Q47 of 69 Page 65

Neon gas is generally used in the sign boards. If it emits strongly at 616 nm, calculate (a) the frequency of emission, (b) distance travelled by this radiation in 30 s (c) energy of quantum and (d) number of quanta present if it produces 2 J of energy.

Given:

Wavelength, λ = 616 nm = 616× 10-9m


To find frequency:


Speed of Light = [Frequency] × [Wavelength]


We know speed of light = 3×108 m/s


Frequency, v = [3×108] / [616 × 10-9]


v = 4.87×1014 Hz


To find distance travelled:


Velocity of the radiation = 3× 108 m/s


Therefore, distance travelled in 30s = 30× 3× 108 = 9.0× 109m


To find the energy:


By Planck’s relation we have,


Energy, E = h×v


= [6.626×10-34] × [4.87×1014]


= 3.23×10-19 J


Therefore, the energy of the photon corresponding to light of frequency 4.87×1014 Hz is 3.23×10-19 J.


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