Coherence in Light Waves

Coherence refers to the property of light waves where they exhibit a constant phase difference and have the same wavelength. When two light sources are coherent, it means that the waves they produce are in perfect sync with each other. Coherent light waves have a consistent pattern of constructive and destructive interference, which leads to various phenomena like interference, diffraction, and polarization.

Explanation of the Correct Answer

The correct answer to the question is option 'B', which states that two sources of light are coherent when they give out light waves of the same wavelength and a constant phase difference. Let's understand why this answer is correct.

Same Wavelength
When two light waves have the same wavelength, it means that the distance between corresponding points on each wave, such as two adjacent crests or troughs, is the same. This characteristic is crucial for coherence because it determines how the waves interact with each other. If the wavelengths are different, the waves will not have a consistent pattern of interference, leading to a lack of coherence.

Constant Phase Difference
Phase refers to the position of a point on a wave cycle relative to a reference point. It is usually measured in degrees or radians. The phase difference between two coherent light waves remains the same over time. This means that the crests and troughs of the waves align perfectly, resulting in constructive interference. Constructive interference occurs when waves are in phase and their amplitudes add up, creating regions of maximum brightness.

Importance of Coherence
Coherence is crucial for various applications in optics, such as holography, interferometry, and telecommunications. In holography, coherent light waves are used to create interference patterns that record and reconstruct three-dimensional images. Interferometry utilizes coherence to measure small displacements, distances, and surface irregularities with high precision. In telecommunications, coherent light sources are used for long-distance transmission of information through optical fibers.

Conclusion
In summary, coherence in light waves is achieved when two sources emit waves with the same wavelength and a constant phase difference. This property enables the waves to exhibit a consistent pattern of interference, leading to various applications in optics. Understanding coherence is essential for comprehending phenomena like interference, diffraction, and polarization in the field of optics.