CHAPTER - 6

CHAPTER - 6

SPECTRUM

CHAPTER - 6DEVIATION 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 DEVIATIONThe angle of incidence at the first surface (i)The angle of Prism (A)The R.I. of the material of the prism ()TYPES OF LIGHTWhite Light:

Its 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 LIGHTA light, which is a mixture of several colours (waveband) is called polychromatic light.

DISPERSIONThe phenomenon of splitting of white light into its constituent colours is known as DISPERSION

SPECTRUMThe band of colours obtained on the screen, when a polychromatic light splits into component colours is called a Visible spectrum. 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.CAUSE OF DISPERSIONRECOMBINATION OF COLOURS

FREQUENCY AND WAVE LENGTH OF VISIBLE SPECTRUM

C = fC= speed of light. = wavelength of lightf = frequency of lightCOLOURIt is a sensation produced in the brain due to the excitation of the retina, by an E.M.Wave of some particular wavelength

ColorFrequency in 1014 HzWavelength violet6.737.54000 4460blue6.016.484640 5000green5.196.0150005780yellow5.085.1957805920orange4.845.0859206200red3.75 4.8462008000Electromagnetic Waves &the Electromagnetic Spectrum

Electromagnetic WavesTransverse 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 vibratesso does the other.

RESULT-An electromagnetic wave.

Electromagnetic Spectrumname for the range of electromagnetic waves when placed in order of increasing frequency

RADIO WAVESMICROWAVESINFRARED RAYSVISIBLE LIGHTULTRAVIOLET RAYSX-RAYSGAMMA RAYS

Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)RADIO WAVESHave the longest wavelengths and lowest frequencies 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.MICROWAVESHave 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 RAYSInfrared= below redShorter wavelength and higher frequency than microwaves.

PROPERTIESThey 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 0.8m to 40m.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.

Thermograma picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off.

Therefore people give off infrared rays.

Heat lamps give off infrared waves.

VISIBLE LIGHTShorter wavelength and higher frequency than infrared rays.Electromagnetic waves we can see.Longest wavelength= red lightShortest wavelength= violet (purple) light

ULTRAVIOLET RAYSShorter wavelength and higher frequency than visible lightCarry more energy than visible light

PROPERTIESThey 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 100AThey produce chemical effect in sliver. PROPERTIESThey 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)

Causes your skin to produce vitamin D (good for teeth and bones)

X- RAYSShorter wavelength and higher frequency than UV-raysCarry a great amount of energyCan penetrate most matter.

PROPERTIESX-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.

PROPERTIESThey travel in vacuum with the speed of light.They ionize the gas through which they pass.X-ray undergo reflection and refraction.

Bones and teeth absorb 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 RAYSShorter wavelength and higher frequency than X-raysCarry the greatest amount of energy and penetrate the most.

PropertiesHave 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.

PropertiesThey 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.

Exploding nuclear weapons emit gamma rays.

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 ScatteringWhen 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.Mie Scattering.

Fig. 15-8, p. 42051Figure 15.8: Because of the selective scattering of radiant energy by a thick section of atmosphere, the sun at sunrise and sunset appears either yellow, orange, or red. The more particles in the atmosphere, the more scattering of sunlight, and the redder the sun appears.