Introduction to Light and Its Sources

Introduction to Light

• Light travels extremely fast, filling a dark room immediately when a light switch is turned.
• Light travels so quickly it could circle Earth's equator 7.5 times in one second.
• Light travels in a straight line.

Production of Light

• Two kinds of light sources:
• Luminous sources produce their own light (e.g., flashlight, flame).
• Non-luminous sources do not produce light but can be seen when reflected light hits them (e.g., textbook, chalkboard).

Different Light Sources

Light as an Electromagnetic Wave

• Light energy travels through radiation.
• Light shows wave-like properties under certain conditions.
• Light travels as a particle called a photon.
• Lasers show different colours reacting differently to various materials.

Basic Light Properties

• Light is always a particle but can travel as a wave or a straight line.
• As a particle, light plays a role in interactions like the photoelectric effect and scattering.
• As a wave, it travels through media like air and water.
• Light travels in a straight line in uniform media or free space without obstructions.
• Light is a transverse wave with alternating electric and magnetic fields.
• Light waves do not need a medium to travel.
• Trough is the bottom of a wave, crest is the top of the wave, and amplitude is the measure of the middle point of elevation.
• Electromagnetic spectrum classifies electromagnetic waves, with visible light among them.

Colours Associated with Visible Light

• White visible light is composed of a continuous spectrum of colours seen by the human eye (rainbow).
• Each colour is associated with a specific wavelength and frequency.
• Wavelengths range from 400 to 700 nm.
• A prism can separate sunlight or white light into the colours of a rainbow.

Laws of Reflection

• The angle of incidence equals the angle of reflection.
• The incident ray, reflected ray, and the normal lie in the same plane.

Properties of Plane Mirrors

• Objects can reflect or absorb colours.
• Objects appear black when all colours are absorbed and none are reflected; white if all colours are reflected.
• Mirrors reflect all light and absorb none.
• The front of a mirror is usually glass; the back is a reflective layer (usually aluminum or silver).
• Terms like image, reflection, incident ray, reflected ray, and normal are important concepts related to mirrors.

Ray Diagrams

• Ray diagrams are theoretical tools demonstrating light pathways from one point to another, showing interactions with objects.
• These diagrams visually depict the reflection of light from a surface.
• Different types of ray diagrams are used for various scenarios, such as those involving straight angles and different angles.

Characteristics of an Image

• Image size can be the same size as the object, larger, or smaller.
• Image attitude can be upright or inverted.
• Image location is determined by its position relative to the object, either closer than, farther than, or the same distance as the object.

Concave and Convex Mirrors

• Concave mirrors curve inward.
• Convex mirrors curve outward.
• How objects appear in each type of mirror depends on the object's distance from the mirror:
  • Concave mirrors can produce larger, upright images of close objects and smaller, inverted images of distant objects.
  • Convex mirrors always produce smaller, upright, and virtual images, regardless of the object's distance.

Lens Types

• Converging lenses, also called convex lenses, are thicker in the middle and thinner at the edges.
• Diverging lenses, also called concave lenses, are thinner in the middle and thicker at the edges.

Types of Lens Images

• Converging lenses can form real or virtual images, depending on the object's location.
• Diverging lenses only create virtual images.

Thin Lens Equation

• 1/do + 1/di = 1/f.
• The equation describes the relationship between the object's distance (do), the image's distance (di), and the focal length (f).
• Positive values are used for real images/objects, while negative values are used for virtual images/objects.
• The focal length (f) is considered positive for converging lenses and negative for diverging lenses.

Magnification Equation

• M = hi/ho = −di/do.
• Magnification, M, describes the image's size relative to the object's size.
• Positive magnification means the image is upright; negative, inverted.

Refraction

• Refraction is the change in the direction of light when it passes from one medium to another.
• The speed of light varies depending on the medium it travels through.
• Light bends toward the normal when it slows down in the second medium and bends away from the normal when faster.

Index of Refraction

• The refractive index is the ratio of the speed of light in a vacuum to the speed of light in a given medium.
• Different materials have different indices of refraction.

Human Eye

• The eye uses a converging lens (cornea and lens) system to focus light on the retina.
• The iris controls the amount of light that enters the eye.
• The cornea is the transparent outermost layer that aids in focusing.
• The pupil is the opening in the iris, through which light passes.
• The lens focuses light onto the retina, where it is converted into signals that are sent to the brain.
• Differences in vision (nearsightedness, farsightedness, astigmatism) are caused by issues with the shape or clarity of the cornea/lens and can be corrected with lenses.

Photoreceptors

• Light-sensitive cells called photoreceptors (rods and cones) convert light into electrical signals.
• Rods detect shades of gray and are responsible for vision in low-light conditions.
• Cones detect colour and are responsible for vision in bright-light conditions.

Other Information

• Electromagnetic spectrum: covers all types of electromagnetic waves from radio waves to gamma rays.
• Different types of electromagnetic waves have different wavelengths and frequencies.