Osm Physics by Ashish

  Young’s Double Slit Experiment, Types of fringes According to Huygens’ principle , every point on a wavefront acts as a source of secondary wavelets. In Young’s experiment, light from a monochromatic source illuminates two narrow slits S 1 S_1 ​ and S 2 S_2 ​ .  These two slits behave as coherent sources because the waves emerging from them have: The same frequency A constant phase difference The same wavelength When the waves from S 1 S_1  and S 2 S_2 ​ overlap on the screen, they produce interference fringes consisting of alternate bright and dark bands. When two waves travel through the same medium simultaneously, the resultant displacement at any point is equal to the algebraic sum of the individual displacements produced by each wave. If the displacements due to two waves are: y 1 = a 1 sin ⁡ ω t and y 2 = a 2 sin ⁡ ( ω t + ϕ ) y_2=a_2\sin(\omega t+\phi) then, according to the principle of superposition: y = y 1 + y 2 \boxed{y=y_1+y_2} where y is ...

  Huygens' Principle (also called the Huygens–Fresnel Principle ) is a fundamental concept in wave optics proposed by the Dutch physicist Christiaan Huygens in 1678. It provides a geometric method for understanding wave propagation. The Principle Every point on a wavefront can be considered a source of secondary spherical wavelets (called secondary wavelets ). The new wavefront at a later time is the envelope of all these secondary wavelets. Key Concepts Primary Wavefront – The original advancing wave surface. Secondary Wavelets – Each point on the primary wavefront acts as a new point source, emitting tiny spherical waves in all directions. Envelope – The tangent surface (envelope) that touches all secondary wavelets at a given later instant forms the new wavefront .

Interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have a greater amplitude or a lower amplitude if the two waves are in phase or out of phase, respectively. Coherent sources of light If the phase difference the waves from two sou sources reaching any point in space does not change with time rather it remains constant then these sources of light are known as 'coherent sources of light'. This property of the waves is known as coherence .  A wave which appears to be a pure sine wave for an infinitely large period of time or in an infinitely extended space is said to be a perfectly coherent wave. Thus there are two different criteria of coherence. (i) Temporal coherence and (ii) Spatial coherence. (i) Temporal Coherence Definition: Temporal coherence refers to the correlation between the phase of a wave at a given instant of time.  It is a me...