If the diameter of a carbon atom is 0.15 nm, calculate the number of carbon atoms which can be placed side by side in a straight line across length of scale of length 20 cm long.
Diameter of carbon atom  = 0.15 nm
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Length along which carbon atoms are to be placed
              = 20 cm
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Hence, number of carbon atoms which can be placed along the length
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Here c = 3.00 x 108 ms-1;
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This is the characteristic radio wave-length.
The frequency of D-line in the spectrum of sodium is 5.09 x 1014s-1. Calculate the wavelength of light.
Frequency of radiation
               = 5.09 x 1014 s-1
Velocity of light  = 3 x 108 ms-1
We know, Â Â Â
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or            Â
A 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 radiostation emitted.
v = 920 kHz = 920 x 103Â Hz = 920 x 103Â s-1
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or      Â
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 Wavelength of radiowave broadcast by the station = 326 m
Isotopes of an element have similar chemical properties and isobars have different chemical properties. Explain.
Isotopes of an element have same number of electrons and protons but have different number of neutrons. Since chemical properties of elements depend upon atomic number, isotopes of an element have similar chemical properties.
On the other hand, isobars have different number of electrons, protons as well as neutrons. Thus, isobars have different chemical properties.