Lecture Notes on Magnetism and Electromagnetism

Properties of Magnets

• Poles: Every magnet has two poles: North and South.
• Magnetic Forces: Strongest at the poles;
  • Unlike poles attract.
  • Like poles repel.

Magnetic Materials

• Magnetic Materials: Attracted and can be magnetized (contains iron, nickel, or cobalt).
  • Examples: Steel (mainly iron).
• Types of Magnetic Materials:
  • Hard Magnetic Materials (e.g., Steel): Difficult to magnetize, retain magnetism (used for permanent magnets).
  • Soft Magnetic Materials (e.g., Iron): Easy to magnetize, lose magnetism easily (used in electromagnets and transformers).
• Non-Magnetic Materials: Not attracted/repelled by magnets, includes metals without iron, nickel, or cobalt, and all non-metals.

Testing for Magnetic Properties

• Bring material close to a known magnet:
  • Repelled: Magnet.
  • Attracted: Magnetic Material.
  • No effect: Non-Magnetic Material.

Magnetization of Magnetic Materials

• Induced Magnetism: Induced by a strong magnet; usually weak.
• Methods:
  1. Stroking with a Magnet: Stroke in one direction to induce stronger magnetism.
  2. Using Direct Current (DC): Coil of wire with DC creates a magnetic field that magnetizes the core.

Demagnetization of Magnets

• Methods:
  1. Heating the magnet.
  2. Hitting it with a hammer.
  3. Using an alternating current (AC).

Magnetic Fields

• Definition: Region where magnetic materials experience a force.
• Field Lines: Represent direction and strength; run from North to South, never cross.
• Strength: Closer lines indicate stronger fields.
• Earth’s Magnetic Field: Earth's core (iron/nickel) creates its magnetic field; compass needles align with it.

Electromagnetic Induction

• Definition: EMF induced when a conductor interacts with a changing magnetic field.
• Current Direction: Can be reversed by:
  • Reversing wire motion.
  • Reversing magnetic field direction.
• Max Induced Current: When moving perpendicular to the magnetic field.

Fleming's Right-Hand Rule

• Usage: To determine the direction of induced current.
  • Thumb: Motion.
  • Index: Magnetic field direction.
  • Middle: Current direction.

Electromagnetic Induction in Solenoids

• Induced Current: Changes based on the speed of magnet movement and number of turns in the solenoid.
• Lenz's Law: Induced current opposes the change in magnetic field.

AC Generators

• Function: Converts kinetic energy into electrical energy; based on electromagnetic induction.
• Slip Rings: Allow alternating current by reversing current direction every half turn.

Magnetic Field Around Conducting Wire

• Formation: When current flows, a circular magnetic field is produced.
• Direction: Determined by the Right-Hand Grip Rule.

Electromagnet and Applications

• Electromagnet: Solenoid with an iron core; used in various applications (e.g., electric relays, bells).

Force on Current-Carrying Conductors

• Force Direction: Determined by Fleming's Left-Hand Rule.

Loudspeakers and Headphones

• Operation Principle: Convert electrical signals into sound using coil movement in magnetic fields.

Mutual Induction & Transformers

• Transformer Components: Primary coil, secondary coil, iron core.
• Types: Step-up (increases voltage) and step-down (decreases voltage).
• Application in National Grid: High voltage transmission minimizes energy loss.

Final Remarks

• Importance of High Voltage Transmission: Reduces current in wires, minimizing heat losses.
• Power Loss Calculations: Illustrate efficiency gains through high voltage and low current transmission.

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Candidates are expected to have a thorough understanding of the syllabus details outlined in the accompanying figure.