Unit 2 – Nature of Light - Class 11 Chemistry Online Notes

Unit 2 – Nature of Light - Class 11 Chemistry Online Notes

Wave Nature of Light

The wave properties of light (electromagnetic radiation) are described in terms of the following parameters:

1. Frequency (ν, spell as mu, in Greek): The frequency of a wave is the number of cycles it undergoes per second. Its unit is 1/second (sec-1, it is also called Hertz, Hz)
2. Wavelength (λ, termed as lambda in Greek): The wavelength is the distance between any points on the wave and the corresponding point on the next crest or trough of the wave. It is the distance the wave travels during one cycle. The units of wavelength are meters (m), for very short distances it is nanometers (10-9m), picometers (10-12m) or non-SI unit is Angstrom (Å, 10-10m).
3. Speed: The speed of the wave is the distance it moves per unit time i.e. meters per second (m/s). It is the product of frequency (cycles per second) and wavelength (meters per cycle).
In a vacuum, the electromagnetic radiations move at 3.00x 108m/s and it is constant, represented as the speed of light, c. Thus c = ν x λ
Since c is constant, therefore ν and λ have a reciprocal relationship. The radiations with high frequency have low wavelength and vice versa.
4. Amplitude: It is the height of the crest or depth of troughs. For electromagnetic waves, the amplitude is related to the intensity of the radiation. It is the measure of brightness of the visible light. Light of low amplitude means it is less intense and dim, while the light of high amplitude means it is more intense and bright.

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