reflectvion, refractin, and prism

1. Reflection of Light

Definition

Reflection occurs when light strikes a surface and bounces back into the original medium.

Key Facts

  • Reflected light travels at the same speed as the incident light.

  • Wavelength remains unchanged.

  • Amplitude may change.

  • Most visible objects are seen because they reflect light.

Important Terms

  • Incident Ray: Incoming light ray.

  • Reflected Ray: Light ray that bounces off the surface.

  • Normal: Imaginary line perpendicular to the surface.

Law of Reflection

The angle of incidence equals the angle of reflection.

θi=θr\theta_i = \theta_rθi​=θr​

Where:

  • θᵢ = angle of incidence

  • θᵣ = angle of reflection

Special Cases

  • 0° incidence: Reflected ray retraces the same path.

  • 90° incidence: Ray travels along the surface.

2. Ray Model of Light

Definition

The ray model describes light as traveling in straight lines called rays.

Characteristics

  • Light travels in straight paths until it encounters a boundary or obstacle.

  • Explains shadows, mirrors, and many everyday optical phenomena.

Evidence

  • Sunlight through a doorway forms straight beams.

  • Dust particles can reveal light's linear path.

3. Types of Reflection

A. Specular Reflection

Definition

Reflection from a smooth, shiny surface.

Characteristics

  • Reflected rays remain parallel.

  • Produces clear images.

Examples

  • Mirrors

  • Calm water

  • Polished metal

B. Diffuse Reflection

Definition

Reflection from a rough surface.

Characteristics

  • Each ray still obeys the law of reflection.

  • Different surface normals cause rays to scatter.

  • No clear image forms.

Examples

  • Walls

  • Paper

  • Wood

4. Applications of Reflection

Periscope

Purpose

Allows viewing over obstacles or above water.

Structure

  • Two mirrors

  • Each mirror at 45°

  • Mirrors parallel to each other

Uses

  • Submarines

  • Observation devices

Solar Cooker/Oven

Principle

Uses mirrors to concentrate sunlight.

Result

  • Concentrated solar energy heats food.

  • Can cook or sterilize food.

5. Refraction of Light

Definition

Refraction is the bending of light when it passes from one medium to another.

Cause

Refraction occurs because light changes speed in different media.

Important Rule

No bending occurs if light enters along the normal (0° incidence).

Refraction Behavior

Entering a Slower Medium

Examples:

  • Air → Water

  • Air → Glass

Result:

  • Light slows down.

  • Light bends toward the normal.

Entering a Faster Medium

Examples:

  • Water → Air

  • Glass → Air

Result:

  • Light speeds up.

  • Light bends away from the normal.

6. Optical Illusions Caused by Refraction

Bent Stick in Water

Why It Happens

  • Light bends when moving between water and air.

  • The brain assumes light travels in straight lines.

  • The submerged portion appears displaced.

Result

The stick appears bent at the water surface.

Apparent Position vs Actual Position

Objects underwater appear:

  • Closer to the surface

  • Higher than their true position

Example:

  • Fish seen from above water.

7. Mirage

Definition

A visual illusion often seen on hot roads.

Cause

Different air temperatures create layers with different refractive indices.

Process

  1. Air near road is hotter.

  2. Hot air is less dense.

  3. Light bends through layers of air.

  4. Sky appears reflected on the road.

Appearance

Looks like water on the road.

8. Prisms

Definition

A prism is a transparent solid with flat polished surfaces that refracts light.

Common Material

  • Glass

Shape

Often triangular in physics laboratories.

Functions

  • Refract light

  • Separate white light into colors

  • Reflect light in optical devices

9. Dispersion

Definition

The separation of white light into its component colors.

Cause

Different colors travel at different speeds in a medium.

Important Fact

Violet light:

  • Higher frequency

  • Slows down more

  • Bends more

Red light:

  • Lower frequency

  • Slows down less

  • Bends less

Color Order

From least bent to most bent:

Red → Orange → Yellow → Green → Blue → Indigo → Violet

10. Speed of Light

In a vacuum:

c=3.0×108 m/sc = 3.0 \times 10^8\ \text{m/s}c=3.0×108 m/s

Where:

  • c = speed of light in vacuum

11. Rainbow Formation

Steps

  1. Sunlight enters a water droplet.

  2. Light refracts and disperses.

  3. Light reflects inside the droplet.

  4. Light refracts again as it leaves.

  5. Colors spread out and reach the observer.

Important Facts

  • Your back is always toward the Sun when viewing a rainbow.

  • Each droplet produces all colors, but you see only one color from each droplet.

Rainbow Color Arrangement

  • Outer edge: Red

  • Inner edge: Violet

Quick Review

Reflection

  • Light bounces off a surface.

  • Angle of incidence = Angle of reflection.

Refraction

  • Light bends when entering a different medium.

  • Caused by change in speed.

Specular Reflection

  • Smooth surface.

  • Clear image.

Diffuse Reflection

  • Rough surface.

  • No clear image.

Dispersion

  • White light separates into colors.

Prism

  • Refracts and disperses light.

Rainbow

  • Produced by refraction, reflection, and dispersion in water droplets.