AC; Output Voltage = 20V (using coils).

Generators and Motors

Generator

  • Converts mechanical energy into electrical energy.

    • Energy Sources: Nuclear, gas, steam, coal, wind, water.

Motor

  • Converts electrical energy into mechanical energy by rotating a coil in a magnetic field.

Strengthening Electromagnets

Three Methods:

  1. Increase the number of coils.

  2. Increase the current.

  3. Use a more conductive or larger core material.

Magnet Types

Temporary Magnets

  • Easily magnetized and unmagnetized.

    • Example: Electromagnets.

Permanent Magnets

  • Difficult to magnetize and unmagnetize.

    • Properties: Stay magnetized longer.

    • Example: Alnico materials.

Magnetic Domains

  • Definition: Regions within a magnet where the electrons' spins are aligned.

Transformer Problems

  • Example: To calculate the load current and load voltage in a step-down transformer:

    • Given: 2390 turns on primary, 28 turns on secondary, and load resistance of 350 Ω.

    • Voltage Calculation: $V2 = \frac{V1}{(Np/Ns)}$.

    • Load Voltage Calculation: $V = I \times R$.