ON

TOTAL INTERNAL REFLECTION

AND

SIMPLE ELECTRONIC BUZZER

Name:-

Class: - XII B Roll No.-AISSCE EXAMINATION – 2012-2013

Kendriya vidyalaya garden reach

Laboratory certificate

This is to certify that of Class XII B of Kendriya Vidyalaya Garden Reach has satisfactorily completed the project in physics for the AISSCE as prescribed by CBSE for the year 2012-13.

Date:-

Roll no:-

_______________ _______________ Signature of the internal examiner Signature of the external examiner

Acknowledgement

I thank my physics Sir , Mr S.N.Shama for his kind guidance and support. I would also like to thank my parents for encouraging me during this course of Physics Project.

- “Total internal reflection”- “Simple electronic buzzer”

Finally I would like to thank CBSE for giving me the opportunity to undertake this project.

_____________

Total internal reflection

Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to normal to the surface. If refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.

When light crosses a boundary between materials with different kind of refractive index, the light beam will partially refracted at the boundary surface, and partially reflected. However, if the angle of incidence is greater(i.e. the ray is closer to being parallel to the boundary) than the critical angle- the angle of reflection at which light is refracted such that it travels along the boundary- then the light will stop crossing the boundary altogether and instead being totally reflected back internally. This can only occur where light travels from a medium from higher refractive index to one with lower refractive index. For example, it will occur when passing from glass to air, but not when passing from air to glass.

Diamond total internal reflection

The brilliance of diamond is due to total internal reflection. Now m for diamond is 2.42o and c (the critical angle) is 24.4o for diamond-air interface. The faces of the diamond are so cut that a ray of light entering the diamond fall at angle greater than 24.4o. This results in multiple, total internal reflections at various angles and remains within the diamond. Hence diamond sparkles.

Optical description

Total internal reflection can be demonstrated using a semi-circular glass block. A “ray box” shines a narrow beam of light (a ”ray”) onto the glass. The semi-circular shape ensures that a ray pointing towards the centre of the flat face will hit the curved surface at a right angle. This will prevent refraction at the air/ glass boundary of the curved surface. At the glass/ air boundary of

the flat surface, what happens will depend upon angle. Where critical angle measurement is caused by the sun or a light source (measured normal to the surface).

- If incident is less than critical angle, the ray will split. Some of the ray will reflect off the boundary and some will refract as it passes through.

- If incident is greater than the critical angle, the entire ray will reflect from the boundary. This is called total internal reflection.

This physical property makes optical fibres useful and prismatic binoculars possible. It is also what gives diamonds their distinctive sparkle, as diamond has an unusually high refractive index.

Critical angle

The critical angle is the angle of incidence above which total internal reflection occurs the angle of incidence is measured with respect to the normal at the refractive

boundary. Consider a light ray passing from glass into air. The light emerging from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle (in air) reaches 90 degrees. It is at this point no light is transmitted into air. The critical angle -------- is given by snell’s law,

n1 sin--- = n2sin----

Rearranging Snell’s law , we get incidence

Sin---- = n2sin---/n1

To find the critical angle, we find the value for --.- when ---= 90o and thus sin--- = 1. The resulting value of— is equal to the critical angle ---- .

Now, we can solve for --- , and we get the equation for the critical angle.

---------------------

If the incident ray is precisely at the critical angle, the refracted ray is tangent to the boundary at the point of incidence. If for example, visible light were travelling through acrylic glass (with an index of refraction 1.50) into air (with an index of refraction of 1.00), the calculation would give the critical angle for acrylic into air, which is

-----------------

Light incident on the border with an angle less than 41.8o would be partially transmitted, while light incident on the border at larger angle with respect to normal would be totally internally reflected.

If the fraction n2/n1 is greater than 1, then arcsine is not defined- meaning that total internal reflection does not occur even at very shallow or grazingincident angles.

So the critical angle is only defined when n2/n1 is less than 1.

Demonstration- 1.

Object: - To demonstrate the phenomenon of the total internal reflection.

Apparatus:- A cylindrical glass trough, water in a jug, a circular plastic disc which can float in water, an illuminating torch bulb which can be placed at the bottom Centre of trough.

Theory:- When light travels from a denser to a rarer medium and the incident in denser medium at an angle more than critical angle C, then it is totally internally reflected.

For height H and circle radius R,

tanC= R/H or R=H. tanC , no light will go out.

For a greater height light will be received outside the water.

Procedure:-

- Put empty glass trough on a table.- Fit an illuminated tiny torch bulb at the centre of the

through. Bulb illumination will be seen.- Pour some water in the trough and float the circular

plastic plate in it, keeping it’s centre in vertical line with trough centre. Illuminated water surface will be visible.

- Pour some water in the trough and float the circular plastic plate in it, keeping its centre in vertical line with trough centre. Illuminated water surface will be visible.

- Pour slowly more and more water. Area of illuminated water surface will go on decreasing.

- Go on pouring till no illuminated water surface is visible

Here R/H = tanCFor water, C= 48.6o and tan1.3428

Observation:- Illuminated water surface totally disappear when H= R/tanC i.e., R=H tanC.

Result:-

- Whenever a light travels from a denser medium to a rarer medium at an angle is equal to critical angle, the light is perpendicularly refracted.

- If light is incident at an angle greater than the critical angle, the light is reflected back in the denser medium. This phenomenon is known as “Total internal reflection”

DIAGRAM:

Simple electronic buzzer

Demonstration-2.Object:- To demonstrate the working principle of a simple electronic buzzer.Apparatus:-

- Diode (By 125 or 127)- n-p-n transistor (AC 127 or AC 128)- Transformer - Speaker (5Ω to 8-Ω)- Variable resistors (1kΩ)- Battery (3V)- Push button

Circuit diagram:-

Procedure:-

- Make the arrangement as shown in fig. 1. The transistor acts as high frequency oscillator in common-emitter configuration. The primary

aim of the transformer couples the emitter-base (input) circuit with emitter-collector (output) circuit

- It works as the push button P is pressed.

Observations:-When the push button P is closed the transistor junction becomes biased and it works as a oscillator. High frequency A.C. passing through transformer primary operates its secondary to feed the speaker coil. A thrill sound is produced.1kΩ variable resistor changes the tone of the sound produced.

Result:-The arrangement is very much useful

- It can be used as an ideal cycle horn.- It can also be used as a car bell.

Bibliography

- Ncertbooks.prashanthellina.com/12_physics.html

- Nageen CBSE Physics for class XII by Kumar Mittal

- Daswani Physics CBSE for class XII- ICBSE.wordpress.com/category/class-xii-

physics-project- Askphysics.com/download-newly-included-

portion-cbse-class-12-phy- www.ischools.in/physics/

CBSE_Physics_Projects_Class_12.php- http://plustwophysics.com/investigatory-

project-reintroduced-in-CBSE-physics-curriculum.

- Physics.2lv.in- www.allprojectreports.com/CBSE...Projects/

Physicsprojectreport.htm

thank you ………..