Module 5
1. Module 5
1.7. Page 5
Module 5—Wave Theory of Light
Lesson Summary
In this lesson you focused on the following questions:
- Is electromagnetic radiation more than just visible light?
- How is the electromagnetic spectrum organized?
- How are electrical charge and magnetic field related to the production of electromagnetic radiation?
- How are electromagnetic waves generated, transmitted, and received in technologies such as the radio?
A rainbow is a natural example of the visible light spectrum. It is organized by wavelength and frequency and illustrates all of the colours that, taken together, form white light. Visible light, however, represents only a small portion of the entire electromagnetic radiation spectrum, which is organized by wavelength and frequency. Low frequency, low-energy EMR includes AC power, radio waves, microwaves, and infrared heat. High frequency, high-energy EMR includes ultraviolet waves, X-rays, gamma rays, and cosmic rays, which can permanently damage biological systems.
In 1865, James Clerk Maxwell predicted that perpendicular, oscillating, electric, and magnetic fields propagated in the form of an electromagnetic wave. He added that an electromagnetic wave is produced whenever a charge is accelerated. And if the electric charge exhibits simple harmonic motion, the frequency of the wave matches the frequency of the simple harmonic motion. Maxwell also concluded that all electromagnetic waves travel through a vacuum at a common speed and obey the universal wave equation. Furthermore, the waves exhibit similar properties to that of transverse waves: interfering, diffracting, refracting, and reflecting.
In 1887, Heinrich Hertz experimentally verified Maxwell’s predictions by using a spark gap to produce a 109-Hz wave that was received by a nearby antenna. Radio technology uses accelerating charges in a similar way to produce EMR waves that propagate outwards from a transmitter tower. The EMR waves are capable of inducing a current in a distant conducting antenna. Furthermore, the sine wave produced at the transmitter tower is identical to the sine wave of the induced current in the receiving antenna, facilitating the delivery and reproduction of sounds, music, and voices.
Lesson Glossary
electromagnetic spectrum: a general classification of all electromagnetic radiation based on wavelength, frequency, and energy
frequency: the number of cycles per unit of time (Hz = 1 cycle/second)
wavelength: the distance between adjacent points on a wave that vibrate in phase with one another (m)