ELECTROMAGNETIC WAVES MAXWELL’S EQUATIONS

ELECTROMAGNETIC WAVES

INTRODUCTION JAMES CLARK MAXWELL OF SCOTLAND GAVE A SET OF FORMULAE FOR ELECTRIC CHARGE, CURRENT AND THEIR ELECTRIC FIELD AS WELL AS MAGNETIC FIELD. THESE FORMULAE EMPHASIZE ON THE INTER RELATION BETWEEN ELECTRICITY AND MAGNETISM. MAXWELL HAS GIVEN FOUR EQUATIONS CONNECTING MAGNETIC FIELD AND ELECTRIC FIELD.

MAXWELL’S EQUATIONS AMPERE-MAXWELL CIRCUITAL LAW: 𝐵.𝑑𝑙 =𝜇 𝑜 𝐼𝑐+𝜖𝑜 µ 𝑜 𝑑∅ 𝐸 𝑑𝑡 GAUSS LAW OF ELECTROSTATICS: 𝐸.𝑑𝑆=𝑄/∈𝑜 GAUSS LAW FOR MAGNETISM: 𝐵.𝑑𝑆=0 FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION: 𝐸.𝑑𝑙=− 𝑑∅ 𝐵 𝑑𝑡

EM WAVES - SOURCE BASIC SOURCES OF ELECTROMAGNETIC WAVES A CHARGE OSCILLATING HARMONICALLY IS A SOURCE OF ELECTROMAGNETIC WAVE OF SAME FREQUENCY. H.R. HERTZ EXPERIMENT CONFIRMED THE FACT THAT A VIBRATING ELECTRIC CHARGE RADIATES ELECTROMAGNETIC WAVES.

SOURCE OF EM WAVES LATER ON J.C.BOSE HAS SUCCESSFULLY PRODUCED ELECTROMAGNETIC WAVES IN HIS LABORATORY IN CALCULLTA AFTER 8 YEARS. IN 1895, MARCONI MADE AN IMPORTANT DISCOVERY WHICH LED TO THE COMMERCIAL USE OF EM WAVES IN THE FILED OF COMMUNICATION.

CHARACTERISTIC PROPERTIES OF ELECTROMAGNETIC WAVES EM WAVES DO NOT REQUIRE ANY MEDIUM FOR PROPAGATION. SPEED OF EM WAVES IN FREE SPACE OR VACUUM IS EQUAL TO 3 LAKH KM PER SECOND. C = 1 𝜇𝑜𝜖𝑜 SPEED OF EM WAVES IN A MEDIUM IS GIVEN BY v = 1 𝜇𝜖

PROPERTIES OF EM WAVES EM WAVES ARE SELF SUSTAINING ELECTRIC AND MAGNETIC FIELD OSCILLATIONS IN SPACE. EM WAVES ARE TRANSVERSE IN NATURE i.e. THE ELECTRIC FIELD AND MAGNETIC FIELD ARE PERPENDICULAR TO EACH OTHER AS WELL AS PERPENDICULAR TO THE DIRECTION OF PROPAGATION OF THEWAVE.

PROPERTIES OF EM WAVES THE AMPLITUDES OF ELECTRIC FIELD AND MAGNETIC FIELD ARE RELATED TO EACH OTHER BY A RELATION c = 𝐸𝑜 𝐵𝑜 EM WAVES CAN BE REFLECTED, REFRACTED AND DIFFRACTED. EM WAVES SHOW THE PHENOMENON OF INTERFERENCE.

PROPERTIES OF EM WAVES EM WAVES CAN BE POLARISED. EM WAVES ARE NOT DEFLECTED Y MAGNETIC AND ELECTRIC FIELDS. INTENSITY OF AN EM WAVE DEPENDS UPON THE AMPLITUDE OF ELECTRIC FIELD AND MAGNETIC FIELD. EM WAVES TRANSPORT ENERGY.

ELECTROMAGNETIC SPECTRUM

REGIONS OF EM SPECTRUM AN EM SPECTRUM CONSISTS OF THE FOLLOWING WAVES: 1. RADIO WAVES 2. MICRO WAVES 3. INFRARED WAVES 4. VISIBLE LIGHT 5. ULTRA-VIOLET WAVES 6. X – RAYS 7. GAMMA RAYS

RADIO WAVES WAVELENGTH RANGE: 0.3m TO 600nm FREQUENCY RANGE: 500kHz TO 1000MHz SOURCE: ACCELERATED CHARGED PARTICLES IN A CONDUCTING WIRE OR CHANGING ELECTRIC CURRENT IN LC CIRCUIT. USES: MAINLY USED IN RADIO AND TELEVISION COMMUNICATION.

MICRO WAVES WAVELENGTH RANGE: 0.1m TO 1 mm FREQUENCY RANGE: 10 9 Hz TO 10 12 Hz SOURCE: Oscillating electrons in a cavity commonly used oscillators to produce micro waves are Klystron, Magnetron Gunn diodes. USES: USED IN RADAR SYSTEMS FOR AIRCRAFT NAVIGATION. USED FOR ATOMIC AND MOLECULAR RESEARCH.

MICRO WAVES – USES USED IN MICRO WAVE OVENS FOR COOKING AND WARMING OF FOOD. USED FOR COMMUNICATION BY CELLULAR PHONES. USED IN WEATHER RADAR.

INFRA-RED(IR) WAVES WAVELENGTH RANGE: 1mm TO 700 nm FREQUENCY RANGE:10 11 Hz TO 10 14 Hz SOURCE: HOT BODIES(VIBRATIONS OF ATOMS/MOLECULES) USES: These waves can pass through the haze, fog and mist, so they are used in night vision devices during warfare. Infra red detectors are used by earth satellites. Used to function the green houses because green house gas and water vapours absorb the infrared waves readily.

INFRA-RED WAVES USED IN REVEALING THE SECRET WRITINGS ON THE ANCIENT WALLS INFRARED LAMPS ARE USED TO TREAT MUSCULAR STRAINS. INFRARED REMOTES ARE USED TO OPERATE ELECTRONIC DEVICES LIKE TV, VCD etc. THE INFRA-RED WAVES KEEP THE EARTH WARM.

VISIBLE LIGHT WAVELENGTH RANGE: 400 nm TO 780 nm FREQUENCY RANGE: 4 X 10 14 Hz TO 7 X 10 14 Hz SOURCE: JUMPING OF ELECTRON FROM HIGHER ORBIT TO LOWER ORBIT OF AN ATOM USES:IT STIMULATES THE SENSE OF SIGHT IN HUMAN BEINGS, SO THE BEAUTIFUL WORLD AROUND US IS SEEN THE PRESENCE OF VISIBLE LIGHT.

USES OF VISIBLE LIGHT IS USEFUL IN PHOTOGRAPHY IS USEFUL IN OPTICAL MICROSCOPY IS USEFUL IN ASTRONOMY IT IS A GREAT SOURCE OF ENERGY FOR HUMAN LIFE.

ULTRA-VIOLET(UV) WAVES WAVELENGTH RANGE: 400 nm TO 0.6 nm FREQUENCY RANGE:7.5 X 10 14 Hz TO 5 X 10 15 Hz SOURCE: THE SUN, WELDING ARC, HIGH VOLTAGE GAS DISCHARGE TUBE. USES:THEY ARE USED TO PRESERVE FOOD STUFF AND MAKE DRINKING WATER FREE FROM BACTERIA. USED FOR STERILIZING THE SURGICAL INSTRUMENTS.

UV WAVES USED IN DETECTING THE INVISIBLE WRITINGS, FORGED DOCUMENTS AND FINGER PRINTS. TO STUDY THE STRUCTURE OF MOLECULES. ARE USED IN LASIK EYE SURGERY AS UV WAVES CAN BE FOCUSSED INTO A NARROW BEAMS.

X-RAYS WAVELENGTH RANGE:10 nm to 10 -4 nm FREQUENCY RANGE:10 18 Hz TO 10 20 Hz SOURCE:FAST MOVING ELECTRONS STRIKING A TARGET OF HIGH AOMIC NUMBER. USES: USED IN MEDICAL DIAGNOSIS IN RADIO THERAPY TO CURE SKIN DISEASES, CANCERS AND TUMORS. IN ENGINEERING FOR LOCATING FAULTS OR CRACKS IN METALLIC MATERIALS.

GAMMA RAYS USES:USED FOR TREATMENT OF CANCER. WAVELENGTH RANGE:10 -10 m to 10 -14 m FREQUENCY RANGE:10 18 Hz TO 10 22 Hz SOURCE:RADIOACTIVE DECAY OF NUCLEI AND NUCLEAR REACTIONS. USES:USED FOR TREATMENT OF CANCER. TO EXAMINE THE THICK MATERIALS FOR STRUCTURAL FLAWS. FOR FOOD PRESERVATION.

EM WAVES THE END.