Light Waves

Recap Light waves are medium-frequency transverse waves. Anything low-frequency or high-frequency is outside of what the human eye can detect. Light waves come from different sources: either the sun, fire or lightbulbs. Light waves are electromagnetic – meaning they can travel through a medium or a vacuum.

The electromagnetic spectrum

Light Waves In simplified diagrams, we depict light waves in a straight line. When these light waves strike a surface of something, one of three things can happen: They are reflected They are refracted They are absorbed Depends on the object that the light wave hits and its capacity to allow light to travel through it.

Reflection When light waves hit the surface of an object, they can be reflected. This occurs when light waves propagate through one medium and rebounds off of a different kind of medium. Ex: The sun’s light waves travel through the air and reflect of a mirror. All objects reflect light to some degree. This is how we can see, light reflecting off of objects brings light to our eyes.

Incident Ray: Ray that leaves the light source and contacts an object. Reflected Ray: Ray that rebounds. Normal: Perpendicular line coming from the reflected surface. Angle of incidence: Angle between the normal and the incident ray. Angle of reflection: Angle between the normal and the reflected ray.

… The reflection of light waves is governed by two laws: Angle of incidence and angle of reflection are always equal to one another. The incident rays and reflection rays are always on the same plane.

… There are two types of reflection: diffuse and specular reflection. Occurs when the surface of an object is uneven, (most objects). Therefore, the laws of reflection do not apply. Reflected light waves reflect in all directions.

… Specular: This occurs when light reflects off of a perfectly smooth surface. This follows the laws of reflection. When parallel light rays contact a smooth surface, their reflections are parallel. It will produce a true mirror-image.

Refraction Refraction is the deviation, (or bending), of a light ray as it passes from one transparent medium to another. The pencil appears bent because light has passed from air to water – both are transparent mediums. This happens because the speed of light changes as it passes from the air to the water, so the light ray deviates.

… Refraction changes our perception of objects as we look at them through a transparent medium. The most common application of refraction is in lenses.

Lenses Lenses are objects made of transparent materials that have at least one curved surface. Lenses are used in corrective eyewear, magnifying glasses, microscopes and camera lenses. There are two types of lenses: Converging – bring light rays together as they pass through. Also called convex. Diverging – Spread light rays out as they pass through. Also called concave.

Converging Lenses Converging lenses cause light rays to come together and reflect on one spot, called a focal point.

Diverging Lenses In a diverging lens, the light rays are refracted outwards, away from the focal point.

Real World Application This is how our eyes work, as we have lenses. In normal vision, the lens will adjust its shape according to objects that are nearer or further. This causes the focal point to always be on the retina. Images will form correctly.

… People who are nearsighted, (can only see clearly up close), the converging lens of the eye does not adjust correctly. Therefore the focal point ends up being in front of the retina. Images further away are fuzzy and unclear. Diverging lenses correct this. Called myopia.

… People who are farsighted, (can only see further away), have the opposite problem. The near object image is formed behind the retina. Therefore, objects up close are fuzzy and unclear. Corrected with a converging lens. Called hyperopia

Normal View Myopia Hyperopia Near Sighted Far Sighted