Physics

• The law of conservation of energy states that energy cannot be created nor destroyed but only transformed into different forms.
• Displacement current is a current produced in a region where the electric field and electric flux change with time
• Ampere-Maxwell Law states that the permeability (μo) is equal to 4π * 10^-7 V/Am
• Maxwell's Equations include the Ampere-Maxwell law
• Electromagnetic waves have electric and magnetic field vectors that change sinusoidally and are perpendicular to each other and to the direction of wave propagation
• Properties of EM Waves:

  • Transverse in nature
  • Propagate through space at the speed of light (3 * 10^8 m/s)
  • Speed of EM wave (c) = 1 / √(μo * εo)
  • Total radiant flux produced by accelerated charged particles is given by p = q^2a^2 / 6πεoc^2
  • Rate of flow of energy in EM wave is described by the Poynting vector (S = 1/μo * E * B)
  • Intensity of EM wave is defined as energy crossing per unit area per unit time perpendicular to the wave propagation
  • Hertz confirmed the existence of electromagnetic waves in 1888
• Propagation of electromagnetic waves involves transmission from a transmitter antenna to a receiving antenna in radio wave communication
• Electromagnetic Spectrum is the array of electromagnetic radiations in order of wavelength or frequency

  • Radio and microwaves are used in radio and TV communication
  • Infrared rays are used for various purposes like treating muscular strain and weather forecasting
  • Ultraviolet rays are used in studying molecular structure and sterilizing surgical instruments
  • X-rays are used in detecting faults in metal products and studying crystal structure
  • Gamma rays are used for studying nuclear structure
• Earth's Atmosphere:

  • Troposphere extends up to 12 km
  • Stratosphere extends from 12 km to 50 km, containing the ozone layer
  • Mesosphere extends from 50 km to 80 km
  • Ionosphere extends from 80 km to 400 km, with layers like D, E, F1, and F2
• • Antennas convert electrical energy into electromagnetic waves for transmission and reception
• Communication is the faithful transmission of information from one place to another

  • Communication system includes a transmitter, communication channel, and receiver
  • Analog signals vary continuously with time, while digital signals have only two values
  • Modulation is the process of superimposing audio signal over a high frequency carrier wave
  • Types of modulation include Amplitude Modulation, Frequency Modulation, and Pulse Modulation
  • Demodulation is the process of separating audio signal from modulated signal
• Demodulation is the process of extracting the original signal from a modulated signal
• An antenna converts electrical energy into electromagnetic waves at the transmitting end and picks up transmitted signals at the receiving end
• A modem is a device that can modulate and demodulate signals, connecting one computer to another through ordinary telephone lines
• Fax (Facsimile Telegraphy) is the electronic reproduction of a document at a distant place
• Radio waves are electromagnetic waves with a frequency ranging from 500 kHz to about 1000 MHz, used in radio communication
• Propagation of Radio Waves:

  • Ground Wave or Surface Wave Propagation: suitable for low and medium frequencies up to 2 MHz, used for local broadcasting
  • Sky Wave Propagation: suitable for radio waves of frequency between 2 MHz to 30 MHz, used for long-distance radio communication
  • Space Wave Propagation: suitable for 30 MHz to 300 MHz, used in television and radar communication, also known as line of sight communication
• Critical Frequency is the highest frequency of radio wave that can be reflected back by the ionosphere
• Skip Distance is the minimum distance from the transmitter at which a sky wave of a frequency but not more than the critical frequency is sent back to the earth
• Fading is the variation in the strength of a signal at the receiver due to interference of waves
• Microwaves are electromagnetic waves of frequency 1 to 300 GHz, used in radar communication and have a wavelength of a few mm
• Satellite Communication is carried out between a transmitter and a receiver through a geostationary satellite, providing wide coverage and used effectively in mobile communication
• Merits of Satellite Communication:

  • Wide coverage range
  • Effective in mobile communication
  • Economical compared to other communication systems
  • Cost-effective in remote and hilly areas
  • Permits transmission of data at a high rate
  • Accurate and economical for search, rescue, and navigation purposes
• Demerits of Satellite Communication:

  • Difficult to repair if a system on the satellite goes out of order
  • Time delay between transmission and reception due to large communication path length
• Remote Sensing is a technique of observing or measuring the characteristics of an object at a distance, utilizing a polar satellite
• LED and Diode Laser are preferred sources for optical communication links due to their features like producing suitable power, monochromatic and coherent light
• Optical Fibres are long threads consisting of a central core of glass or plastic surrounded by a cladding, used in various applications like transmission of electrical signals and medical examinations
• Power = rate at which energy is used/produced (W)