Light

Spectrum and Vision

In the spectrum of light, there are seven colours: red orange yellow green blue indigo violet

As can be seen from the image, the colours nearer the red side have longer wavelengths. (All waves on the spectrum are electromagnetic.) Some examples of longer wavelengths include infrared waves (radiation) and radio waves. On the contrary, the colours nearer the blue/purple side have much shorter wavelengths, so short that they're measured in nanometres. Waves such as gamma rays and X-rays are good examples; both are used in medicine to see into the body and to destroy cancer cells.Vocabulary:Luminous: emits light (e.g: stars, light bulbs)Non-Luminous: does not emit light, but reflects it (e.g: planets, the Moon)

Directions:

There are three things that can happen to light when it hits an object: transmission: the light passes through. Like reflection, this occurs because the frequency of the light ray doesn't match the vibrating frequencies of the electrons in the object. When the light hits the object, the electrons only vibrate for a small period of time before the ray is re-emitted as a light wave once again. (In a transparent object, the vibrations are passed on throughout the atoms and consequently the light reappears on the other side of the object.) reflection: the light bounces. This usually happens when the object is opaque, as the electrons only vibrate shortly before re-emitting the energy as a light wave reflected off it. absorption (resonance): the light is sunk into the object. In this case, the light energy is converted into heat energy. This happens because the electrons in the object have a certain frequency/frequencies which they vibrate at, so when incident light of the same frequency hits the object, the electrons vibrate because they absorb the light's energy and convert it into vibration motions. Therefore the light ray itself is absorbed. Which frequencies of light that are absorbed depends on the object's electron's frequencies. Of course, light waves of various frequencies are usually incident on an object. In this case, depending on the atoms' nature and the light, for example, might absorb green light but reflect all other frequencies. Sometimes the three possibilities happen at the same time.

Types of Surfaces:

Transparent: transparent objects such as glass allow one or more frequencies of light to be transmitted, and typically, any other light frequencies that aren't transmitted are absorbed. The appearance and colour of the transparent object depends on the frequencies of the light rays incident upon it. Translucent: although light is transmitted through translucent objects, you cannot see very clearly through them. An example of this is frosted glass. Opaque: light cannot pass at all through opaque objects. They are completely solid.

Shadows:

Point Sources:Point sources are very small sources of light. They form sharp shadows, which means that light travels in straight lines. When the object is closer to the source, a bigger shadow is formed. Shadows can only be formed with translucent/opaque objects that are blocking the light.Broad Sources:Broad sources are larger sources of light and can often be more than one light. Shadows become more fuzzy and blurred, and there are partial shadows on either side of the object's complete shadow.

Colour:

White and pale objects reflect most of the light that is incident to them, because white light is made up of all the colours in the spectrum and therefore reflects all frequencies of light. However, black and dark objects don't reflect but instead absorb the light that is shone on them, because objects appear black since they don't reflect any colour.Usually, when an object absorbs a frequency of light (colour) that light is converted into another form of energy (for example, black objects absorb light and convert it into thermal heat energy.)

Primary and Secondary Colours:

With light, the three primary colours are red, blue and green. These colours can be mixed together to create the secondary colours: magenta, cyan and yellow. When mixing the colours together, it is an additive mixing if you are mixing the primary colours together to make the secondary colours. When you mix all three primary colours, you get white. Consequently, mixing the three secondary colours together to in turn create the primary colours is a subtractive mixing. (For example, inks and paint are subtractive mediums, so if you were to mix red, blue and green paint to attempt to make white it wouldn't work.)Wavelengths:Red light has the longest wavelength of all visible light (infrared rays have longer wavelengths than ultraviolet rays.) This means it is refracted the least. Therefore violet light has the shortest wavelength of all visible light, and is refracted more.Reflecting Colours:Which colour frequencies of light that are reflected completely depend on the "colour" of the object. For instance, if you shone white light on an apple, only the red light would be reflected (of the apple itself) because the apple is red. As prementioned, black objects absorb all colours and appear black, while white objects reflect all frequencies because white light is a mixture of all the colours.

Reflection:

normal: divides the angle between the angle of incidence and reflection.incident ray: the ray shone onto the mirrorreflection ray: the ray bounced offThe Law of Reflection:The Law of Reflection is i = r (angle of incidence = angle of reflection).

The dashed lines in the diagram are the image that is portrayed from the mirror. This is only a virtual, laterally inverted upright image. It can't be touched or projected, and you look the right way up when you look at it. It's also laterally inverted, and an example of this is that your left side looks like your right in the mirror.Periscopes:Periscopes have two mirrors to view objects that are out of our line of sight.

Refraction:

Refraction is the bending of light when it passes from one transparent medium to the other. This occurs because the light changes speed. For example, when it passes from a less dense medium to a denser medium, such as water, it slows down. As light passes from air to glass (less dense to denser) it bends towards the normal. On the other hand, when it passes from a denser to a less dense medium, it bends away from the normal.

Total Internal Reflection:

Critical Angle:The critical angle is the angle of incidence when the angle of reflection is equal to 90 degrees. Rays of light with an angle of incidence > than the critical angle are totally internally reflected.Some examples of these are optical fibres, which also use total internal reflection. The rays are reflected all the way down the fibre. When white light is passed through a triangular prism, it splits into the colours of the rainbow. This is known as dispersion.