The human eye is a fascinating thing. Windows to the brain, each image you see, instantly clicking into you're memory, understanding what you see through you're eyes, is what is around you. But have you ever wondered how it all works? Light. Light is the answer to that question. The simple word is a marvelous thing that allows you to absorb your surroundings. Without light, all there is, is darkness. Complete and utter darkness. You wouldn't be able to see a single movement or anything, in fact without it. So how does it all work? How does light allow us to see things?" - QueenCleoP
How does light work?
Light is at once both obvious and mysterious. We are bathed in yellow warmth every day and stave off the darkness with incandescent and fluorescent bulbs. Light travels in straight lines as waves. These are transverse waves like ripples in a tank of water. Unlike sound waves, light waves can travel through a vacuum (empty space). They do not need a substance to travel through, but they can travel through transparent and translucent substances. For example, windows or glass doors.
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Refraction
Sound waves and light waves change speed when they pass across the boundary between the two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction. There is one special case. Refraction doesn't happen if they cross the boundary at an angle of 90°- In that case, they carry straight on. Sound and light behave just like water waves in a ripple tank. The bending follows a regular pattern.
Reflection |
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Sound waves and light waves reflect from surfaces. They behave like water waves in a ripple tank. The angle of incidence equals the angle of reflection. When light reaches a mirror, it reflects off the surface of the mirror. The law of reflection states that the angle of incidence equals the angle of reflection, i = r. It works for any angle, for example, the angle of reflection is 30° if the angle of incidence is 30° and the angle of reflection is 90° if the angle of incidence is 90°.
When you think of reflection, think about mirrors. They reflect all of the light. That is the reason you can see yourself. Even the ocean reflects light, just not all of it. If you are above the ocean, you can't see the reflection that well, but when you are at an angle, look closely; you can see a reflection of the sky. So the ocean only has partial reflectivity. Reflection can happen in two quite different ways. If you have a smooth, highly polished surface and you shine a narrow beam of light at it, you get a narrow beam of light reflected back off it. This is called specular reflection and it's what happens if you shine a flashlight or laser into a mirror: you get a well-defined beam of light bouncing back towards you. Most objects aren't smooth and highly polished: they're quite rough. So, when you shine light on them, it's scattered all over the place. This is called diffuse reflection and it's how we see most objects around us as they scatter the light falling on them. If you can see your face in something, it's specular reflection; if you can't see your face, it's diffuse reflection. Polish up a teaspoon and you can see your face quite clearly. But if the spoon is dirty, all the bits of dirt and dust are scattering light in all directions and your face disappears. |
Spectrum of Light
White light is a mixture of many different colours, each with a different frequency. White light can be split up into a spectrum of these colours using a prism, a triangular block of glass. Light is refracted when it enters the prism, and each colour is refracted by a different amount. This means that the light leaving the prism is spread out into its different colours, a process called dispersion.
Here are the seven colours of the spectrum listed in order of their frequency, from the lowest frequency (fewest waves per second) to the highest frequency (most waves per second):
Red
Orange
Yellow
Green
Blue
Indigo
Violet
This mnemonic is one way to remember the order: ‘Richard Of York Gave Battle In Vain’.
Here are the seven colours of the spectrum listed in order of their frequency, from the lowest frequency (fewest waves per second) to the highest frequency (most waves per second):
Red
Orange
Yellow
Green
Blue
Indigo
Violet
This mnemonic is one way to remember the order: ‘Richard Of York Gave Battle In Vain’.