# Light

If you've been to the beach, you've seen waves crashing onto the sand. But did you know that light is also a type of wave? Even though it's different from water waves, it follows similar patterns. Just like ocean waves, light waves can reflect, refract, and diffract. It's pretty cool!

## The definition of light

Before we can discuss how light behaves, we must be able to identify what light is. There are many descriptions that can be used to classify waves but to avoid confusion, we will consider light as purely a wave. We can then define it as below.Light is defined as an electromagnetic wave with a wavelength in the visible part of the electromagnetic spectrum (380 to 700 nanometres). That is, light is any electromagnetic wave that we can see with our eyes.

## The nature of light

We've established that light behaves like a wave, which means it has a wavelength and travels in a straight line. The wavelength is the distance between two identical points on the wave, like two or two valleys. Different wavelengths of light create different colors that we see. For example, the color red has a wavelength of about 650 nanometers, which why a red rose on a sunny day reflects red light that we can see. is a type of transverse wave, meaning that electric and magnetic fields oscillate up and down as the wave travels. When all the colors of visible light are combined, we get white light, like the light from the sun. You can see this when white light passes through a glass prism and separates into all the colors of the rainbow.

White light, once dispersed, gives us all the colours in the visible electromagnetic spectrum, which is what you would see in a rainbow. Red light has a wavelength of about 700 nanometres (700 x 109 metres), while violet light at the opposite end of the electromagnetic spectrum has a wavelength of about 380 nanometres.

## The speed of light

All waves, including light waves, are essentially oscillations carrying energy as they move. This means that light also has a speed and that it's the fastest speed in the universe. The speed of light in free space is a constant at 300 million meters per second or 3.00 x 108 m/s. It's essential to note that light's speed is constant in a vacuum, regardless of the color or wavelength of the light. We can use the wave equation to understand how the frequency and wavelength of light are related to its speed. The frequency of a wave is the number of complete oscillations passing a fixed point every second and is measured in Hz. The wavelength is the distance between two identical points on the wave. By using the wave equation, we can calculate the wavelength of light, given its frequency and speed. For instance, the wavelength of red light from a 4.6 x 1014 Hz laser is 6.52 x 10-7 meters.

## The properties of light

There are many properties of light waves, but we will discuss two in detail: reflection and refraction. These are two of the more important properties of light, which can be used to make observations of distant objects in the universe.

### Reflection

As we discussed earlier, the color of a rose is due to visible light reflecting off its surface. This reflection is a property of wave motion exhibited by light. Reflection takes place when light moves through a medium and hits a boundary between two different media. The light either bounces back off the boundary or changes direction and moves on in the original medium. The diagram below illustrates this phenomenon.

In a plane mirror, the angle of incidence is equal to the angle of reflection. This means that the incoming electromagnetic ray and the reflected ray form equal angles with respect to the plane mirror. To understand this, imagine standing in the path of the reflected ray and replacing the plane mirror with a calm blue lake. The lake reflects visible light rays from the sky, including clouds, and sends the reflected rays into your eyes. This is why you can view the sky and clouds above while looking down at the lake. The same principle applies to plane mirrors, where incoming light reflects off the mirror and enters our eyes, allowing us to see a reflection of ourselves or the surrounding environment.

### Refraction

Another property of wave motion displayed by visible light is refraction. Refraction occurs when light rays move from one medium to another and change direction and speed in the process. The red arrow in the figure below illustrates this phenomenon. The extent to which a light ray is refracted when moving between different media depends on the types media and the wavelength (color) of the incident light. Refraction is responsible for the phenomenon of apparent depth, which is why objects in deep pools or lakes appear closer to the surface than they actually are. This phenomenon has tricked many fishermen in the past. To illustrate this, consider a pencil placed in a beaker of water. The bottom end of the pencil lies at point X but appears to be located at Y to someone observing from above. We say that the apparent depth of the bottom end of the pencil is the distance from Y to the surface, as shown in the illustration below.

### Other properties of light

Reflection and refraction are two important properties of light waves, but they are not the only ones. Other properties of light include interference, diffraction, polarisation, scattering, and dispersion. A deeper study of each of these properties can provide insights into the phenomena we experience every day but cannot explain. Here are some key takeaways about light: it is a wave that falls in the visible part of the electromagnetic spectrum and travels in straight lines. The wavelength of a visible light wave determines its color, with violet light having a wavelength of 380 nanometers and red light having a wavelength of 700 nanometers. The speed of light in free space is 300 million meters per second, and the wave equation is given by c = f x λ, where λ is the wavelength of light and f is the frequency. Reflection occurs when a ray of light strikes the boundary between two media and stays in its original medium, while refraction occurs when a ray of light strikes the boundary between two media and moves from the first medium into the second, changing direction and speed in the process. The apparent depth of objects submerged in water can be explained by refraction.

## Light

What are the characteristics of light?

Light behaves both as a wave and particle. Light has a speed of 300 million metres per second.

What are the types of light?

The types of light are the different colours that correspond to different wavelengths in the visible region of the electromagnetic spectrum.

What is the nature of light?

Light can act as both a particle and a wave.

How does light work in physics?

Light is an electromagnetic wave that carries energy in the visible spectrum. Humans can perceive light waves with their eyes.

What are the properties of light?

The properties of light are refraction, reflection, diffraction, interference, dispersion, polarisation, and scattering.