Electromagnetic Waves Lecture Notes

Introduction

• Topic: Electromagnetic Waves
• Focus: Combining electricity and magnetism into electromagnetic waves
• Class Environment: Light, air-conditioned, conducive for learning

Concepts to Understand

Interaction of Fields

• Changing magnetic field => Changes in the electric field
• Electromotive force (EMF) or voltage
• Fundamental idea: Electric and magnetic fields influence each other

Movement of Charges

• Example: Positive and negative charges moving up and down
• Effect on electric field (E-field)
• E-field Behavior: Oscillates up and down
• Graphing E-field over time: Oscillates between positive and negative values

Current and Magnetic Field

• Moving charges are analogous to current in a wire
• Current (I) leads to Magnetic Field (B): Right-hand rule application

Electromagnetic Waves

• Changing electric field (E) creates a magnetic field (B) and vice versa
• Representation: E-field and B-field oscillate at right angles to each other
• Nature: Transverse wave
• Propagation Speed: Speed of light (3 × 10^8 m/s)

Maxwell's Equations

• Combined electricity and magnetism
• Light as electromagnetic waves discovered by Maxwell
• Key points facilitated by the equations

Detection of Electromagnetic Waves

• Example: Car radio detecting radio waves
• Antenna: Collects radio waves; current oscillates in response to the electric field
• System Tuning: Using capacitors and inductors to match the resonant frequency

Electromagnetic Spectrum

• Components: Radio, Microwaves, Infrared, Visible, UV, X-rays, Gamma rays
• Relationships: Frequency and wavelength (c = f × λ)
• Applications: Understanding wavelengths of specific types such as radar, X-rays

Energy and Electromagnetic Waves

• Energy Calculation: For electromagnetic waves
• Electric and Magnetic Energy Density: 1/2 ε₀ E² and 1/2 μ₀ B²
• Intensity (S): Defined as power per area, calculated using energy density and speed of light

Practical Applications

• Calculating the total power output of the sun using intensity at Earth
• Example Problem: Burning ants by focusing sunlight using a lens

MisConceptual Questions and Problems

• Problems: Based on real-world applications of electromagnetic waves
• Example: Galaxy rotation and the Doppler shift analysis

Special Topics

Polarization

• Direction of the electric field (E-field)
• Types: Vertical and horizontal polarization
• Applications: Polarized sunglasses, 3-D movies

Radiation Pressure

• Concept: Electromagnetic waves exert pressure
• Absorbers vs. Reflectors: Different pressure calculations
• Practical Example: Solar sails – pushing spacecraft using sunlight

Summary and Final Thoughts

• Emphasis on connecting theoretical concepts with practical, real-world applications
• Homework problems designed to reinforce understanding of discussed concepts