Explain the Doppler Effect of light? Based on NCERT Class 12 Wave Optics.
The Correct Answer and Explanation is:
Doppler Effect of Light (Based on NCERT Class 12 Wave Optics)
The Doppler Effect of light refers to the change in the observed frequency or wavelength of light due to the relative motion between the source of light and the observer. When the source and observer are moving toward each other, the observed frequency increases, and the wavelength appears shorter. When they move apart, the observed frequency decreases, and the wavelength appears longer.
In simple terms, this effect helps explain why light from approaching objects appears blue-shifted (shifted toward the blue or shorter wavelength end of the spectrum), while light from receding objects appears red-shifted (shifted toward the red or longer wavelength end of the spectrum).
Mathematical Expression:
For light waves, the Doppler Effect is given by:
Observed frequency (f’) = f × (c ± v₀) / (c ± vₛ)
Where:
- f’ is the observed frequency
- f is the actual frequency of the source
- c is the speed of light
- v₀ is the speed of the observer (positive if moving toward the source)
- vₛ is the speed of the source (positive if moving away from the observer)
For most practical cases in astronomy or high-speed situations, a more general relativistic formula is used, but for small velocities compared to the speed of light, the classical approximation provides useful insights.
Explanation:
The Doppler Effect of light has significant applications in astronomy. Scientists use this effect to determine whether distant stars or galaxies are moving toward or away from Earth. A blue-shift indicates that the object is approaching, while a red-shift suggests the object is receding.
The discovery of red-shift in light from distant galaxies supports the idea that the universe is expanding, forming the basis of Hubble’s Law. Thus, the Doppler Effect of light is not only a fundamental concept in optics but also a crucial tool for understanding the universe.
