What is Light? PDF

What is Light? What is Light? - Form of energy that reaches us from the sun - Travels at very high speeds (3 x 10^8 m/s) - Travels in straight lines (ie. turning on a flashlight in a dark room) - White light is composed of a combination of many colours, ROYGBIV Electromagnetic Wave - Ha...

What is Light? What is Light? - Form of energy that reaches us from the sun - Travels at very high speeds (3 x 10^8 m/s) - Travels in straight lines (ie. turning on a flashlight in a dark room) - White light is composed of a combination of many colours, ROYGBIV Electromagnetic Wave - Has both electric and magnetic parts, does require a medium and travels at the speed of light - Medium - physical substance that allows energy to be transferred (ie. air, water) **Places without a medium are said to be in a vacuum (ie. no atmosphere, such as outer space) Electromagnetic Wave - Electricity and magnetism couple together (skip between the two to create the graph below) - Allows light to travel through space in the absence of a medium (ie. air) Electromagnetic Spectrum - Used to classify electromagnetic waves by energy - Entire range of wavelengths from the shortest wavelength (gamma ray) to the longest (radio wave) Electromagnetic Spectrum Examples - Radio waves - AM/FM radio, cellphones - Microwaves - microwave ovens - Infrared (IR) - remote controls, lasers, fast food restaurant heat lamps, physiotherapy - Visible light - human vision, rainbows, theatre/ concert lights - Ultraviolet (UV) - skin tans or burns, skin cancer, “black” lights - X-rays - medical imaging, security (airports), cancer treatment - Gamma rays - cancer treatment, nuclear reactions **All of electromagnetic spectrum is used for astronomy  Gamma Rays; wavelength 10-11 – 10-13 metres APPLICATIONS: -sterilizing medical equipment in hospitals -pasteurizing certain foods to prolong shelf life -treatment of cancer -radiography – patient ingests radioactive source X Ray; wavelength 10-9 – 10-11 metres APPLICATIONS: -radiography -treatment of cancer cells -airport security checks -studying atomic and molecular structure Ultra Violet light wavelength 10-7 – 10-8 metres APPLICATIONS: - criminology…. some stains (ie. blood) fluoresce under UV light - security ID marking - detection and destruction of bacteria - phototherapy treatment of skin complaints, e.g. psoriasis Visible Light - Electromagnetic waves that the human eye can detect - Visible spectrum - sequence of colours that make up white light (what ROYGBIV - Red, orange, yellow, we associated with green, blue, indigo, violet different colours) All of the colours we see come from white light, it’s our eyes that perceive different colours Visible Spectrum - Different wavelengths of light have different amounts of energy - Shorter wavelengths have more energy (ie. violet), longer wavelengths have less energy (ie. red)  Infrared wavelength about 1mm APPLICATIONS: -night-time surveillance -medical: laser surgery & thermal imaging -weather forecasting -remote controls -heat seeking missiles  Most “Light” is not visible Infrared radio/light waves have a very long wavelength; their wavelength is longer than visible light. Infra-red can be detected by special film and cameras. Animals like the pit-viper have infra-red vision so that they can find their warm prey in the dark.