Magnetism

Magnets (Chapter 22 Notes)

Everyday Uses of Magnets

  • Magnets are integral in various everyday applications. Some brainstormed uses include:

    • Refrigerators (fridge magnets)

    • Credit cards (magnetic strips)

    • Magnetic north compasses

    • Magnetic fasteners in purses and bags

    • Magnetic tools for easy retrieval of dropped metallic items

Behavior of Magnets

  • Magnet Structure

    • Every magnet has two poles: North (N) and South (S).

    • Like poles repel each other, while opposite poles attract.

    • Magnetic poles cannot be isolated.

  • Magnetic Fields

    • Caused by moving charges (electric current).

    • Measurement units:

    • Tesla (T) or Gauss (1 T = 10^4 Gauss = 1 N A/m)

    • Examples of magnetic fields:

      • Fridge magnet: ~50 Gauss = 5 x 10^{-3} T

      • Earth’s magnetic field: ~0.5 Gauss = 5 x 10^{-5} T

      • Superconducting magnets: ~400,000 Gauss = 40 T

Electric and Magnetic Forces

  • Non-charged objects, like an uncharged pith ball, will not respond when placed near a charged rod.

  • The interaction of magnets with charges:

    • North side of a magnet attracts a south charge.

    • South side of a magnet does not affect neutral objects.

  • Summary Observations:

    • N and S poles of the magnet should not be confused with positive and negative electric charges.

Magnetic Field Lines

  • Detection of Magnetic Fields:

    • Located using test magnets or compass.

    • Normal convention: Field lines emanate from the North and enter the South pole.

    • Density of lines indicates strength.

  • Test Equipments:

    • Iron filings can visually represent magnetic field lines.

    • Compasses are often used due to their reliability in detecting field vectors.

Earth's Magnetic Field

  • The geographic and magnetic poles are not perfectly aligned.

  • The Earth's magnetic field originates from moving charges in the Earth's core.

  • Magnetic field influences navigational patterns for various animals (e.g., birds).

  • The Earth's magnetic field has reversed multiple times throughout history.

Magnetic Forces in Motion

  • Effects on Charged Particles:

    • Magnetic fields impact moving charges, exerting forces.

    • A static charge is unaffected by magnetic fields.

  • Creating Magnetic Fields:

    • Generated by bar magnets, current-carrying wires (straight and loops).

Electrical Motors & Solenoids

  • Motors turn electrical energy into kinetic energy, commonly used in everyday appliances.

  • Solenoids: Combination of loops of wire creates a strong and uniform magnetic field inside.

  • Magnetic Strength Calculation:

    • For a solenoid:

    • Magnetic Field, B = \mu_0 n I

    • where $n$ = turns per unit length, $I$ = current.

Different Types of Magnets

  • Ferromagnetism: Permanent moments align even without an external field (e.g., iron, nickel).

  • Paramagnetism: Random orientations align under an external field (e.g., paper clips).

  • Diamagnetism: No permanent moments, exhibiting a slight repulsion toward magnetic fields (e.g., copper).

Magnetic Field of Current-Carrying Wires

  • The strength of magnetic fields generated by current-carrying wires follows:

    • B = \frac{\mu_0 I}{2 \pi r}

    • with $B$ being field strength, $140 * {n}) = \pi\mathrm{

Force on Charged Particles

  • When a charge moves through a magnetic field, it experiences a force given by:

    • F = q v B \sin{\theta}

    • For perpendicular movement of charge to field lines, \theta = 90^\circ results in maximal force.

Applications and Implications

  • Aurorae: Interaction between cosmic rays and Earth's magnetic field results in spectacular displays at the poles.

  • Current in Circular Orbits: Centripetal forces relate to charge mass, charge, velocity, and field strength; thus various applications such as particle accelerators and mass spectrometers.

Conclusion

  • This chapter covers the principles of magnets, including types, forces on charged particles, effects of magnetic fields on currents, and practical applications. The properties of magnetic fields and their applications in technology help to drive the functionality of devices in our daily lives.