# Electromagnetic Wave

16. Feb 2021                                               1 von 47

### Electromagnetic Wave

• 1. Class -12th PRIYANKA JAKHAR PHYSICS LECTURER GGIC VIJAY NAGAR GHAZIABAD Electromagnetic waves
• 2. (Waves) Mechanical waves Electromagnetic waves requirement of medium No requirement of medium Transverse wave Longitudinal wave Consist no. of patterns of different frequency A wave is a physical phenomenon characterized by its frequency, wavelength, and amplitude. In general, waves transfer energy from one location to another, in which case they have a velocity. A wave is a disturbance that moves energy from one place to another. (Waves)
• 3. Mechanical waves The waves which require a material medium for their propagation are known as mechanical waves Examples •Water waves •sound waves •Spring waves •waves of the tuning fork Electromagnetic Waves The waves which require no material medium for their propagation are called electromagnetic waves. These waves propagate out in space due to the oscillation of electric and magnetic fields. examples •Light waves •Heat waves •radio waves •X-Ray waves
• 4. medium vibrates at right angles to the direction of its propagation. the displacement of the medium is in the same direction sound waves. ultrasound waves. seismic P-waves ripples on the surface of water. Vibrations in a guitar string. एक्स-किरण radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.
• 5. Transverse Waves --A wave in which particles of the medium move perpendicularly to the direction of the wave is called a transverse wave. Waves that are produced in water are transverse waves. Observes transverse waves produced by the up and down movement of a rope. The highest point of a transverse wave is called crest. The lowest point between two crests is called Trough. Longitudinal waves ---A wave in which particles of a medium move back and forth, parallel to the direction of the wave is called a longitudinal wave.If we pull and push one end of the slinky spring continuously, we can produce a longitudinal wave. The part of a longitudinal wave, where particles of the medium are compressed together, are called compressions. The part of a longitudinal wave, where particles of the medium are spread out, are called rarefactions. As the wave moves, compressions and rarefactions are produced due to the back and forth motion of particles of the medium. Sound from a vibrating body produces longitudinal
• 7. (Electromagnetic Wave) (Electricity) + (magnetism) + (waves) v=0 Stationary charge v=uniform Moving charge v=increasing Acceleratory charge Electric field Magnetic field & Electric field (EMW)
• 8. According to Faraday's law:-- (1830) Time varying magnetic field creates changing electric field around it. According to Oersted:- (1820) when a steady electric current passes through a wire it creates a magnetic field around it.
• 9. According to Maxwell :--Analysed that converse of Faraday’s law is also true. Time varying electric field creates changing magnetic field around it. B E B E B E B Theory of EMW was mainly developed by Maxwell around 1864.
• 10. Maxwell's equations:-Maxwell formulated the basis laws of electricity and magnetism in the form of four fundamental equations. Gauss's law in electricity Gauss's law in magnetism Faraday's law Ampere -Maxwell law Ampere's law Maxwell's law These four equations represent the relationship between electric field, magnetic field, electric charge and magnetic charge In the absence of any dielectric or magnetic material.
• 11. •Electric charge q produces an electric field E •The electric field flux passing through any closed surface is proportional to the total charge contained within that surface Gauss's law in magnetism •The total magnetic flux passing through any closed surface is 0. •The assumption that there are no magnetic monopoles. •There are no magnetic flow sources, and the magnetic flux lines always close upon themselves. •Also called the law of conservation of magnetic flux Faraday's law •Changing magnetic flux through a surface induces an electromotive force (EMF) in any boundary path of that surface. •A changing magnetic field induces a circulating electric field. •The voltage accumulated around a closed circuit is proportional to the time rate of change of the magnetic flux it encloses. •An electric current I or a changing electric flux through a surface produces a circulating magnetic field around any path that bounds that surface. •Electric currents and changes in electric fields are proportional to the magnetic fields circulating about the areas where they accumulate. Gauss's law in electricity Ampere -Maxwell law
• 12. Displacement current:- Displacement current is the current that is included to explain the magnetic field inside the capacitor due to mounting up of charges on its plates. Conduction current:- Conduction current is the electric current that flows through a conductor because of an applied potential difference.
• 14. Conduction Current Displacement Current It is defined as the actual current produced in the circuit due to the flow of electrons at an applied voltage. It is defined as the rate of change of the electric field between the plates of a capacitor at an applied voltage. It is produced due to the flow of charge carriers (electrons) uniformly whereas the electric field is constant with time It is produced due to the movement of electrons with the rate of change of electric field It accepts ohm’s law It doesn’t accept ohm’s law It is given as I = V/R It is given as It is represented as actual current It is represented as apparent current produced due to the electric field in a varying time The difference between conduction current and displacement current include the following.
• 15. Maxwell's equations:-
• 17. is no actual charge transfer in the insulated region between capacitor which is contradictory to the flow of current. Hence, displacement current is the current in the insulated region due to the changing electric flux. For a charged capacitor, electric field between the plates is given by: E= 𝑸 / 𝜺𝒐 ​A Q= 𝜺𝒐 ∅𝑬 Displacement current is given by: 𝒊𝒅​ = 𝒅𝑸 𝒅𝒕 ​= 𝜺𝒐 𝒅∅𝑬 𝒅𝒕 According to Maxwell's Ampere circuital Law, the line integral of magnetic field along a closed path is equal to μo times the total current. ∮B.dl= 𝝁𝒐 ​(𝒊𝒄​ ​+ 𝒊𝒅​ ​) where 𝒊𝒄 ​: Conduction current 𝒊𝒅 ​: Displacement current ∮B.dl= 𝝁𝒐 ​(𝒊𝒄 +𝜺𝒐 𝒅∅𝑬 ​) Displacement current
• 18. Relation between Displacement current and Conduction current :- For a charged capacitor, electric field between the plates is given b E= 𝑸 / 𝜺𝒐 ​A ∅𝑬 = E A = 𝑸 𝜺𝒐A ​​ A = 𝑸 𝜺𝒐 Conduction current is given by: 𝒊𝒄 = 𝒅𝑸 𝒅𝒕 Displacement current is given by: 𝒊𝒅 = 𝜺𝒐 𝒅∅𝑬 𝒅𝒕 = 𝜺𝒐 𝒅 𝒅𝒕 ​​ ( 𝑸 𝜺𝒐 ​​ ) = 𝒅𝑸 𝒅𝒕 = 𝒊𝒄
• 19. (Electromagnetic waves) 1.Electromagnetic waves are propagated by oscillating electric fields and magnetic field oscillation at right angles to each other. 2.These waves travel with speed 3×𝟏𝟎𝟖ms−1 in vacuum. 3.They are not deflected by electric or magnetic field. 4.They can show interference or diffraction. 5.They are transverse waves. 6.May be polarized. 7.Need no medium of propagation. 8.wavelength and frequency related as c=vλ. 9.The electromagnetic waves being chargeless.
• 23. Wavelength -A wavelength is the shortest distance between two adjacent crests or troughs of a transverse wave. For longitudinal waves, it is the distances between two adjacent compressions or rarefactions. Wavelength is measured in meter (m). wavelength in Angstrom unit [ Å ] 1 Å = 𝟏𝟎−𝟏𝟎 m Also, 1 nanometer = l nm = 10-9 m Frequency -The number of vibrations produced by a vibrating body in one second is called its frequency. Frequency is measured in units called hertz (Hz). When one wave passes in one second its frequency is 1 wave per second or 1 Hertz.
• 24. The Electric and Magnetic fields in EMR waves are always in phase and at 90 degrees to each other. In electronic signaling, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase as shown in Illustration A below. Phase can also be an expression of relative displacement between or among waves having the same frequency. Phase
• 25. Period -The last quantity we will consider is the period of a wave. A wave’s period is the length of time it takes for one wavelength to pass by a given point in space. Mathematically, the period (T) is simply the reciprocal of the wave’s frequency (f): T= 1 /f, The units of period are seconds (s). Amplitude -The amplitude of a wave is the mixture distance of the particles of the medium from the rest position. We can also say that it is the height of the crest or depth of a trough (transverse wave) measured from the rest position. Amplitude is measured in meters (m).
• 26. Speed, Wavelength, and Frequency The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This relationship is represented by the equation: Speed = Wavelength × Frequency The equation for wave speed can be rewritten as: Frequency=Speed/Wavelength Wavelength=Speed /Frequency
• 27. (Momentum):- The momentum of an EM wave is the energy carried by the wave divided by the speed of light. If an EM wave is absorbed by an object, or it reflects from an object, the wave will transfer momentum to the object. The longer the wave is incident on the object, the more momentum is transferred. (Poynting vector):- Poynting vector, a quantity describing the magnitude and direction of the flow of energy in electromagnetic waves. S.I. unit is watt per square meter. It is named after English physicist John Henry Poynting, who introduced it in 1884. S = E0 B0 / 2µ0 E = E0 / √2 B= B0 / √2 = E0 E0 / 2cµ0 B0 = E0 /c = E0 2 / 2cµ0 c 2 =1 / µ0 ε0 = cE0 2 / S = cE0 2 ε0/ 2 2c2µ0
• 28. Intensity of electromagnetic wave :- Intensity generally refers to a power per area (energy per area per time). For an electromagnetic wave, you can find its intensity by computing the magnitude of the Poynting vector. intensity I of an electromagnetic wave is proportional to E2 and B2. S.I. unit is 𝑾 /𝒎𝟐 . The energy of electromagnetic wave (U) crossing the area of cross section at P normally in time Δt is the energy of wave contained in a cylinder of length c Δt and area of cross section A. It is given by U = average energy density × Volume of cylinder U =uav (c Δt) A The intensity of electromagnetic wave at P is I = U / A Δt = uav c Δt A / A Δt = uav c In terms of maximum electric field uav = ε0 E0 2 / 2 so, I = ε0 E0 2 c / 2 = ε0 E2 rms c In terms of maximum magnetic field uav = B0 2 / 2μ0 so, I = B0 2 c / 2μ0 = B2 rms c / μ0 where c is the speed of light, ε0 is the permittivity of free space, and E0 is the maximum electric field strength E0/B0= c2 , where μ0 is the permeability of free space.
• 29. (Energy density) :-electromagnetic waves are three-dimensional, it is usually useful to discuss the energy density (energy per volume) of an electromagnetic wave. The total energy density of the electromagnetic wave is equal to the sum of the energy density of the electric field and the energy density of the magnetic field. Energy density due to electric field UE = E 2 ε0/ 2 Energy density due to magnetic field UB = B 2 / 2 µ0 आयाम क्रमशः E0 व B0 E = E0 / √2 B= B0 / √2 UE = E0 2 ε0/ 4 UB = B0 2 / 4 µ0 UE / UB = E0 2 ε0µ0/ B0 2 E0/B0= c2 =c2×1/ c2 ε0µ0 = 1/c2 UE / UB = 1 UE = UB The energy is carried by the
• 30. Regarding electromagnetic waves, both magnetic and electric field are equally involved in contributing to energy density Therefore, the formula of energy density is the sum of the energy density of the electric and magnetic field. UE = E 2 ε0 𝟐 UB = B 2 𝟐µ0 𝑼 = 𝑼𝑬 + 𝑼𝑩 𝑼 = E 2 ε0 𝟐 + B 2 𝟐µ0
• 31. (Radiation pressure):- An object absorbing an electromagnetic wave would experience a force in the direction of propagation of the wave. The force corresponds to radiation pressure exerted on the object by the wave. The force would be twice as great if the radiation were reflected rather than absorbed. perfectly absorbing perfectly reflecting
• 32. Hertz experiment The existence of electromagnetic waves was confirmed experimentally by Hertz in 1888. This experiment is based on the fact that an oscillating electric charge radiates electromagnetic waves. The energy of these waves is due to the kinetic energy of the oscillating charge. It consists of two metal plates A and B placed at a distance of 60 cm from each other. The metal plates are connected to two polished metal spheres S1 and S2 by means of thick copper wires. Using an induction coil a high potential difference is applied across the small gap between the spheres. s
• 33. Due to high potential difference across S1 and S2, the air in the small gap between the spheres gets ionized and provides a path for the discharge of the plates. A spark is produced between S1 and S2 and electromagnetic waves of high frequency are radiated. Hertz was able to produce electromagnetic waves of frequency about 5 × 107 Hz. Here the plates A and B act as a capacitor having small capacitance value C and the connecting wires provide low inductance L. The high frequency oscillation of charges between the plates is given by
• 34. (Electromagnetic spectrum) The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared light, ultraviolet light, X-rays and gamma-rays.
• 36. Gadi X U V In My Range Gamma rays X- ray Ultra-violet Rays Visible Rays Infra red Rays Microwave Radio waves How to learn
• 38. Type of Radiation Frequency Range (Hz) Wavelength Range gamma-rays 10 20 – 10 24 < 10 -3 nm x-rays 10 17 – 10 20 1 nm – 10 -3 nm ultraviolet 10 15 – 10 17 400 nm – 1 nm visible 4 – 7.5×10 14 700 nm – 400 nm infrared 10 13 – 10 14 1mm – 700 nm microwaves 3×10 11 – 10 13 0.1 m – 1mm radio waves < 3×10 11 > 0.1 m
• 39. How to remember Bade bhai ne Radio ko Koni se Mar kar Gira Diya jisse Chhota bhai hurt Ho Gaya . Red or Herschel ko ,new Drishya per uv ne writer Se Kaha Aise Rang Khel Ke Bekar Hain. Radio & TV - marconi - Bade bhai ne Radio ko Koni se Mar kar Gira Diya Microwaves - hertz - jisse Chhota bhai hurt Ho Gaya . Infrared - Herschel - Red or Herschel ko
• 40. Visible light - newton - new Drishya per Ultraviolet - Ritter - uv ne writer Se Kaha X-rays - Roentgen - Aise Rang Gamma rays - Becquerel - Khel Ke Bekar Hain
• 41. Radio waves Radio waves are used for communication such as television and radio. Radio waves are transmitted easily through air. They do not cause damage if absorbed by the human body, and they can be reflected to change their direction. These properties make them ideal for communications. Microwaves Microwaves are used for cooking food and for satellite communications. Infrared Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark. Security lights and remote controls for TV use infrared waves. Visible light Visible light is the light we can see. It is used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver. Ultraviolet We cannot see ultraviolet (UV) light but it can have hazardous effects on the human body. Ultraviolet light in sunlight can cause the skin to tan or burn and can also damage eyes. Fluorescent substances are used in energy-efficient lamps – they absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light.
• 42. •UV light is also used for banknote security and disinfecting water. •Most UV-B and all UV-C is absorbed by ozone (O3) molecules in the upper atmosphere. Consequently, 99% of the solar UV radiation reaching the Earth’s surface is UV-A. •An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. X-rays •X-rays have shorter wavelengths (higher energy ) than UV waves and, generally, longer wavelengths (lower energy) than gamma rays. Sometimes X-rays are called Röntgen radiation, after Wilhelm Röntgen, who is usually credited as their discoverer. •Because X-rays have very high energy they are known as ionizing radiation and can harm living tissue. A very high radiation dose over a short amount of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. •Lower doses of X-ray radiation can be very effectively used in medical radiography and X-ray spectroscopy. •X-rays are broken up into broad two categories: hard X-rays with energies above
• 43. •Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency and therefore high energy. •Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source. Gamma rays are usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus. Gamma rays
• 44. Radiation Production Detection Application Radio waves From oscillating electrical circuits. Accelerating charges Antennae (aerials), diodes, earphones. In telecommunication- radio broadcast, TV and satellite communication, cellular telephone, radar and navigation equipments etc. Microwaves From special vacuum tubes called magnetrons within microwave ovens. Accelerating charges & thermal agitation Crystal detectors, solid state diodes, antennae. Cooking in microwave cookers. In communication- mobile phones. In speed cameras. Infra red From thermal vibration of atoms in very hot bodies. Eg- the sun. Thermal agitations & electronic transitions Thermopile, bolometer, thermometer, photographic film. Heating effect on the skin. Burglar alarms, in military night vision missiles, cooking, heating and drying of grains, in green housing, in remote controls for TVs and VCD/DVDs, in photography.
• 45. Visible light Sun, hot objects, lamps, laser beams. Thermal agitations & electronic transitions The eye, photographic film, photocell. Vision (sight), photography, photosynthesis and optical fibre. Laser beams used in laser printers, weapon aiming systems, CD players. Ultraviolet The sun, sparks, mercury vapour lamps. Thermal agitations & electronic transitions Photographic film, photocells, fluorescent materials e.g quinine sulphate. Detection of forgeries, skin treatment and killing of bacteria, spectroscopy and mineral analysis, making of clothes and a source of vitamin D. X-rays In X-ray tubes Inner electronic transitions and fast collisions Fluorescent screen and photographic film. Radiography (identification of internal body structures or bones), cancer therapy, crystallography (study of crystal structure), pest and germ
• 46. Gamma radiation Emitted by radioactive substances. Nuclear decay Radiation detectors e.g GM tube. Sterilizing medical equipment and food. Killing of cancer cells and other malignant growths. Pest control. Detection of flaws in metals.
• 47. Waves which are not electromagnetic waves :- a) Cathode rays b) X-rays c) Beta rays d) Cosmic rays