Light and the electromagnetic spectrum Study Guide

Light interacts with different materials in several ways, leading to phenomena like reflection, refraction, and total internal reflection (TIR). These interactions are fundamental to how we perceive the world and are crucial for technologies such as fiber optics and lenses.

Reflection occurs when light bounces off a surface. The law of reflection states that the angle of incidence (the angle between the incoming ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal). Both the incident ray, the reflected ray, and the normal lie in the same plane.

Refraction is the bending of light as it passes from one medium to another, such as from air to water. This bending occurs because light changes speed as it enters a different medium. The extent of bending depends on the refractive indices of the two media and the angle of incidence. The ray diagram for refraction shows the light ray bending towards the normal when entering a denser medium and away from the normal when entering a less dense medium.

Total Internal Reflection (TIR) is a special case of refraction where light, attempting to pass from a denser medium to a less dense medium, is completely reflected back into the denser medium. This happens when the angle of incidence in the denser medium exceeds a specific value called the critical angle. For TIR to occur, two conditions must be met: light must be travelling from a denser to a less dense medium, and the angle of incidence must be greater than the critical angle. Ray diagrams for TIR show the incident ray striking the boundary and being reflected back into the original medium, obeying the law of reflection.

Electromagnetic radiation, which includes a range of waves from radio waves to gamma rays, has diverse applications across various aspects of modern life. Each type of radiation possesses unique properties, such as wavelength and frequency, that make it suitable for specific uses. For instance, long-wavelength radio waves are ideal for broadcasting and communication over large distances due to their ability to diffract around obstacles. Microwaves are used in cooking due to their ability to efficiently heat water molecules, and in satellite communication because they can penetrate the Earth's atmosphere. Infrared radiation is valuable for thermal imaging, short-range communication, and remote controls. Visible light, the only part of the spectrum detectable by the human eye, is fundamental for sight, photography, and artificial illumination. Ultraviolet light has applications in security marking, sterilisation, and detecting forged documents. X-rays are crucial for medical imaging and security scanning due to their penetrating power. Finally, high-energy gamma rays are employed in medical treatments, such as radiotherapy, and for sterilising equipment and food by killing microorganisms.