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Prepared by: learnloophq@gmail.com
Chapter: 04. Light
Light Transmission through Materials: Transparent vs. Translucent vs. Opaque vs. Highly Polished Surfaces
Material Type
Definition / Description
Behavior of Light
Examples
Transparent Object
An object that lets most of the light pass through it
Reflects very little light
Thin clear sheet of glass
Translucent Object
An object that lets some light pass through it
Reflects some of the light falling on its surface
Thick sheet of glass, butter paper
Opaque Object
An object that does not let any light pass through it
Absorbs or reflects most of the light
Not mentioned in text
Black Opaque Object
A specific type of opaque object
Absorbs most of the light that falls on it
Not mentioned in text
Smooth / Polished Surface (Mirror)
A smooth and highly polished reflecting surface
Reflects most of the light falling on it
Mirror
Types of Mirrors: Plane Mirrors vs. Spherical Mirrors
Mirror Type
Surface Characteristics
Primary Uses
Image Characteristics
Plane Mirror
Flat, highly polished, and smooth
• Checking appearance• Makeup mirror / looking glass• Barber shops• Opposite walls of a room (to make it look spacious)• Laboratories• Solar cookers and solar geysers• Periscopes and kaleidoscopes
• Same size as the object• Laterally inverted• Image distance equals object distance from the mirror
Spherical Mirror
Not mentioned in text
Used by school bus drivers to see traffic coming from behind
Not mentioned in text
Rays of Reflection: Incident Ray vs. Reflected Ray
Ray Type
Definition
Direction of Travel
Notation (in Fig. 4.2)
Incident Ray
The ray of light which strikes the reflecting surface
Travels towards the reflecting surface
AO
Reflected Ray
The ray of light which is reflected back into the same medium after striking a surface
Travels away from the reflecting surface
OB
Angles of Reflection: Angle of Incidence vs. Angle of Reflection
Angle
Definition
Notation (in Fig. 4.2)
Relationship (Laws of Reflection)
Angle of Incidence
The angle between the incident ray and the normal
∠AON (or i)
Always equal to the angle of reflection
Angle of Reflection
The angle between the reflected ray and the normal
∠BON (or r)
Always equal to the angle of incidence
Types of Reflection: Specular (Regular) vs. Diffused (Irregular)
Feature
Specular (Regular) Reflection
Diffused (Irregular) Reflection
Reflecting Surface
Smooth surface (e.g., a mirror, wet road at night)
Rough, irregular surface (e.g., cardboard, paper, leaves)
Behavior of Reflected Rays
Reflected rays are parallel to one another
Incident parallel rays are reflected at different angles and in different directions
Visual Effect / Benefit
Causes a distracting glare for drivers on wet roads
Allows us to see the object from all angles
Adherence to Laws of Reflection
Obey the laws of reflection
Obey the laws of reflection (each individual ray follows the law)
Image Formation in a Plane Mirror: Point-Sized vs. Extended-Sized Objects
Object Type
Description
Ray Behavior
Image Characteristics
Point-Sized Object
A single point source of light (O)
Rays travel on all sides; two incident rays (OA, OC) reflect (AB, CD) and appear to meet at point I when extended backwards
• Image is a point (I) behind the mirror• Image distance equals object distance (OP = IP)
Extended-Sized Object
An object with physical height/dimensions (AB)
Multiple rays travel from extreme points (A, B), follow the laws of reflection, and appear to come from points A’ and B’
• Image (A’B’) is the same size as the object• Laterally inverted• Image distance equals object distance
Colours of Light: Primary Colours vs. Secondary Colours
Colour Category
Definition
Colors Included
How They are Formed / Obtained
Result of Mixing All
Primary Colours
Basic colours of light that cannot be obtained by mixing other colours, but produce other colours when mixed
Red, Green, Blue (RGB)
Found naturally; cannot be made by mixing other colours
Mix together to produce white light
Secondary Colours
Composite colours produced by mixing primary colours
Magenta, Cyan, Yellow
Created by mixing two primary colours:• Red + Blue = Magenta• Blue + Green = Cyan• Red + Green = Yellow
Not mentioned in text
Speed of Light in Different Mediums
Medium
Speed of Light
Relative Speed / Refractive Index Effect
Air or Vacuum
3 × 10⁸ m/s (approximately)
Maximum possible speed (fundamental constant c)
Water
2.25 × 10⁸ m/s
Slower than in air/vacuum, but faster than in glass
Glass
2 × 10⁸ m/s
Slower than in air/vacuum and water
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