Demonstration of the Phenomenon of Total Internal Reflection
Name: ___________
Class/Section: ___________
Roll Number: ___________
Teacher: ___________
School: ___________
Academic Year: ___________
Aim: To demonstrate the phenomenon of Total Internal Reflection.
Introduction: Total Internal Reflection (TIR) occurs when light travels from a
denser to a rarer medium and the angle of incidence exceeds the critical angle,
resulting in the light being completely reflected back into the denser medium.
Theory:
- Refraction: Bending of light as it passes from one medium to another.
- Snell's Law: n1*sin(i) = n2*sin(r)
- Critical Angle: Angle of incidence in denser medium for which refraction angle =
90°.
- Condition for TIR: i > critical angle.
Diagram: [Draw semi-circular prism with incident, refracted, and reflected rays]
Materials Required:
- Semi-circular glass prism
- Laser pointer / ray box
- White sheet of paper
- Pencil
- Protractor
- Mirror (optional)
Experimental Setup:
Place the semi-circular prism on white paper. Direct a laser beam along one edge.
Mark the path of incident, refracted, and reflected rays.
Diagram: [Draw setup showing prism, light source, rays, and angles]
Procedure:
1. Place the prism on a white sheet.
2. Direct a narrow light ray from the laser along the prism edge.
3. Mark incident, refracted, and reflected rays.
4. Increase the angle of incidence gradually.
5. Observe the angle where the light is completely reflected inside (TIR occurs).
6. Measure the angles using a protractor.
Observations:
Angle of Incidence (i)
Refraction Observed
Reflection Observed
TIR (Yes/No)
20°
Yes
No
No
40°
Yes
Partial
No
Critical Angle ~42°
Along boundary
Yes
Partial
50°
No
Yes
Yes
Graph / Figure (Optional):
Plot of Light Intensity vs Angle of Incidence.
Diagram: [Draw optical fiber or graph showing TIR]
Applications:
1. Optical fibers in communication and medical endoscopy.
2. Diamonds sparkle due to TIR.
3. Prisms in binoculars and periscopes.
4. Mirages in deserts.
Precautions:
- Avoid direct eye exposure to laser.
- Handle prism carefully to prevent breakage.
- Use a proper protractor for measurement.
Conclusion:
Total Internal Reflection occurs when light passes from a denser to a rarer medium
and the angle of incidence exceeds the critical angle. It is used in optical fibers,
binoculars, and diamonds.
Bibliography:
1. NCERT Class 12 Physics Textbook.
2. Halliday, Resnick & Walker, Fundamentals of Physics.
3. Online references: Educational Physics websites.