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  critical angleangle of refractionspecial angletotal angle. For angles of incidence greater than the critical angle,  total internal angletotal internal refractiontotal internal reflectiontotal reflection occurs. Remember that this only happens when the incident medium is  more opaquedensermore solidharder 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  focal pointconvergenceprinciple focusprimary focus. Using a converging lens, a real image can be projected on a screen. With  a diverging lensan odd-shaped lensa thin lensa dispersing 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  reflectionrefractionpolarisationdiffraction 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  are always realare always virtualare always larger than the objectcan be either virtual or real, and convex lenses produce images which  are always larger than the objectare always realcan 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
•  ultravioletmicrowavesradio wavesinfrared – satellite communications, cooking food
• infrared – electrical heaters, cooking food, thermal cameras
• visible light –  medical imaging and treatmentscooking foodsatellite communicationsfibre-optic communications
•  ultravioletradio wavesinfraredmicrowaves – hospital sterilisation, suntanning
• X-rays and gamma rays –  fibre-optic communicationssatellite communicationsmedical imaging and treatmentscooking food

Gamma waves are produced by  oscillations in electrical currentshot objectschanges in nucleirotating atoms.

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 frequency at which the object vibratesthe temperature of the objectthe wavelengths of light reflected by 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  diffuseeffervescentspeculardifferential reflection. When a surface is rough, light is reflected in many different directions, known as  diffusespeculareffervescentdifferential reflection.
All objects emit radiation, with hotter objects emitting  higher intensity radiation at shorter wavelengthshigher intensity radiation at longer wavelengthslower intensity radiation at longer wavelengthslower intensity radiation at shorter wavelengths. A perfect black body absorbs and re-emits all incident radiation.