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Questions and Answers
In thin film interference, what path difference results in constructive interference (bright film) in reflected light, considering a phase change of $\lambda/2$?
In thin film interference, what path difference results in constructive interference (bright film) in reflected light, considering a phase change of $\lambda/2$?
- $2 \mu t \cos r = n \lambda$
- $2 \mu t \cos r = (2n - 1) \lambda / 2$
- $2 \mu t \cos r = (2n + 1) \lambda / 2$ (correct)
- $2 \mu t \cos r = (n + 1) \lambda$
If a thin film with refractive index $\mu$ and thickness $t$ is illuminated at an angle $r$, what is the optical path difference between two light rays reflected from the top and bottom surfaces, excluding phase change?
If a thin film with refractive index $\mu$ and thickness $t$ is illuminated at an angle $r$, what is the optical path difference between two light rays reflected from the top and bottom surfaces, excluding phase change?
- $2 \mu t \cos r$ (correct)
- $2 \mu t$
- $2t \cos r$
- $ \mu t \cos r$
In Newton's rings experiment, why is the center of the ring pattern dark when viewed in reflected light?
In Newton's rings experiment, why is the center of the ring pattern dark when viewed in reflected light?
- Due to constructive interference at the center.
- Because the thickness of the air film is equal to $\lambda$ at the center.
- Due to destructive interference and a path difference of $\lambda/2$. (correct)
- Due to destructive interference and a path difference of $\lambda/4$.
In the context of Newton's rings, what does the radius of the $n^{th}$ dark ring depend on?
In the context of Newton's rings, what does the radius of the $n^{th}$ dark ring depend on?
For Newton's rings formed by reflected light, how are the diameters of the dark rings related to natural numbers?
For Newton's rings formed by reflected light, how are the diameters of the dark rings related to natural numbers?
What happens to the fringe width in Newton's rings as the order of the fringe increases?
What happens to the fringe width in Newton's rings as the order of the fringe increases?
In the experiment to determine the wavelength of sodium light using Newton's rings, what parameters are directly measured to calculate the wavelength?
In the experiment to determine the wavelength of sodium light using Newton's rings, what parameters are directly measured to calculate the wavelength?
During the determination of the refractive index of a liquid using Newton's rings, how does introducing the liquid affect the ring diameters?
During the determination of the refractive index of a liquid using Newton's rings, how does introducing the liquid affect the ring diameters?
What is the primary difference between interference due to division of wavefront and division of amplitude?
What is the primary difference between interference due to division of wavefront and division of amplitude?
In Fresnel's biprism experiment, what is the function of the biprism?
In Fresnel's biprism experiment, what is the function of the biprism?
In the experimental setup for Fresnel's biprism, what adjustments are crucial for observing clear interference fringes?
In the experimental setup for Fresnel's biprism, what adjustments are crucial for observing clear interference fringes?
What is the effect of lateral shift in Fresnel's biprism experiment, and how is it corrected?
What is the effect of lateral shift in Fresnel's biprism experiment, and how is it corrected?
In Fresnel's biprism experiment, what does the fringe width, $\beta$, represent?
In Fresnel's biprism experiment, what does the fringe width, $\beta$, represent?
Which of the following is NOT a required measurement when determining the wavelength of light using Fresnel's biprism?
Which of the following is NOT a required measurement when determining the wavelength of light using Fresnel's biprism?
In thin-film interference, what condition changes when the film is observed at an angle instead of head-on?
In thin-film interference, what condition changes when the film is observed at an angle instead of head-on?
How does coating lenses with thin films reduce reflections?
How does coating lenses with thin films reduce reflections?
What is the effect of using white light in Newton's rings experiment?
What is the effect of using white light in Newton's rings experiment?
When determining the radius of curvature of a plano-convex lens using a spherometer, what measurements are required?
When determining the radius of curvature of a plano-convex lens using a spherometer, what measurements are required?
In transmitted light Newton's rings, what condition applies for bright rings?
In transmitted light Newton's rings, what condition applies for bright rings?
How do the diameters of the bright rings change when Newton's Rings apparatus is immersed in a liquid of refractive index $\mu$?
How do the diameters of the bright rings change when Newton's Rings apparatus is immersed in a liquid of refractive index $\mu$?
Flashcards
Path difference in thin films
Path difference in thin films
The path difference between two reflected light rays in a thin film is given by (Δ = μ(BC + CD) - BE), where (μ) is the refractive index of the film, BC and CD are the paths in the film, and BE is the path in air.
Condition for Brightness
Condition for Brightness
Maxima occur in reflected light when (2μt cos r = (2n + 1)λ/2), where (μ) is the refractive index, (t) is the thickness of the film, (r) is the angle of refraction, (n) is an integer, and (λ) is the wavelength of light.
Condition for Darkness
Condition for Darkness
Minima occur in reflected light when (2μt cos r = nλ), where (μ) is the refractive index, (t) is the thickness, (r) is the angle of refraction, (n) is an integer, and (λ) is the wavelength of light.
Newton's Rings
Newton's Rings
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Central Spot
Central Spot
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Division of Wavefront
Division of Wavefront
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Division of Amplitude
Division of Amplitude
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Fringe Width
Fringe Width
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Biprism Adjustments
Biprism Adjustments
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Wavelength Determination
Wavelength Determination
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Study Notes
- Interference occurs when light waves combine, leading to phenomena like bright and dark fringes
Interference in Thin Films
- Interference in thin films arises from light reflecting off the top and bottom surfaces of the film
- The effective path difference decides the type of interference
- Phase change of π (equivalent to λ/2 path difference) happens when light reflects from a denser medium's surface
- Effective path difference between reflected rays is (2µt cos r±λ/2), where:
- µ is refractive index
- t is film thickness
- r is angle of refraction
Constructive Interference
- For maxima (bright reflection), the condition is 2µt cos r = (2n + 1) λ/2, where n is an integer
Destructive Interference
- For minima (dark reflection), the condition is 2µt cos r = nλ
Newton's Rings Setup
- Newton's rings are formed by placing a plano-convex lens on a glass plate, creating an air film of increasing thickness
- When monochromatic light falls on the lens, a pattern of concentric dark and bright rings appears in reflected light
- The rings are due to the interference between light waves reflected from the top and bottom surfaces of the air film
Theory of Newton's Rings (Reflected Light)
- For bright rings, 2t = (2n - 1) λ/2
- For dark rings, 2t = nλ, where n is an integer
- Radius r of the Newton's ring is related to the film thickness via r² = 2Rt, where R is the radius of curvature
- Diameter D of the nth bright ring is D = √(2λR(2n - 1))
- Diameters of bright rings are proportional to the square roots of odd natural numbers
- Diameter D of the nth dark ring is D = 2√(nλR)
- Diameters of dark rings are proportional to the square roots of natural numbers
Fringe Width
- Fringe width decreases as the order of the fringe increases
Transmitted Light
- With transmitted light, the central ring is bright, which is the opposite of the rings in reflected light
Determining Wavelength
- λ can be destermined as λ = (Dn+p² - Dn²)/4pR;
- R is curvature radius
- Dn and Dn+p are nth and (n+p)th ring diameters
Determining Refractive Index of Liquid
- The experiment is repeated with liquid between lens & plate. You simply solve for µ
- µ = (Dn+p² - Dn²)/(D'n+p² - D'n²), where D are radius without liquid and D' with liquid
Types of Interference:
- Division of wavefront: Wavefront splits via reflection, refraction, or diffraction (ex: Fresnel Biprism)
- Division of amplitude: Amplitude splits via reflection or refraction (ex: Newton's Rings)
Fresnel's Biprism:
- Biprism creates two coherent images from a single slit. The images act as coherent sources
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