🔖 Topics

  • Properties of electromagnetic waves
  • Electromagnetic spectrum
  • Dipole antennae
  • Speed of light
  • Index of refraction

🎯 Objectives

  • Calculate some of the basic properties of electromagnetic waves including wavelength, frequency, and wavenumber
  • Describe the motion of waves emitted from a dipole antenna
  • Calculate the speed of light in a material

📋 Sequence

  • General properties of waves
    • Sinusoidal oscillations
    • Frequency and period
    • Angular frequency and wave number
    • Amplitude
    • \( v = f \lambda \)
    • Transverse versus longitudinal waves
  • Properties of electromagnetic waves
    • The amplitudes of the electric and magnetic fields are related by \( E = cB \)
    • EM waves are transverse waves
    • Electric and magnetic fields travel at the speed of light
    • Yet another RHR! You can figure out the direction of propagation using a RHR.
  • Speed of light in a medium
    • Speed of light in a vacuum is constant - \( 3 \times 10^8 \: m/s \)
    • The index of refraction is defined as \( n = c / v \) or \( v = c / n \)
    • Frequency does not change as you move from one medium to another
    • Wavelength does change: \( c / n = f \lambda_{new} \Rightarrow \lambda_{new} = \lambda / n \)
    • Index of refraction is usually a function of frequency, leading to dispersion

🖥️ Animations, Simulations, Activities

📝 Practice Problems

  1. What is the wavelength of radio waves broadcast by an FM radio station with a frequency of 90.9 MHz?
  2. Approximately how long does it take sunlight to travel from the Sun to Earth? The average Sun to Earth distance is about 150 million kilometers.
  3. The speed of light in topaz is \( 1.85 \times 10^8 \: m/s \). What is the index of refraction of topaz?
  4. Light with a wavelength of 692 nm in vacuum passes into window glass with an index of refraction of 1.52. What is the wavelength and frequency of light inside the glass?

✅ Partial Solutions

  1. 3.3 meters
  2. \( 500 \: s \approx 8.3 \: min \)
  3. 1.62
  4. \( \lambda = 455 \: nm \), \( f = 4.34 \times 10^{14} \: Hz \)

📘 Connected Resources

  • Animations for Physics and Astronomy. Longitudinal and Transverse Waves. February 2012.
  • Friends Physics. ELECTROMAGNETIC WAVE | PHYSICS ANIMATIONS AND SIMULATIONS | INTERACTIVE ANIMATIONS. February 2022.
  • Giambattista, Alan, et al. College Physics With an Integrated Approach to Forces and Kinematics. 5th ed., McGraw-Hill Education, 2020.
  • Lesics. Understanding Electromagnetic Radiation! | ICT #5. September 2019.