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Wave nature of Electromagnetic Radiation, The important characteristics of these radiations are:, 1. The oscillating electric and magnetic fields are perpendicular to each other and both are, perpendicular to the direction of propagation of the wave., 2. The electromagnetic waves do not require a medium for propagation and can move in, vacuum., 3. Electromagnetic radiations can be represented by different types of units such as wave, length,frequency,amplitude atc…., 4. Arrangement of electromagnetic radiations based on frequency and wavelength is called, electro magnetic spectrum, 5. Energy of electromagtnetic raqdiation directly proportional to frequency., 6. The frequency (ν ), speed of light (c) and the wave length (λ)are related to each other as:, c = ν λ, 7. All electromagnetic radiation travel through vacuum with a constant speed of 3x10 8 m/s., Some important terms relating to electromagnetic radiations, 1. Frequency (ν ): It is defined as the number of waves that pass through a given point in, one second. The SI unit for frequency is hertz (Hz, s–1)., 2. Wavelength (λ) : It is the distance between two adjacent crusts or two adjacent troughs., Its unit is m or cm., 3. Wave number (ῡ ): It is defined as the number of wavelengths per unit length. It is the, reciprocal of wavelength. Its unit is m–1 or cm-1., Particle Nature of Electromagnetic Radiation: Planck’s Quantum Theory, Atoms and molecules could emit (or absorb) energy not in a continuous manner, but, discontinuously insmall packets of energy called quanta or photons., The energy (E ) of a quantum of radiation is proportional to its frequency (ν ), It is expressed by the equation, E = hν, Where ‘h’ is known as Planck’s constant and its value is 6.626×10–34 J s., Line Spectrum of Hydrogen, When an electric discharge is passed through gaseous hydrogen, the H2 molecules dissociate and, theenergetically excited hydrogen atoms produced emit electromagnetic radiation of discrete, frequencies. Thehydrogen spectrum consists of several series of lines named after their, discoverers. The first five series of linesare Lyman, Balmer, Paschen, Brackett and Pfund, series. Among these lines, the Balmer series is the only seriesthat we can be visible (since it lies, in the visible region of emr)., Series, Lyman, Balmer, Paschen, Brackett, Pfund, , -, , Spectral region, Ultra violet, Visible, Infra red, Infra red, Infra red