In-Depth Notes on Invisible Light

Chapter 9 - Invisible Light

• Electromagnetic Spectrum

  • The electromagnetic spectrum (EMS) encompasses all forms of electromagnetic radiation, which vary in wavelength and frequency.

  • Major components of the EMS include:

  • Radio Waves

    • Applications: AM (Amplitude Modulation) and FM (Frequency Modulation) radio broadcasting.

    • Radar technology for detection and ranging.

  • Microwaves

    • Used for heating food - specifically by causing water molecules to rotate.

    • Applications also include terahertz detectors used in various technologies.

  • Infrared Radiation

    • Wavelengths between 700 nm (red end of the visible spectrum) and 1 mm.

    • Source of thermal radiation emitted by objects at or near room temperature.

    • Related principles include blackbody radiation and its dependence on temperature.

    • Applications: Weather satellites, infrared cameras, and military technologies such as Stinger missiles.

  • Ultraviolet Rays (UV)

    • Types:

    • UVA - Causes skin aging; found in tanning beds.

    • UVB - Causes sunburn and immune system damage.

    • UVC - Most dangerous but absorbed by the ozone layer.

    • UV rays can damage cellular structures.

  • X-rays

    • Range of wavelengths between 0.01 to 10 nanometers.

    • Effective for medical imaging due to bone absorption.

    • Techniques: Backscatter X-ray technology for security purposes, and imaging such as CAT and MRI scans for enhanced detail.

  • Gamma Rays

    • Extremely high frequency and energy; biologically hazardous as ionizing radiation.

    • Typically produced via atomic decay processes and can be lethal at high exposure levels.

Key Concepts

• Blackbody Radiation

  • Electromagnetic radiation emitted by a body in thermal equilibrium, which depends solely on the temperature of the body.

  • Example of calculating temperature using the wavelength: T = 3.0 x 10^6 nm K / λ.

• Radiated Power

  • Formula: P = σAT⁴ where σ is the Stefan-Boltzmann constant (5.68 x 10^-8 W m^2 K⁴).

  • Example calculation for solar power output based on the sun's temperature and surface area.

Applications of Electromagnetic Radiation

• Infrared Cameras

  • Similar to regular cameras but operate in longer wavelengths beyond visible light (up to 14,000 nm).

• PET Scans

  • Use positrons for imaging functional processes in the body and to help diagnose cancers, as cancer cells consume more glucose.

• Ultrasound Technology

  • Operates at frequencies above human hearing (~20 kHz); used in medical imaging and various technological applications.

Summary of Penetration through Earth and Atmosphere

• Various forms of radiation have unique penetration capabilities through Earth’s atmosphere, with wavelengths determining their susceptibility to absorption and scattering.

Key Measurements in the EMS

• Wavelength and Frequency

  • The frequency (Hz) and corresponding wavelengths (meters) of different types of electromagnetic radiation can range significantly, influencing their applications and effects.