CHAPTER - 6 SPECTRUM
DEVIATION The angle between the incident ray and the emergent ray is called the angle of deviation. It is represented by d
FACTORS AFFECTING ANGLE OF DEVIATION • The angle of incidence at the first surface (i) • The angle of Prism (A) • The R.I. of the material of the prism (μ)
TYPES OF LIGHT White Light: It’s a polychromatic light and has all the seven wavebands present in it. Monochromatic Light: A light which consists of one colour (one wavelength) only is called monochromatic light
POLYCHROMATIC LIGHT A light, which is a mixture of several colours (waveband) is called polychromatic light.
DISPERSION • The phenomenon of splitting of white light into its constituent colours is known as DISPERSION
SPECTRUM The band of colours obtained on the screen, when a polychromatic light splits into component colours is called a Visible spectrum.
CAUSE OF DISPERSION When white light is incident on the first surface of a prism and enters it, light of different colours is refracted (or deviated) through different angles.
FREQUENCY AND WAVE LENGTH OF VISIBLE SPECTRUM C = λf C= speed of light. λ = wavelength of light f = frequency of light
COLOUR • It is a sensation produced in the brain due to the excitation of the retina, by an E.M.Wave of some particular wavelength
Electromagnetic Waves • Transverse waves without a medium! • (They can travel through empty space)
They travel as vibrations in electrical and magnetic fields. • Have some magnetic and some electrical properties to them.
When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other. • RESULT-An electromagnetic wave.
Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency GAMMA RAYS ULTRAVIOLET RAYS RADIO WAVES INFRARED RAYS X-RAYS MICROWAVES VISIBLE LIGHT
Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)
RADIO WAVES • Have the longest wavelengths and lowestfrequencies of all the electromagnetic waves.
Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from several satellites to the receiver, determining the distance to each satellite.
A radio picks up radio waves through an antenna and converts it to sound waves. • Each radio station in an area broadcasts at a different frequency. • # on radio dial tells frequency.
MRI • (MAGNETIC RESONACE IMAGING) • Uses Short wave radio waves with a magnet to create an image.
MICROWAVES • Have the shortest wavelengths and the highest frequency of the radio waves.
Used in microwave ovens. • Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.
RADAR (Radio Detection and Ranging) • Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
INFRARED RAYS • Infrared= below red • Shorter wavelength and higher frequency than microwaves.
PROPERTIES • They are not affected by electric or magnetic field. • They travel with the velocity of light. • They obey the laws of reflection and refraction. • They are least scattered by fog, mist, etc.
Their wavelength is between 0.8μm to 40μm. • They do not affect ordinary photographic film. • They can be detected by a thermopile or a thermometer.
You can feel the longest ones as warmth on your skinWarm objects give off more heat energy than cool objects.
Therefore people give off infrared rays. Heat lamps give off infrared waves. Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off.
VISIBLE LIGHT • Shorter wavelength and higher frequency than infrared rays. • Electromagnetic waves we can see. • Longest wavelength= red light • Shortest wavelength= violet (purple) light
ULTRAVIOLET RAYS • Shorter wavelength and higher frequency than visible light • Carry more energy than visible light
PROPERTIES • They are e.m.waves and are not effected by electric or magnetic field. • They travels with the velocity light. • The range of these radiations is between 4000A to 100A • They produce chemical effect in sliver.
PROPERTIES • They obeys the laws of reflection and refraction. • They are absorbed by the atmosphere and convert oxygen to ozone. • They produced fluorescence in substance like zinc sulphide, barium sulphide, etc.
Too much can cause skin cancer. • Use sun block to protect against (UV rays)
X- RAYS • Shorter wavelength and higher frequency than UV-rays • Carry a great amount of energy • Can penetrate most matter.
PROPERTIES • X-Ray are e.m.wave of very short wavelength ranging from 10-12m to 10-10m. • They are not effected by electric and magnetic field. • They effect the photographic plate intensely.
PROPERTIES • They travel in vacuum with the speed of light. • They ionize the gas through which they pass. • X-ray undergo reflection and refraction.
Bones and teethabsorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
Too much exposure can cause cancer • (lead vest at dentist protects organs from unnecessary exposure)
Used by engineers to check for tiny cracks in structures. • The rays pass through the cracks and the cracks appear dark on film.
GAMMA RAYS • Shorter wavelength and higher frequency than X-rays • Carry the greatest amount of energy and penetrate the most.
Properties • Have velocity equal to that of light. • Have high penetrating power. They can penetrate through several centimeters thick iron and lead blocks. • They have got small ionizing power. • They can effect a photographic plate.
Properties • They can produce heating effect in the surface exposed to them. • They are not deflected by electric and magnetic fields. • They knock out electrons from the surface on which they fall.
Used in radiation treatment to kill cancer cells. • Can be very harmful if not used correctly.
Rayleigh Scattering When a photon penetrates into a medium composed of particles whose sizes are much smaller than the wavelength of the incident photon, the scattering process is elastic and is called Rayleigh scattering. In this scattering process, the energy (and therefore the wavelength) of the incident photon is conserved and only its direction is changed. In this case, the scattering intensity is proportional to the fourth power of the reciprocal wavelength of the incident photon. The scattering of electromagnetic radiation by particles with dimensions much smaller than the wavelength of the radiation, resulting in angular separation of colors and responsible for the reddish color of sunset and the blue of the sky.
Light Scattering When light encounters matter, matter not only re-emits light in the forward direction (leading to absorption and refractive index), but it also re-emits light in all other directions.This is called scattering. Light scattering is everywhere. All molecules scatter light. Surfaces scatter light. Scattering causes milk and clouds to be white and water to be blue. It is the basis of nearly all optical phenomena. Scattering can be coherent or incoherent.