Properties of electromagnetic waves

Course Details

Field of Study: Electronics Engineering
Course Name: Optoelectronics
Description: Electromagnetic waves share six properties with all forms of wave motion

The six properties of electromagnetic waves are the following

  • Polarization
  • Reflection
  • Refraction
  • Diffraction
  • Interference
  • Superposition

Polarization
From the previous post we have discussed the direction of light’s propagation and its associated electric and magnetic fields. Polarization arises from the direction of the E-field vector with respect to the direction of the light’s propagation. Since a light wave’s electric field vibrates in a direction perpendicular to its propagation motion, it is called a transverse wave and is polarizable. A sound wave, by contrast, vibrates back and forth along its propagation direction and thus is not polarizable.
Light is unpolarized if it is composed of vibrations in many different directions, with no preferred orientation as shown in figure (a) below. Many light sources (e.g., incandescent bulbs, arc lamps, the sun) produce unpolarized light. Vertically polarized light is shown in Figure (b) and horizontally polarized light in Figure (c). Each is an example of linearly polarized light. Figure (d) shows linearly polarized light making an angle of θ with the vertical. In this case, the tilted E-vector can be described by its components, Ex and Ey.

unpolarizedpolarizedhorizontal-polirizedlinearly-polirized

Reflection
When a ray of light reflects off a surface (such as a mirror), its new direction depends on only the angle of incidence. The law of reflection states that the angle of incidence on a reflecting basic surface is equal to the angle of reflection.
reflection
The law of reflection states that the angle of incidence (θi) is equal to the angle of reflection (θr).

Refraction
When a ray of light passes from one medium to another, it changes direction (bends) at the interface because of the difference in speed of the wave in the media. The ratio of this speed difference is called the index of refraction (n). The ratio of the indices of refraction and the direction of the two rays of light for the two media are expressed in Snell’s law as shown below in Figure and Equation. where n1 and n2 are the indices of refraction for the two media
θ is the angle of incidence
φ is the angle of refraction.
refraction

Diffraction
Diffraction is the bending of a wave as it passes through a hole or around an obstacle.
If light consists of parallel rays, they would travel through a small pinhole and make a small, bright spot on a nearby screen.
Diffraction is proportional to the ratio of wavelength to width of gap.

Interference and Superposition
Waves can interact and combine with each other, resulting in a composite form.
Interference is the interaction of the two waves.
– reinforcing interaction = constructive interference
– canceling interaction = destructive interference
Superposition is the method used to model the composite form of the resulting wave.
Constructive interference occurs when two wave motions reinforce each other, resulting in a wave of greater amplitude.
constructive
Destructive interference occurs when two waves exactly cancel, so that no net motion remains.
destructive

Share this article:
Previous Post: Concept of light waves

October 27, 2014 - In Academics, Electronics

Next Post: What is LASER?

October 28, 2014 - In Academics, Electronics

Related Posts

Leave a Reply

Your email address will not be published.