Reflection of Light

A Project Report

Prepared by: [Student Name]

Class 12, Physics

Under the Guidance of: [Teacher Name]

Certificate
This is to certify that the project report on “Reflection of Light” has been prepared by [Student Name], a student of
Class 12, under the guidance of [Teacher Name]. It is being submitted for the fulfillment of the course
requirements.
Acknowledgement
I express my sincere gratitude to my physics teacher and guide [Teacher Name] for their constant encouragement
and valuable guidance during this project. I also thank my parents and classmates for their support and
cooperation.
Index
1. Certificate
2. Acknowledgement
3. Introduction
4. Theory
4.1 Laws of Reflection
4.2 Types of Reflection
4.2.1 Specular (Regular) Reflection
4.2.2 Diffuse (Irregular) Reflection
4.2.3 Retro■reflection
4.3 Reflection from Plane Mirrors
4.4 Reflection from Spherical Mirrors
4.4.1 Concave Mirrors
4.4.2 Convex Mirrors
4.5 Mirror Formula and Magnification
5. Applications
6. Experiments
7. Conclusion
8. References
Introduction
Light is an electromagnetic wave, and when it encounters a boundary between two media, it can be reflected,
refracted, or absorbed. In this project, we focus on reflection, which is the phenomenon whereby light “bounces
back” from a surface. The fundamental laws governing reflection—namely, that the angle of incidence (θ■) equals
the angle of reflection (θ■), and that the incident ray, reflected ray, and the normal all lie in the same plane—apply
to every reflecting surface, whether perfectly smooth or rough. By studying reflection, we understand how images
form in mirrors, how everyday devices like periscopes and rear■view mirrors work, and how advanced
technologies such as solar concentrators and optical fibers exploit related concepts.
Theory
4.1 Laws of Reflection
1. Angle Equality: The angle of incidence (θ■) equals the angle of reflection (θ■). 2. Coplanarity: The incident ray,
the reflected ray, and the normal all lie in the same plane. These laws hold for any smooth reflecting surface
(plane or curved) and form the basis for all subsequent discussions on image formation and optical devices.

4.2 Types of Reflection

4.2.1 Specular (Regular) Reflection

Occurs when parallel incident rays strike a highly polished (optically smooth) surface, such as a glass mirror or a
calm water surface. All reflected rays remain parallel, preserving the original beam’s directionality. Produces clear,
well■defined images (virtual or real). Example: A plane glass mirror or a highly polished metal sheet.

4.2.2 Diffuse (Irregular) Reflection

Occurs when incident rays strike a rough surface, causing rays to scatter in many directions. Each microscopic
facet follows θ■ = θ■, but macroscopic scattering results in no clear image. Example: A painted wall, white paper,
or unpolished wood.

4.2.3 Retro■reflection
A special case in which scattered light is returned exactly back toward the source direction. Retro■reflective
surfaces use microstructures (corner■cube prisms or glass beads) so that each incident ray emerges parallel but
reversed. Examples: Road signs, bicycle reflectors, and certain animal eyes (tapetum lucidum in cats, deer).

4.3 Reflection from Plane Mirrors

Image Properties in a Plane Mirror: - Image is virtual (cannot be projected onto a screen) and erect (upright). -
Image distance behind mirror (v) equals object distance (u). - Image size equals object size (magnification = +1). -
Image is laterally inverted (left–right reversal). Ray Diagram: Incident ray from object point A reflects with θ■ = θ■;
extend reflected ray behind mirror to locate virtual image A'.
4.4 Reflection from Spherical Mirrors

4.4.1 Concave Mirrors

Focal Point (F): Half the radius of curvature (R), so f = R/2. Mirror Formula: 1/u + 1/v = 1/f. Image Cases: 1. Object
beyond C (u > R): Image is real, inverted, and diminished (between F and C). 2. Object at C (u = R): Image is real,
inverted, and same size (at C). 3. Object between C and F (R > u > f): Image is real, inverted, and magnified
(beyond C). 4. Object at F (u = f): Reflected rays are parallel; image at ∞. 5. Object between F and mirror (u < f):
Image is virtual, upright, and magnified behind mirror. Ray Diagram: Principal rays—parallel → reflect through F;
through F → reflect parallel; through C → reflect back.
4.4.2 Convex Mirrors
Focal Point (F) and Center (C): Behind the mirror (virtual); f = -R/2. Image Properties: Always virtual, erect, and
diminished (|m| < 1); image is located between F and mirror. Mirror Formula: 1/u + 1/v = 1/f (f < 0, v < 0). Ray
Diagram: Principal rays—parallel → reflect as if from F (behind); directed to F → reflect parallel; directed to C →
reflect back.
4.5 Mirror Formula and Magnification
Mirror Formula: 1/v + 1/u = 1/f → v = uf/(u - f). Sign Conventions: - Concave: u > 0, v > 0 (real image), f > 0. -
Convex: f < 0, v < 0 (virtual image). Linear Magnification: m = h'/h = -v/u. - m < 0: Inverted image; m > 0: Upright
image. - |m| < 1: Image smaller; |m| > 1: Image larger.
5. Applications
Reflection principles underpin a variety of optical instruments and everyday devices: 1. Plane-Mirror Applications:
- Periscope: Two plane mirrors at 45° allow viewing over obstacles (θ■ = θ■ at each mirror). 2. Concave-Mirror
Applications: - Solar Concentrators & Cookers: Parabolic dish focuses sunlight to focal point. - Headlights:
Concave reflector collimates lamp rays into parallel beams. - Reflecting Telescopes: Primary mirror gathers and
focuses distant starlight. 3. Convex-Mirror Applications: - Vehicle Rear-View/Side Mirrors: Provide wide field of
view, erect and reduced images. - Security Mirrors: Convex mirrors in stores offer a broad view of aisles. 4.
Retro-Reflectors & Safety: - Road Signs & Reflective Clothing: Glass beads or prisms send light back to source. -
Bicycle & Road Safety Equipment: Reflective tape and road markers. 5. Optical Fiber (Total Internal Reflection): -
Light is guided over long distances by repeated total internal reflection inside the fiber.
6. Experiments
6.1 Verification of the Laws of Reflection
Objective: Show that θ■ = θ■ and that incident and reflected rays lie in the same plane. Materials: - Ray box/laser
pointer - Plane mirror on stand - Drawing board with protractor, ruler, pencil Procedure: 1. Place plane mirror
vertically on board. 2. Draw normal at mirror's midpoint. 3. Shine beam at mirror at known θ■. 4. Mark incident and
reflected paths with pins or pencil. 5. Measure θ■ and θ■ using protractor; they should be equal. 6. Repeat for
various angles. Observation: θ■ ≈ θ■ consistently, confirming reflection laws; rays are coplanar.
6.2 Determination of Focal Length of a Concave Mirror
Objective: Find focal length f of a concave spherical mirror. Materials: - Concave mirror on stand - Candle or bright
lamp (object) - White screen (paper/card) - Meter scale Procedure: 1. Place mirror in dim room. 2. Position object
far (u ■ f). 3. Move screen along axis until sharp real image appears. 4. Measure mirror-to-screen distance = f. 5.
Alternatively, with finite u and v, use 1/v + 1/u = 1/f to compute f. Observation: If object at infinity, screen distance
≈ f. Finite method yields consistent f using mirror equation.
6.3 Demonstration of Total Internal Reflection (TIR)
Objective: Show TIR at an interface; relate to optical fibers. Materials: - Acrylic or glass block (water-filled or solid
acrylic) - Laser pointer - Protractor sheet - White paper Procedure: 1. Place block on white paper; outline block. 2.
Draw normal at intended beam entry point. 3. Shine laser inside block toward air boundary, starting with small
angle (< critical angle). 4. Increase angle; at critical angle (~48.6° for water-air), refracted beam skims boundary;
beyond, all light reflects internally (TIR). 5. For fiber optic demo, shine laser into acrylic rod; observe zig-zag
internal reflections. Observation: Below ~48°, partial refraction and reflection; at ~48°, refracted ray vanishes;
beyond, full internal reflection.
7. Conclusion
This project has: - Verified the laws of reflection (θ■ = θ■; rays coplanar). - Explored types of reflection: specular,
diffuse, retro-reflection. - Analyzed image formation in plane, concave, and convex mirrors, using ray diagrams
and mirror formulas. - Discussed applications: periscopes, rear-view mirrors, solar concentrators, telescopes, and
safety reflectors. - Performed experiments: verifying reflection laws, measuring concave mirror focal length, and
demonstrating TIR in fibers. The study shows how simple laws of reflection lead to diverse optical phenomena and
technologies, drawing from NCERT Class 12 Physics and HC Verma.
8. References
1. NCERT Class 12 Physics, Chapter “Ray Optics and Optical Instruments.” 2. HC Verma, Concepts of Physics,
Vol. 1, Chapter 24: “Reflection of Light.” 3. The Physics Classroom – “Reflection” tutorial. 4. Khan Academy –
“Reflection and Mirrors” videos. 5. Hecht, E. (2002). Optics (4th ed.). Addison-Wesley. 6. Serway, R. A., & Jewett,
J. W. (2013). Physics for Scientists and Engineers (9th ed.). Brooks/Cole.