high school part 2 /2 by ssl technologies physics ex-51 click dispersion consider a beam of white...

High School

Part 2 /2

by SSL Technologies

Physics Ex-51

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DISPERSION

Consider a beam of white light (a mixture of all the colors) incidenton a prism. Each color refracts at a slightly greater angle uponentering the prism. When the colors emerge, again each refractsat a slightly greater angle. The net effect is that white light isseparated into its constituent colors. This process of the colorsspreading out is known as dispersion. The diagram belowillustrates this effect. The band of colors (identical to thecolors of a rainbow) is known as a spectrum.

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Dispersion

Physics Ex-51

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THE CRITICAL ANGLE

The critical angle of an optical (transparent) medium is the limitingangle of incidence that results in an angle of refraction equal to 90o.

Note : Given the index of refraction of an optical medium, we can use Snell’s Law to calculate the critical angle.

In using the formula, the angle of refraction is set to 90o.

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HISTORICAL NOTE

Rene Descartes was the first to publish the law of refraction in 1637.The reason the law is called Snell’s Law, however, is because ofjealousy on the part of the English and the Dutch who refused to

credit the discovery to someone from France.

Petty jealousy in science? Big time!

Physics Ex-51

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TOTAL INTERNAL REFLECTION

When a ray of light from within a medium strikes its surface at anangle greater than the critical angle, the refracted ray is reflectedback in the medium without emerging from that medium.

Study the illustration below.

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The critical angle is the angle ofincidence causing the refracted

ray to emerge at 90o to the normal(i.e. along the surface of the medium).

Physics Ex-51Question-1

Define total internal reflection and explain what is meant by thecritical angle.

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Total internal reflection refers to the bending of light as it travelsfrom one medium into another medium with the refracted raybending so much that it is reflected back into the same medium.

The critical angle is that angle which causes the refracted ray toemerge along the surface of the mediums. That is to say, therefracted ray does not emerge nor reflect back into its medium.


The index of refraction of a particular liquid is 1.60. A ray oflight inside the liquid strikes the liquid-air surface with anangle of incidence of 42o.

Determine whether the ray will exit into the air or be totallyreflected back into the liquid.

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In which medium does light travel faster, a medium with acritical angle of 25o or a medium with a critical angle of 30o

?Explain your answer.

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A ray of light enters crown glass from air with an angle of incidenceof 40o. Knowing that the angle of refraction is 25o, find the index ofrefraction of crown glass.

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The index of refraction of crown glass is 1.52.

Calculate its critical angle.

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A ray of light is incident upon an isosceles glass prism whoseindex of refraction is 1.50. As shown in the diagram below,the angle of incidence is 38o and the apex (top) angle of theprism is 50o. Calculate the angle of refraction.

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?41o


The diagram shows a beam of lighttraveling from water, through glass,

to air. If the angle of incidence ofthe water-glass surface is 30o,

calculate the angle of refractionfor the glass-air surface.

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As illustrated in the diagram below, a ray of light is incident uponthe surface of a medium at an angle of 60o at which point bothreflection and refraction occur. Knowing that the speed of lightis one and one-half times faster in air than in this medium, findthe angle formed by the refracted ray and the reflected ray.

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Sin


At what angle of incidence should a ray of light approach the surface of diamond (n = 2.42) from within the diamond so thatthe refracted ray emerges parallel to the surface.

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Critical angleof diamond.


A ray of light is incident at an angleof 40o upon the water in an aquarium.

As illustrated in the diagram on theright, the height of the water is 30 cm.

Find the lateral displacement of theray as it emerges the aquarium.

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B

D

C

A

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high school part 2 /2 by ssl technologies physics ex-51 click dispersion consider a beam of white...

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