Overview
This lecture explains the relationship between wavelength and frequency of electromagnetic waves, distinguishes the regions of the electromagnetic spectrum, and demonstrates how to use the basic wave equation for problem-solving.
Wavelength and Frequency Relationship
- Wavelength is the distance between two consecutive crests or troughs of a wave, measured in meters.
- Frequency is the number of waves passing a point per second, measured in hertz (Hz).
- Wavelength and frequency are inversely proportional: as frequency increases, wavelength decreases, and vice versa.
Electromagnetic Spectrum Regions
- The electromagnetic spectrum consists of waves with varying frequencies and wavelengths.
- Main regions (from longest wavelength/lowest frequency to shortest/highest): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
- Radio waves have the longest wavelengths; gamma rays have the shortest.
- Gamma rays have the highest frequency and photon energy; radio waves have the lowest.
Uses and Characteristics of Spectrum Regions
- Radio waves: broadcasting; wavelength 1 cm to 1000 m; size of football fields.
- Microwaves: cooking, radar, signals; wavelength 0.1 mm to 1 cm; size of a penny.
- Infrared: perceived as heat; used in thermal scanners.
- Visible light: detected by human eyes; wavelength 400-700 nm; size of a virus.
- Ultraviolet: comes from the sun; wavelength 10⁻⁸ to 10⁻¹⁰ m; size of water molecules.
- X-rays: used in medical imaging; wavelength 10⁻¹⁰ to 10⁻¹² m; size of atoms.
- Gamma rays: medical use (cancer treatment); wavelength ~10⁻¹² m; size of atomic nuclei.
The Basic Wave Equation
- The basic wave equation: v = f λ, where v is speed (m/s), f is frequency (Hz), and λ is wavelength (m).
- In a vacuum, the speed of light (v) is 3 × 10⁸ m/s.
- To find wavelength: λ = v / f.
- To find frequency: f = v / λ.
Example Problems
- Calculating wavelength: For f = 6 × 10¹⁴ Hz, λ = 3 × 10⁸ m/s ÷ 6 × 10¹⁴ Hz = 5 × 10⁻⁷ m.
- Calculating frequency: For λ = 20 m, f = 3 × 10⁸ m/s ÷ 20 m = 1.5 × 10⁷ Hz.
Wave Behavior in Different Media
- In materials other than vacuum, electromagnetic waves slow down.
- Frequency remains the same in a new medium, but speed and wavelength decrease.
Key Terms & Definitions
- Wavelength (λ) — Distance between two consecutive wave crests/troughs.
- Frequency (f) — Number of waves passing a point per second (Hz).
- Photon — Packet of electromagnetic wave energy.
- Electromagnetic Spectrum — Range of all electromagnetic wave frequencies and wavelengths.
- Wave Equation — v = f λ, relates speed, frequency, and wavelength.
Action Items / Next Steps
- Complete the reflection log: What happens to wavelength if frequency increases?
- Arrange electromagnetic waves in order of increasing wavelength and frequency.
- Solve: What is the frequency of a microwave with wavelength 1.5 × 10² m?
- Prepare for Module 2: Practical Applications of Electromagnetic Waves.