## What is light?

Light is a term that refers to a type of electromagnetic radiation that we can see with our own eyes. All types of electromagnetic radiation (including light) can be described as tiny particles, called photons, that travel in transverse waves. Transverse waves are waves where a disturbance or transfer of energy moves perpendicular to the direction a wave is traveling in. For example, the up and down motions of water ripples or wiggling a rope can be described as transverse waves.

Here are some characteristics of a transverse wave:

• Crest: the highest part of the wave

• Trough: the lowest part of the wave

• Amplitude: how high the crest is/how low the trough is. A larger amplitude yields a stronger wave

• Wavelength: the distance between two identical, repeating points on a wave (for example, the distance between two crests on a wave)

1. Waves with shorter wavelengths have higher energy because they vibrate faster than long wavelengths

2. Light and other types of electromagnetic radiation are typically measured in nanometers (nm)

## What is the visible spectrum?

The visible spectrum is simply just the types of light we can see! Remember: light is already defined as electromagnetic radiation we can see, so the visible spectrum is just the range of wavelengths visible to our eyes. The different “types” are often referred to as colors, the main ones being red, orange, yellow, green, blue, and violet (purple). You can remember these colors with the acronym ROY G BV.

The visible spectrum covers a range of wavelengths from 380 nm (violet) to 750 nm (red). The colors in ROY G BV are arranged from longest to shortest wavelength. Since the shorter a wavelength is, the more energy it has, we can say that violet light has more energy than red light.

Virtually everything around you has color to it because different objects reflect light back to your eyes. For example, an apple appears red to us because it absorbs most of the other light/colors and reflects red light to our eyes. Objects that appear white reflect ALL colors back to our eyes. Black objects have an absence of color due to their inability to reflect light.

## Opacity, Translucency, and Transparency

Some objects are see-through, while others are not. This is due to the objects’ ability to allow light to pass through them.

1) An object is described as opaque when it is incapable of letting light pass through it, making it impossible to see through. An example would be a black sheet of paper.

2) An object is described as translucent when it allows some light to pass through it. Because not all light is able to travel through the object, images on the other side of the object may appear fuzzy or not clearly visible. The translucent object tends to distort images because it doesn’t allow all light to pass through. An example would be a foggy window or dirty water.

3) An object is described as transparent when it is capable of allowing nearly ALL light to pass through it. Since the path of the light is virtually undisturbed you can see clear, distinct images on the other side of the object. For example, glass and plastic wrap are transparent.

## Reflection and Refraction

Light can reflect off of certain surfaces, causing them to bounce off of them into a different direction. This is because some objects do not absorb light or allow it to pass through them very well, forcing the light wave to reflect into a different direction. A mirror is a perfect example of a reflective surface; we can see ourselves in mirrors because our images are reflected off of mirrors and back to our eyes.

Refraction is when light passes through an object that slows it down or causes it to change direction slightly. It is different from reflection because the object still lets light pass through and travel in the same general direction. However, refracted images often become distorted because the light’s path is slightly altered. Have you ever noticed that a straw looks bent or broken inside a glass of water, but normal before you put it in the glass? That’s because the water has a different refractive index than air, so the light that travels through the water, the glass, and then the air gets distorted in the process.

Refraction can cause images to flip over, change size, and bend/distort from what the real object looks like normally.

### Refraction in Prisms

You can separate white light into its individual colors by using a prism. A prism is a transparent, wedge-shaped object. Because different colors have different wavelengths, their speeds--and thus the amount that they refract inside the prism--allows them to bend at different angles, eventually exiting the prism as an ordered stack of colors: a rainbow.