# Luz y ondas

Páginas: 6 (1384 palabras) Publicado: 1 de noviembre de 2011

GROUP A
1. What is a lumen? Is it more like a watt or a joule? How does the lumen differ from the watt?
Rta. Lumen (lm), is the unity of the international measurement system to measure the luminous flux, a measure of perceived light output; The difference between watts and lumbers is that the watt measures potency and the lumen only measures the light, so if we have heat and light of a bulb we can measure in watts. its more like a watt because de joule it’s a measure of work, a watt measures the energy, so, light its related to heat, there´s energy, so then you can measure with watts.
2. How is the modern standard light source superior to the ordinary candle as a standard?
Rta. The candle has an uncontrolled combustion for that reasonits better; making it a really fast changing standard measure, so, the measure would be inexact using a candle
3. What is a unit solid angle?
Rta. Is the spatial angle comprises an object seen from a given point, which corresponds to the area of space bounded by a conical surface. Measured the apparent size of the object. The unit solid angle is steradian (Sr); is the area of a sphere
4.Distinguish between the lumen and the candle.
Rta. The difference is that the lumen measures the luminous flux and the candle measures the luminous intensity.
5. The absolute efficiency of an incandescent lamp as a source of light is about 2 per cent. What happens to the 98 per cent of power that is wasted?
Rta. The 98 % of the power is transformed into heat
6. Explain why theillumination at a surface is inversely proportional to the square of the distance from a point source of light.
Rta. the illuminated object is from the source of light, the less the light over the object will be.
7. Give to examples not mentioned in the text of (a) specular reflection, (b) diffuse reflection.
Rta. A. imaging using a planer mirror. In specular reflection, the angle of incidenceof light rays equals the angle of reflection at each point on the normal N.
b. an example of diffuse reflection is when the light reflects off my shirt, knowing that my shirt´s surface isn’t flat.
8. (a) write a statement telling how the angle of reflection changes as the angle of incidence changes. (b) how does the angle between the incident and the reflected rays change as the angle ofincidence changes?
Rta. A. when the incidence angle gets bigger 9 degrees, the reflected ray angle gets bigger 9 degrees. When the incidence angle gets smaller 9 degrees, the reflection angle gets smaller 9 degrees; everything has a relation.
b. the angle between the two beams is sometimes smaller than the angle of incidence. This happens when the angle of incidence is bigger
9. Explain whythe path of a light ray bends as it passes from water into air.
Rta. Wave`s velocity changes when the wave changes from one material to another(refraction), so it changes its direction.
10. Define index of refraction.
Rta. index of refraction is a measure that determines the reduction of the speed of light as it propagates trough a homogeneous medium; refractive index is the phase change forunit length, is the wave number in the middle (k) is n time larger the wave number in vacuum (k0).
11. Explain why white light may be separated into its component colors when it passes through a prism.
Rta. The angle of diffraction depends of two things: the difference in the diffraction index between the two mediums, and the wavelength. The diffraction angle is proportionate to thewavelength, meaning that the longer the wavelength of the light, the greater angle the light bends as it crosses the medium boundary .Since red light has a longer wavelength than blue light does, red light diffracts, or bends, at a greater angle than blue light bends when they both strike the prism at the same angle of incidence. White light contains all the colors of the rainbow. So when white light...

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