Overview
This lecture introduces electromagnetic waves (EM waves), their properties, the electromagnetic spectrum, and the differences between ionizing and non-ionizing radiation.
Electromagnetic Waves Basics
- Electromagnetic (EM) waves are disturbances that transfer energy and do not require a medium to travel.
- EM waves can move through solids, liquids, gases, and even a vacuum.
- Mechanical waves (like sound or water waves) require a medium to propagate.
- EM waves are produced when an electric field interacts with a magnetic field, both being perpendicular to each other and to the wave's direction.
- All EM waves travel at a constant speed of (3.0 \times 10^8) m/s in a vacuum.
Wave Properties and Equations
- Amplitude is the height of a wave and relates to its energy.
- Wavelength is the distance between two consecutive crests or troughs, measured in meters.
- Frequency is the number of wave cycles per second, measured in hertz (Hz).
- The wave speed equation: speed = frequency × wavelength ((v = f \lambda)).
- As wavelength increases, frequency decreases, and vice versa (inverse relationship).
The Electromagnetic Spectrum
- The electromagnetic spectrum arranges EM waves by increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light (red to violet), ultraviolet, x-rays, gamma rays.
- As you move from radio waves to gamma rays, frequency increases and wavelength decreases.
- Visible light colors are ordered by frequency: red (lowest) to violet (highest).
Photons and Energy
- EM waves can be described as streams of photons (energy particles).
- The energy of a photon is directly proportional to the frequency of the wave.
- Higher frequency EM waves (like x-rays, gamma rays) have more energetic photons.
Ionizing vs. Non-Ionizing Radiation
- Ionizing radiation (x-rays, gamma rays) has enough energy to remove electrons from atoms (more dangerous).
- Non-ionizing radiation (radio, microwaves, infrared, visible, ultraviolet) does not have sufficient energy to ionize atoms.
Key Terms & Definitions
- Electromagnetic Wave (EM wave) — wave formed by oscillating electric and magnetic fields, traveling through space.
- Wavelength — distance between two consecutive wave crests or troughs.
- Frequency — number of wave cycles passing a point per second.
- Photon — massless particle carrying energy as electromagnetic radiation.
- Ionizing Radiation — EM waves with energy high enough to ionize atoms (x-rays, gamma rays).
- Non-ionizing Radiation — EM waves with insufficient energy to ionize atoms (radio, microwaves, etc.).
- Electromagnetic Spectrum — the range of all EM wave frequencies and wavelengths.
Action Items / Next Steps
- Draw and label the electromagnetic spectrum from radio waves (longest wavelength) to gamma rays (shortest wavelength).
- Review the wave speed equation and practice solving for frequency, wavelength, or speed.
- Prepare for further discussion on the effects of ionizing vs. non-ionizing radiation in the next lesson.