Overview
This lecture covers the electromagnetic spectrum, explaining the properties, order, sources, and interactions of different types of electromagnetic waves.
Properties of Electromagnetic Waves
- Electromagnetic (EM) waves are transverse waves that oscillate perpendicular to the direction of energy transfer.
- In a vacuum, all EM waves travel at a speed of (3 \times 10^8) meters per second.
- In other mediums, EM waves can travel at different speeds, leading to refraction (direction change).
The Electromagnetic Spectrum
- The EM spectrum is divided into seven basic types, forming one continuous range.
- Types include (from longest to shortest wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.
- Wavelength and frequency are inversely related; as wavelength increases, frequency decreases.
- Radio waves have the largest wavelength and smallest frequency, while gamma rays have the smallest wavelength and largest frequency.
- Wavelengths range from kilometers (radio waves) to less than a thousandth of a nanometer (gamma rays).
- Human eyes detect only a small section called visible light.
Visible Light and Spectrum Order
- Visible light contains the colors red, orange, yellow, green, blue, indigo, and violet ("ROY G. BIV").
- After violet is ultraviolet; before red is infrared.
- Ultraviolet, x-rays, and gamma rays are ionizing and can damage cells.
- Microwaves and radio waves, used in communication, are on the far left of the spectrum.
Sources and Interactions of Electromagnetic Waves
- EM waves originate from various sources: gamma rays from radioactive decay; visible, ultraviolet, and x-rays from electron transitions; infrared from molecular vibrations.
- EM waves can be reflected, absorbed, transmitted, or a combination when interacting with matter.
Key Terms & Definitions
- Electromagnetic (EM) Wave — A transverse wave that transfers energy through oscillating electric and magnetic fields.
- Transverse Wave — A wave where oscillations occur perpendicular to energy transfer.
- Refraction — The change in direction of a wave due to a change in medium.
- Ionizing Radiation — EM waves (ultraviolet, x-ray, gamma) that can remove electrons from atoms, causing cellular damage.
Action Items / Next Steps
- Memorize the order of electromagnetic waves, starting from visible light and moving outward.
- Learn the colors of visible light using the mnemonic "ROY G. BIV."