Understanding the Physics of Light and Optics

The Importance of Light

Light is an essential form of energy for life on Earth. It is electromagnetic radiation within a specific portion of the electromagnetic spectrum. The term usually refers to visible light, which is detectable by the human eye and is responsible for our sense of sight.

How Light Travels

Light travels as transverse waves, similar to ripples in a tank of water. The direction of vibration in these waves is at 90° to the direction of travel. Because light travels in straight lines, you should always use a ruler when representing a ray of light in a drawing.

Unlike sound waves, light can travel through a vacuum (empty space). It does not require a medium to propagate, though it can pass through:

• Transparent substances: Matter you can see through clearly.
• Translucent substances: Matter that allows light to pass through but is not completely clear.

Reflecting Light

We see objects because they reflect light, which is then captured by our eyes.

Smooth Surfaces

When a light ray strikes a smooth surface, the angle of reflection is equal to the angle of incidence. When this reflected light reaches your eyes, you are able to see an image.

Rough Surfaces

Light rays that strike a rough surface do not have the same angle of incidence and reflection. Consequently, you cannot see your image in a rough surface. This occurs because light is scattered in all directions, a process known as diffuse scattering. This explains why you see a clear reflection in a mirror but not on a dull, rough wall.

Refraction

Refraction is the bending of light caused by changes in speed when passing through different media. The angle that the ray makes with the normal is called the angle of refraction.

• If light slows down, it bends toward the normal.
• A light ray can appear to come from a different direction than the actual object, such as a stone appearing displaced in water.

The Prism

If sunlight strikes a prism at a specific angle and is projected onto a white screen, it creates a range of colors called a spectrum. Sunlight contains different colors because they have different wavelengths and travel at different speeds.