lab2_Baidyrakhmankyzy_Zhansaya

Determination of the angle of total internal reflection at the boundary between two dielectric media

DONE BY: Baidyrakhmankyzy Zh.

CHECKED BY: Zvyaginceva O.A.

Almaty 2015

The purpose : To study the phenomenon of total internal reflection from the boundary of the optically less dense medium.

Introduction: Brief theoretical description

The incident and refracted rays, as well as perpendicular to the interface of two media, restoring to the point of incidence, lie in one plane. The ratio of the sine of the angle of incidence α to the sine of the angle of refraction β is the value constant for these two environments:

(1)

The constant value of n is a relative refractive index of the second medium relative to the first. The refractive index of the medium with respect to an vacuum is called the absolute refractive index.

The relative refractive index of the two media is the ratio of the absolute refractive index:

n = n2 / n1 (2)

The medium with the smaller absolute refractive index is called an optically less dense. When passing the light from the optically denser medium to an optically less dense n2 <n1 (e.g., glass to air) may be observed the phenomenon of total reflection, that is, disappearance of the deflected beam. This phenomenon is observed at angles of incidence greater than a certain critical angle αpr called the limiting angle of total internal reflection

For the angle of incidence α = αpr sin β = 1, the value of sin αpr = n2 / n1 <1.

If the second medium is air (n2 ≈ 1), the formula of which is written in the form

αpr sin = 1 / n, (3)

where n = n1> 1 - the absolute refractive index of the first medium.

Process of lab work:

1) The first thing that we have to do is to choose the number of lab work and the material. In my case this is a second lab work , with 1st material

2)Secondary, we have to replace the transporter in that way that we need. After we should move it and observe.

3)There you can see that until the degree is less or equal to 50 degree , we can see 3 red lines. Second red light is reflection, third one is refraction.

4) Then after we move the degree further than 50 degree, we can see that 3rd red line disappears

5)After we complete the table below.

№	angle of incidence 	Angle of refraction 	Average angle of incidence ср= (12)/2	marginal angle of total internal   reflections	Material, coefficient of refraction
1	0	0	25	α = αпр   50	Ice 1,3
2	50	96

6) In order to find the material we have to find the coefficient of refraction.

We have to find from this formula n : sin α_пр = 1 / n

We know that the angle of reflection is equal to angle of incidence. So we can write : n=1/ sin α_пр  => α = α_пр   ;n=1/sin50 = 1/0.76 = 1.3

We can check it : sinα/sinβ = n2/n1 sin50/sin96 = 1 /n1 0.76*n1=1;

n1=1.3

Conclusion:

When passing the light from the optically denser medium to an optically less dense n2 <n1, we can observe the phenomenon of total reflection. ie disappearing of the refraction. we can see it when the angle of incidence is bigger than a critical angle

Control questions :

1) The marginal angle of total internal reflection for the diamond is 24⁰. How will it change, if put the diamond in the water?

Material	Coefficient of refraction	The marginal angle
ice	1.3	50
Water	1.33	48.7
Glass	1.5	42
Diamond	2.4	24

sin α_пр = 1 / n

From the table and the formula we can see that the angle and coefficient of refraction are inversely proportional .So when we put the diamond to the water , the angle of refraction will decrase.

2) Does the energy loss in the optical fiber depend on its bending?

During the construction and operation of optical cable lines there might appear the operational losses. They are caused by a twist, and bend fibers deformation arising when applying coatings and in the manufacture of protective sheaths of the cable and during its gasket (Figure 2.4).

Microbending losses caused by the conversion of guided modes to radiation modes. They soar and become unacceptably large as the bending radius decreases to a critical value, which is typical for the OB is a few centimeters. Figure 2.4 shows how the variation of the boundary OB can result in higher-order modes of reflection angles at which the light transmittance further along OB becomes impossible. The light leaving the fiber. The development of production technology and OB FOC aimed at reducing these microscopic inhomogeneities.

3) How does a part of the energy emanating from a point source from an optically denser medium to an optically less dense depend on the refractive index, and why?

The energy is linear proportional with the velocity. From that we can make a decision:

1)sinα/sinβ=n2/n1=v1/v2;

n2/n1=v1/v2

n=1/v;

2)v^2 =w

v=(w)^1/2

3) n =1/(w)^1/2

w=1/n^2

The more is coefficient , the less is Energy. Inversely proportional

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