6.2.2 Properties of Electromagnetic Waves

Electromagnetic waves can be absorbed, transmitted, refracted, or reflected in ways that vary with wavelength. In this lesson, we will explore the effects of absorption, transmission, refraction, and reflection, focusing on the velocity differences in different substances.

Absorption, Transmission, Refraction, and Reflection (HT only)

Absorption:

• Absorption occurs when a substance absorbs and dissipates the energy carried by electromagnetic waves, converting it into other forms of energy (e.g., heat).
• Different substances have varying degrees of absorption for different wavelengths of electromagnetic waves.

Transmission:

• Transmission refers to the ability of a substance to allow electromagnetic waves to pass through it without significant absorption or reflection.
• Transparent materials, such as glass and air, exhibit high transmission for certain wavelengths.

Refraction:

• Refraction is the bending of electromagnetic waves as they pass from one medium to another with a different refractive index.
• The change in direction occurs due to the difference in the velocity of the waves in different substances.

Reflection:

• Reflection occurs when electromagnetic waves encounter a boundary and bounce back, reversing their direction.
• The extent of reflection depends on the properties of the materials and the angle of incidence.

Constructing Ray Diagrams for Refraction

Ray diagrams are graphical representations used to illustrate the refraction of waves at the boundary between two different media.

To construct a ray diagram:

1. Draw a line perpendicular to the boundary at the point of incidence.
2. Draw the incident ray (incoming wave) at an angle relative to the perpendicular line.
3. Apply the law of refraction (Snell's law) to determine the angle of refraction (bent ray) based on the refractive indices of the media.

Using Wave Front Diagrams to Explain Refraction (HT only)

Wave front diagrams illustrate the shape and position of wave fronts, which are surfaces of constant phase of the wave.

When a wave travels from one medium to a different medium, its speed changes, leading to a change in the shape and orientation of the wave front. The change in wave speed causes the wave front to bend, resulting in refraction.

Refraction can be explained in terms of the change of speed that occurs when a wave travels from one medium to another.

• When a wave enters a medium with a higher refractive index, it slows down, causing the wave front to bend towards the normal (perpendicular) line.
• When a wave enters a medium with a lower refractive index, it speeds up, causing the wave front to bend away from the normal line.

Conclusion

Understanding the properties of electromagnetic waves and their interaction with different substances provides insights into the behaviour of waves. Absorption, transmission, refraction, and reflection are phenomena that vary with wavelength and depend on the velocity differences in different mediums. Constructing ray diagrams and wave front diagrams allows us to visually represent the refraction of waves at boundaries between different media.