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NATURE OF LIGHT

NATURE OF LIGHT. TRANSVERSE NATURE. Fermat's principle. "Light, in going between two points, traverses the route having the smallest optical path length – smallest time taken.". Huygens’ Principle.

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NATURE OF LIGHT

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  1. NATURE OF LIGHT TRANSVERSE NATURE

  2. Fermat's principle "Light, in going between two points, traverses the route having the smallest optical path length – smallest time taken."

  3. Huygens’ Principle A typical statement of the principle is “every point on a wavefront acts as a source of a new wavefront, propagating radially outward.”

  4. Law of Reflection Law of Refraction Snell’s Law

  5. Critical Angle Light bends toward the normal when the light enters a medium of greater refractive index, and away from the normal when entering a medium of lesser refractive index. As you approach the critical angle the refracted light approaches 90° and, at the critical angle, the angle of refraction becomes 90° and the light is no longer transmitted across the medium/medium interface. For angles greater in absolute value than the critical angle, all the light is reflected. This is called total internal reflection.

  6. At qc:

  7. Fresnel's equations describe the reflection and transmission of electromagnetic waves at an interface. That is, they give the reflection and transmission coefficients for waves parallel and perpendicular to the plane of incidence.

  8. Reflection coefficients:

  9. Transmission coefficients:

  10. external reflection internal reflection

  11. 2002 Q6 a) Write down Snell's law of refraction, explaining all the symbols you use. b) A narrow beam of light is incident from air at an angle of 45 degrees on a parallel-sided slab of glass, 1-cm thick, with refractive index 1.5. Calculate the angle of the beam inside the slab. c) Draw a diagram showing the passage of the light through the slab, showing clearly the angle you have just calculated, and hence find the lateral (perpendicular to the beam direction) shift of the emerging beam.

  12. 2003 Q4 a) State the law of refraction (Snell's law), and explain the terms in your equation with a diagram. b) Light from a source in air is incident on a block of quartz, at an angle of 40° to the normal. The light contains two wavelengths of 405 nm and 509 nm. The indices of refraction for quartz with respect to air at these wavelengths are 1.470 and 1.463 respectively. Calculate the angle between the two refracted rays in the quartz.

  13. 2005 Q11 A light bulb is set in the bottom of a 3.0-m-deep swimming pool. What is the diameter of the circle of light seen on the water's surface from above? [Note that nair = 1.00 and nwater = 1.33.]

  14. The speed of light in liquids is a. less than in air. b. greater than in air. c. the same as in air. d. zero, since particles can't move through solids. e. depends on the thickness of the liquid.

  15. A monochromatic (single frequency, single wavelength) light ray in air (n = 1) enters a glass prism (n = 1.5). In the glass prism a. both the frequency and the wavelength are the same as in air b. the frequency is the same, but the wavelength is greater than in air. c. the frequency is the same, but the wavelength is smaller than in air. d. the wavelength is the same, but the frequency is greater than in air. e. the wavelength is the same, but the frequency is smaller than in air.

  16. The speed of light changes when it goes from ethyl alcohol (n1 = 1.361) to carbon tetrachloride (n2 = 1.461). The ratio of the speeds v2/v1 is a. 1.99 b. 1.07 c. 0.93 d. 0.51 e. 0.76

  17. Light is refracted through a diamond. If the angle of incidence is 30, and the angle of refraction is 12, what is the index of refraction? a. 1.3 b. 2.4 c. 2.6 d. 1.8 e. 0.4

  18. A person in a boat sees a fish in the water (n = 1.33), the light rays making an angle of 40° relative to the water's surface. What is the true angle (in degrees) relative to the water's surface of the same rays when beneath the surface? a. 40 b. 35 c. 50 d. 55 e. 61

  19. A person looks horizontally at the edge of a swimming pool. If its length is 5 m, and the pool is filled to the surface, to what depth (in m) could the observer see? (n for water is 1.33) a. 3.2 b. 4.4 c. 2.1 d. 1.0 e. 0.3

  20. A layer of ethyl alcohol (n = 1.361) is on top of water (n = 1.333). At what angle relative to the normal to the interface of the two liquids is light totally reflected? a. 78 b. 88 c. 68 d. 49 e. the critical angle is undefined

  21. The laws of refraction and reflection are the same for sound as for light. The speed of sound in air is 340 m/s and in water it is 1510 m/s. If a sound wave approaches a plane water surface at an angle of incidence of 12, what is the angle of refraction?

  22. For a light ray that is partially reflected and partially refracted at a boundary between two media (the top one being air), as shown in the figure, for angles of incidence other than 0 the reflected ray is perpendicular to the refracted ray when

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