Light and the electromagnetic spectrum GapFill

Ray diagrams are used to illustrate the passage of waves. When a ray is passing from a more to a less dense medium and the angle of incidence is increased, the angle of refraction also increases until it approaches 90°. At this point the ray is refracted along the boundary. The angle of incidence at this point is known as the  special anglecritical angleangle of refractiontotal angle. For angles of incidence greater than the critical angle,  total internal angletotal internal reflectiontotal reflectiontotal internal refraction occurs. Remember that this only happens when the incident medium is  denserhardermore opaquemore solid than the surrounding medium. Refraction is used in lenses to focus light and create an image. In a converging lens, parallel rays of light are brought to a focus; this is called the  primary focusprinciple focusconvergencefocal point. Using a converging lens, a real image can be projected on a screen. With  a diverging lensa thin lensa dispersing lensan odd-shaped lens, parallel light is spread out so as to appear to come from the principle focus. This type of lens creates a virtual image which cannot be projected onto a screen. The power of a lens is related to its  primary focusconverging powerfocal pointfocal length and its shape

When light moves from one material into another, it can change direction due to the change in speed of the light; this is called  polarisationdiffractionreflectionrefraction and is used in lenses.
Lenses can change the apparent size of an object; the change in size is known as magnification, which is given by the equation magnification =  image size ÷ object sizeobject size ÷ image sizeimage size + object sizeimage size × object size.
Lenses can either be either (the outer edge is thicker than the middle) or convex (the middle is thicker than the edge). Concave lenses produce images which  can be either virtual or realare always virtualare always larger than the objectare always real, and convex lenses produce images which  are always realare always larger than the objectcan be either virtual or realare always virtual.

Electromagnetic waves are transverse waves in electric and magnetic fields. Electromagnetic waves can have a variety of wavelengths and frequencies, forming a continuous spectrum.
The regions of the electromagnetic spectrum with some applications, from longest to shortest wavelength, are:

• radio waves – television and radio broadcasts
•  microwavesultravioletradio wavesinfrared – satellite communications, cooking food
• infrared – electrical heaters, cooking food, thermal cameras
• visible light –  satellite communicationsfibre-optic communicationscooking foodmedical imaging and treatments
•  ultravioletmicrowavesradio wavesinfrared – hospital sterilisation, suntanning
• X-rays and gamma rays –  cooking foodfibre-optic communicationssatellite communicationsmedical imaging and treatments

Radio waves are produced by  rotating atomshot objectschanges in nucleioscillations in electrical currents.
Gamma waves are produced by  oscillations in electrical currentsrotating atomschanges in nucleihot objects.

Visible light can have many different colours, called the colour spectrum, which includes red, orange, yellow, green, blue, indigo and violet. Which colour an opaque object appears to be is related to  the wavelengths of light reflected by the objectthe frequency at which the object vibratesthe temperature of the objectthe intensity of light reflected from the object.
Visible light can be reflected, as seen in mirrors. When a surface is smooth, like a mirror, all the light is reflected in a single direction, known as  effervescentspeculardiffusedifferential reflection. When a surface is rough, light is reflected in many different directions, known as  effervescentdifferentialdiffusespecular reflection.
All objects emit radiation, with hotter objects emitting  lower intensity radiation at longer wavelengthshigher intensity radiation at shorter wavelengthshigher intensity radiation at longer wavelengthslower intensity radiation at shorter wavelengths. A perfect black body absorbs and re-emits all incident radiation.