Interference In Thin Films
- What are the conditions for bright and dark fringes in reflected light from a thin film? In one line In reflected light from a thin film, brightness occurs when 2μ tcos r = (2n-1)λ/2 and darkness when 2μ tcos r = nλ . Explained s... 1
- How does interference occur in a thin film of uniform thickness, and what is the path difference? In one line Light reflected from the top and bottom surfaces of a thin film comes from the same wave (division of amplitude), so the two ref... 1
- How are interference fringes formed in a wedge-shaped thin film and what is the fringe width? In one line A wedge-shaped film has thickness increasing steadily from the edge, so each fringe follows a line of constant thickness, giving... 1
- How are Newton's rings formed and why is the central spot dark in reflected light? In one line Newton's rings are concentric circular fringes formed by interference in the air film between a plano-convex lens and a flat gla... 1
- How are Newton's rings used to find the wavelength of monochromatic light? In one line By measuring the diameters of two dark rings that are p rings apart and knowing the lens radius R , the wavelength is found from... 1
- How are Newton's rings used to find the refractive index of a transparent liquid? In one line Filling the gap between the lens and plate with a liquid shrinks the rings by a factor √(μ) , so the refractive index is the rat... 1
- How does an anti-reflecting coating work and what thickness and refractive index should it have? In one line An anti-reflecting coating is a thin transparent film of quarter-wave optical thickness whose two reflected beams cancel by dest... 1
- Obtain the condition for maxima and minima of the light reflected from a thin transparent film of uniform thickness. Set-up: A thin transparent film of uniform thickness t and refractive index μ is in air. A ray AB is incident at angle i . Part of it is ref... 1
- What is antireflection coating? What should be the refractive index and minimum thickness of the coating? Antireflection (AR) coating: A thin transparent film, for example MgF₂, deposited on a lens or glass surface. Light reflected from its upper... 1
- In Newton’s rings experiment the diameter of 5th ring was 0.336 cm and the diameter of 15th ring was 0.590 cm. Find the radius of curvature of plano convex lens if the wavelength of light used is 5890 Å. Given: D₅=0.336 cm, D₁₅=0.590 cm, so p = 10. λ=5890 Å =5.89×10⁻⁷ m. Air film (μ = 1). Formula: D_(n+p)²-D_n²=4pλ R⇒ R=dfracD_(n+p)²-D_n²4pλ... 1
- Find the minimum thickness of soap film which appears dark (Wavelength [first digit partly illegible in the source scan; read as 5]896 A°) in reflection when light is incident normally on the film. Given refractive index of the film is 1.33. Assumption: The first digit of the wavelength is obscured in the scan. We take λ=5896 Å (the sodium D-line). Given: λ=5.896×10⁻⁷ m, μ=1.33 ,... 1
- Obtain an expression for minimum thickness of anti-reflecting film. Anti-reflecting (AR) film: A thin transparent film of index μ and thickness t coated on glass of index μ_g , with 1<μ<μ_g . R1 R2 incident (... 1
- Derive the condition for maxima due to interference of light reflected from thin film of uniform thickness. Set-up: A thin transparent film of uniform thickness t and refractive index μ is in air. A ray AB is incident at angle i . Part of it is ref... 1
- Explain why an excessively thin film appears black in reflected light? For a thin film of index μ and thickness t , the effective path difference between the two reflected rays is Δ=2μ tcos r-λ/2 The extra λ/2 c... 1
- In a Newton’s ring arrangement, a drop of liquid of refractive index 1.33 is placed in between the lens and plate. The diameter of 9th dark ring is found to be 0.58 cm. Obtain the radius of curvature, if the wavelength of light is 6000 A°. Given: μ=1.33 , n=9 , D₉=0.58 cm =5.8×10⁻³ m, λ=6000 Å =6×10⁻⁷ m. Formula: For dark rings in reflected light with a liquid film, 2μ t=nλ and... 1
- With the experimental set up of Newton’s ring, explain the determination of refractive index of a liquid. Experimental set-up: travelling microscope | v S (sodium lamp)--> L (lens) --> G (glass plate at 45°) | reflects light down v ( plano-convex... 1