Long Answer TypeCalculate the frequency and wavelength of light of wavelength:
(i) 5000 A (ii) 4.4 mμ (iii) 580 mm
Short Answer TypeA certain radiostation broadcasts on a frequency of 920 k Hz. What is the wavelength of electromagnetic radiation broadcast by the radio station?
The frequency of D-line in the spectrum of sodium is 5.09 x 1014s-1. Calculate the wavelength of light.
The wavelength range of the visible spectrum extends from violet (400 nm) to red (750 nm). Express these wavelengths in frequencies (Hz). [1 nm = 10-9 m]
Calculate the wavelength, frequency and wave number of light wave whose period is 2.0 x 10-10 s
Yellow light emitted from a sodium lamp has a wave length (λ) of 580 nm (or 5800Å). Calculate the frequency (v) and wave number ⊽ of the yellow light.
Long Answer TypeShort Answer TypeLong Answer TypeWhat is an emission spectra? What are its types?
When the radiation emitted from some source e.g. from the sun or by passing electric discharge through a gas at low pressure or by heating some substance to high temperature etc. is passed directly through the prism and recorded over a photographic plate or screen, the spectrum obtained is known as an emission spectrum.
Types of an emission spectrum. Emission spectra can be further divided into three types:
(i) Continuous spectrum. When white light from the sun or an electric bulb is analysed by passing through a prism, the spectrum obtained consists of a continuous band of seven colours from red to violet (like a rainbow). Such a spectrum is known as continuous spectrum. In such a spectrum, there is a continuous sequence of impressions in the form of colours.
(ii) Line spectrum. When the radiations emitted by the excited substances e.g. by placing some volatile salt (say NaCl) in the bunsen flame or by
passing an electric discharge through a gas at low pressure are analysed by a spectrograph, discontinuous spectra consisting of a series of sharp lines and separated by dark bands is obtained. Such a spectrum consisting of parallel lines separated by dark space is called line spectrum. Line spectra is a finger -print of atoms because :
(a) each element has its characteristic spectrum, differing from those of all other elements and
(b) each line in the spectrum corresponds to a particular wavelength.
(iii) band spectrum. A molecule (unlike the atom) emits the radiations over a close range of wavelengths so that the spectrum consists of the group of lines spaced very close together. These lines are so much close that they look like a band. Such a spectrum is known as band spectrum.
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