12.3 Magnetism and Electromagnetic Induction

Magnetism and electromagnetic induction are key concepts in electricity and magnetism. They explain how magnetic fields interact with electric currents and vice versa. This relationship forms the basis for many modern technologies we use daily.

Understanding these principles helps us grasp how electric motors, generators, and transformers work. It also sheds light on the nature of electromagnetic waves, which are crucial for communication and various scientific applications.

Magnetism Fundamentals

Magnetic Fields and Poles

Top images from around the web for Magnetic Fields and Poles

• 

  Earth's magnetic field | Zappys Technology Solutions | Flickr View original

  Is this image relevant?

• 

  9.3 Earth’s Magnetic Field | Physical Geology View original

  Is this image relevant?

• 

  22.5 Force on a Moving Charge in a Magnetic Field: Examples and Applications – College Physics View original

  Is this image relevant?

• 

  Earth's magnetic field | Zappys Technology Solutions | Flickr View original

  Is this image relevant?

• 

  9.3 Earth’s Magnetic Field | Physical Geology View original

  Is this image relevant?

1 of 3

Top images from around the web for Magnetic Fields and Poles

• 

  Earth's magnetic field | Zappys Technology Solutions | Flickr View original

  Is this image relevant?

• 

  9.3 Earth’s Magnetic Field | Physical Geology View original

  Is this image relevant?

• 

  22.5 Force on a Moving Charge in a Magnetic Field: Examples and Applications – College Physics View original

  Is this image relevant?

• 

  Earth's magnetic field | Zappys Technology Solutions | Flickr View original

  Is this image relevant?

• 

  9.3 Earth’s Magnetic Field | Physical Geology View original

  Is this image relevant?

1 of 3

• Magnetic field surrounds magnets and magnetic materials, exerting forces on other magnets or magnetic materials
• Magnetic field lines represent the direction and strength of the magnetic field
  • Closer field lines indicate stronger magnetic field
  • Field lines always form closed loops, never intersecting
• Magnetic poles exist in pairs, north and south, always occurring together
  • Like poles repel, unlike poles attract
• Earth acts as a giant magnet with magnetic poles near geographic poles
  • Magnetic compass aligns with Earth's magnetic field, pointing approximately north-south

Electromagnets and Solenoids

• Electromagnets generate magnetic fields using electric current
  • Consist of a coil of wire wrapped around a ferromagnetic core (iron)
  • Magnetic field strength increases with more current or more coil turns
• Solenoid acts as a special type of electromagnet
  • Long, tightly wound coil of wire
  • Produces uniform magnetic field inside the coil when current flows
  • Magnetic field strength inside solenoid given by formula: $B = μ₀nI$
    • B: magnetic field strength
    • μ₀: permeability of free space
    • n: number of turns per unit length
    • I: current flowing through the solenoid
• Applications of electromagnets include electric motors, speakers, and MRI machines

Electromagnetic Induction

Faraday's Law and Induced Current

• Electromagnetic induction describes generation of electric current from changing magnetic field
• Faraday's law states induced electromotive force (EMF) in a closed loop equals negative rate of change of magnetic flux through the loop
  • Expressed mathematically as: $ε = -N(ΔΦ/Δt)$
    • ε: induced EMF
    • N: number of turns in the coil
    • ΔΦ: change in magnetic flux
    • Δt: time interval
• Induced current flows in a direction that opposes the change in magnetic field (Lenz's law)
  • Ensures conservation of energy in electromagnetic systems
• Factors affecting induced EMF include strength of magnetic field, area of loop, and rate of change of magnetic field

Generators and Transformers

• Generators convert mechanical energy into electrical energy using electromagnetic induction
  • Consist of a coil of wire rotating in a magnetic field
  • Alternating current (AC) generators produce sinusoidal voltage output
  • Direct current (DC) generators use commutators to produce constant polarity output
• Transformers transfer electrical energy between circuits with different voltages
  • Use electromagnetic induction to step up or step down AC voltage
  • Primary coil creates changing magnetic field in iron core
  • Secondary coil experiences induced EMF due to changing magnetic flux
  • Voltage ratio between primary and secondary coils proportional to turn ratio: $V_p/V_s = N_p/N_s$
    • V_p, V_s: primary and secondary voltages
    • N_p, N_s: number of turns in primary and secondary coils

Electromagnetic Spectrum

Properties and Types of Electromagnetic Waves

• Electromagnetic spectrum encompasses all types of electromagnetic radiation
• Consists of oscillating electric and magnetic fields perpendicular to each other and direction of propagation
• Classified by wavelength and frequency, ranging from long radio waves to short gamma rays
  • Radio waves: longest wavelength, lowest frequency (used in communication)
  • Microwaves: shorter wavelength (used in cooking, radar)
  • Infrared: associated with heat (thermal imaging)
  • Visible light: narrow band detectable by human eye
  • Ultraviolet: higher energy than visible light (causes sunburn)
  • X-rays: high energy, short wavelength (medical imaging)
  • Gamma rays: shortest wavelength, highest energy (emitted by radioactive decay)
• All electromagnetic waves travel at speed of light in vacuum (c ≈ 3 × 10⁸ m/s)
• Relationship between wavelength (λ), frequency (f), and speed of light (c): $c = λf$