Electromagnetic Spectrum Overview

The Electromagnetic Spectrum

• Radio waves are used for communication systems, which creates interference with astrophysical signals, and medical equipment like MRI scans.
• MRI (magnetic resonance imaging) uses radio waves to create detailed images of organs and tissues.
  • High frequency radio waves are tuned to resonate with specific nuclei in the body.
  • Sensitivity to the magnetic field allows for detailed imaging down to the millimeter level.
  • Radio waves used in MRI scans are considered safe.
• Microwaves are high-frequency radio waves with short wavelengths.
  • Used for satellite communication, long-distance land-based transmissions, and radar.
    • Microwaves are useful in these applications because they can travel at high speeds and carry large amounts of information.
    • Microwaves require a clear line of sight between transmitter and receiver.
  • Produced by atoms and molecules through thermal agitation.
• Extremely Low Frequency (ELF) radio waves are used to communicate with submerged submarines.
  • ELF radio waves can penetrate salt water due to their long wavelengths.
• AM radio uses amplitude modulation to place information on radio waves.
  • Audio signals are modulated to shift the amplitude of the carrier wave.
  • Receivers tuned to the carrier wave receive audio information and reject other frequencies.
• FM radio uses frequency modulation to carry information on higher frequencies.
  • Carrier waves are modulated in frequency by audio signals.
  • FM radio is less susceptible to noise than AM radio because noise affects the amplitude of AM waves.
• Television is broadcast using electromagnetic waves.
  • VHF (very high frequency) and UHF (ultra high frequency) radio waves are used for TV broadcasting
  • Each TV channel requires a large range of frequencies due to the visual and audio information it carries.
  • TV video signals are transmitted using AM, while audio signals are transmitted using FM.

Relationship between Frequency, Wavelength, Wavespeed

• Wave speed is a constant value for all electromagnetic waves.
• The formula 𝑐 = 𝑓𝜆 provides the relationship between frequency (f), wavelength (λ), and the speed of light (c).

Rules of Thumb for Electromagnetic Waves

• Higher-frequency waves are more energetic and have greater penetrating power.
• Higher-frequency waves can carry more information per unit time.
• The shorter the wavelength, the finer the detail that can be resolved.

Transmission, Reflection, and Absorption

• When electromagnetic waves interact with materials, they can be transmitted, reflected, or absorbed.
• Transparency: When a material allows waves to pass through easily.
• Opacity: When a material blocks waves from passing through.
• Absorption: When a material interacts with the waves, causing the material to heat up.
• Transparency and opacity can be frequency dependent.

Radio Waves

• The broad category of radio waves encompass any electromagnetic wave produced by electric currents.
• Include microwaves, AM/FM radio signals, cellular signals, and TV signals.
• Radio waves used in astrophysical studies are produced by natural phenomena, not by "alien radio stations."
• Extremely low frequency (ELF) radio waves (50-60 Hz) produced by power lines are a source of power transmission loss.

Electromagnetic Waves

• Electromagnetic waves are produced by oscillating electric and magnetic fields.
• The speed of light is calculated as c = 1 / (𝜇𝑜 𝜀𝑜) = 3 x 10⁸ m/s.
• Maxwell predicted that light is an electromagnetic wave.
• Hertz confirmed the existence of electromagnetic waves in the lab and verified their speed of light.
• The relationship between the wave characteristics is described by the equation 𝑣𝑤 = 𝑓𝜆, where 𝑣𝑤 is the propagation speed of the wave, f is the frequency, and 𝜆 is the wavelength.
• For all electromagnetic waves, 𝑐 = 𝑓𝜆.
• Electromagnetic waves have several rules of thumb:
  • High-frequency waves are more energetic and penetrating.
  • High-frequency waves carry more information per unit time.
  • Shorter wavelengths allow for resolving smaller details.
• When an electromagnetic wave impinges on a material, it can be transmitted, reflected, or absorbed.
• Transparency and opacity are frequency dependent.

Radio and TV Waves

• Radio waves are produced by currents in wires and circuits.
• They are divided into subcategories, including microwaves, AM, FM, cellular telephones, and TV.
• Low-frequency radio waves (6000 km wavelength) are produced by high-voltage AC power transmission lines.
• Extremely low frequency (ELF) radio waves are used to communicate with submerged submarines.
• AM radio waves (540-1600 kHz) are used for commercial radio signals and are amplitude modulated.
• FM radio waves (88-108 MHz) are used for commercial radio signals and are frequency modulated.
• Television broadcasting utilizes both VHF (54-88 MHz, 174-222 MHz) and UHF (470-1000 MHz) frequencies.
• TV video signal is AM, while the TV audio is FM.

Ultraviolet Light

• Ozone depletion is attributed to the breakdown of ozone molecules by chlorofluorocarbons (CFCs).
• UV radiation has benefits:
  • Vitamin D production in the skin.
  • Treatment of infantile jaundice and skin conditions.
  • Sterilizing workspaces and tools, killing germs.
  • Analytical tool for identifying substances through fluorescence.
  • Used in special microscopes to detect smaller details.

X-Rays

• X-rays are a high-frequency electromagnetic radiation.
• They are used for imaging objects opaque to visible light, such as the human body.
• X-ray penetration depends on density, providing detailed density information.
• They are used in radiology for medical diagnostics.
• X-ray diffraction is used to detect the shape of molecules and the structure of crystals.
• X-ray induced fluorescence is used for trace-metal analysis.

Gamma Rays

• Gamma rays (γ rays) are the most penetrating nuclear radiation.
• They are emitted by nuclei during natural decay or induced nuclear processes.
• Gamma rays are more penetrating and damaging to living tissue than X-rays.
• They have applications in cancer therapy, sterilization, and medical imaging.
• The long-term hazards of consuming radiation-preserved food are unknown and controversial.

Detecting Electromagnetic Waves from Space

• The entire electromagnetic spectrum is used for space research.
• Penzias and Wilson detected background radiation from the Big Bang.
• Radio telescopes are used to detect radio waves.

Explore the electromagnetic spectrum, focusing on radio waves and their applications in communication systems and MRI technology. Learn how microwaves facilitate satellite communication and radar, and understand their properties and uses in various fields. This quiz will deepen your knowledge of electromagnetic wave applications in science and technology.