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INTERFERENCE OF LIGHT. Interference is the phenomenon in which two waves superpose to form the resultant wave of the lower, higher or same amplitude. The most commonly seen interference is the optical interference or light interference. This is because light waves are randomly generated every which way by most sources. This means that light waves coming out of a source do not have a constant amplitude, frequency or phase ..

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COHERENT SOURCES OF LIGHT. Two sources are called as coherent sources of light if they have same phase difference that does not change with respect to time. A coherent source forms sustained interference patterns when superimposition of waves occur and the positions of maxima and minima are fixed. Laser light can be treated as coherent sources because if emits lights with almost same frequency..

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NON COHERENT SOURCES OF LIGHT. Incoherent sources are those which sources of light which emit waves that have random frequencies and phase differences. There is no relationship between the waves in terms of frequencies and phase difference. For example:-Electric bulb, night lamp..

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INTENSITY OF LIGHT. Intensity is directly related to Brightness. :- More brightness ( more intensity of light). :- Low brightness ( low intensity of light ). The more photons emitted per unit time, the greater the intensity of the light. The less Photons emitted per unit time, the lesser the intensity of the light..

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YOUNGS DOUBLE SLIT EXPERIMENT. Young’s double-slit experiment uses two coherent sources of light placed at a small distance apart, usually, only a few orders of magnitude greater than the wavelength of light is used. Young’s double-slit experiment helped in understanding the wave theory of light which is explained with the help of a diagram.

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Position of Bright Fringes. For maximum intensity or bright fringe to be formed at P Path difference, Δz = nλ (n = 0, ±1, ±2, . . . .) i.e., Yd/D = nλ or Y= nλD/d The distance of the nth bright fringe from the centre is Yn = nλD/d Similarly, the distance of the (n-1)th bright fringe from the centre is Y (n-1)= (n -1)λD/d Fringe width, β = Yn – Y (n-1) = nλD/d – (n -1)λD/d = λD/d (n = 0, ±1, ±2, . . . .).

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Position of Dark Fringes. For minimum intensity or dark fringe to be formed at P, Path difference, Δ z = (2n + 1) ( λ/2) ( n = 0, ±1, ±2, . . . .) i.e., Y = (2n +1) λ D/2d The distance of the nth dark fringe from the centre is Yn = (2n+1) λ D/2d Similarly, the distance of the (n-1)th bright fringe from the centre is Y (n-1)= (2(n-1) +1) λ D/2d Fringe width, β = Yn – Y (n-1) = (2n + 1) λ D/2d – (2(n -1) + 1) λ D/2d = λ D/d Here, (n = 0, ±1, ±2, . . . .).

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Fringe Width. Distance between two adjacent bright (or dark) fringes is called the fringe width. β = λD/d If the apparatus of Young’s double slit experiment is immersed in a liquid of refractive index (μ), then the wavelength of light and fringe width decreases ‘μ’ times. if white light is used in place of monochromatic light, then colored fringes are obtained on the screen with red fringes larger in size than violet..

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What if we use white light in the setup of YDSE. There will be the brightest spot at the centre because path difference will be zero, and interference will be constructive interference but above or below the central bright , we may have maxima or minima for individual color individually. Basically, we will not have a definite color . It may be Blueish, Greenish, Or may be any other color..

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HUYGEINS PRINCIPAL. Huygens Principle, also known as the Huygens–Fresnel principle highlights the following wave propagation behavior: Wave fronts will be perpendicular to the direction of propagation of wave. At any given point in time, the common tangent on the wavelets in the forward direction gives the new wavefront. The wavefront is the sum of the spherical wavelets.

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Advantages and Disadvantages of Huygens Principle.

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REFLECTION. When a ray of light falls on any object (polished, smooth, shiny object), light from that object bounces back those rays of light to our eyes and this is known as “Reflection” or “Reflection of Light”. For example, twinkling of stars or light reflected by a mirror..

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LAWS OF REFLECTION. The first law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror, all lie in the same plane. The second law of reflection states that the angle of reflection is equal to the angle of incidence. Both angles are measured with respect to the normal to the mirror..

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REFRACTION. Refraction is the bending of a wave when it passes from one medium to another. The bending is caused due to the differences in density between the two substances..

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LAWS OF REFRACTION. The incident ray refracted ray, and the normal to the interface of two media at the point of incidence all lie on the same plane. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. This is also known as Snell’s law of refraction..

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Refraction of Light in Real Life. Mirage and looming are optical illusions which are a result of refraction of light. A swimming pool always looks shallower than it really is because the light coming from the bottom of the pool bends at the surface due to refraction of light. Formation of a rainbow is an example of refraction as the sun rays bend through the raindrops resulting in the rainbow. When white light passes through a prism it is split into its component colours – red, orange, yellow, green, blue and violet due to refraction of light..

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Applications of Refraction of Light. Refraction has many applications in optics and technology. A few of the prominent applications are listed below: A lens uses refraction to form an image of an object for various purposes, such as magnification. Spectacles worn by people with defective vision use the principle of refraction. Refraction is used in peepholes of house doors, cameras, movie projectors and telescopes..

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