General Physics Reviewer: Electromagnetic Spectrum and Optics

THE ELECTROMAGNETIC SPECTRUM

• Definition of Electromagnetic Spectrum: A continuum of all electromagnetic waves arranged according to frequency and wavelength.
• Radiowaves:     * Primary Uses: Used for broadcasting and communications.     * Wavelength Range: > 1\,\text{m}.     * Frequency Range: < 3 \times 10^8.     * Energy Level: Characterized by having the lowest energy and lowest frequency.     * Wavelength Characteristic: Characterized by having the longest wavelength.
• Microwaves:     * Primary Uses: Used for radar, satellite communication, and cooking.     * Wavelength Range: $1\,\text{m} - 1\,\text{mm}$.     * Frequency Range: $3 \times 10^8\,\text{Hz} - 3 \times 10^{11}\,\text{Hz}$.     * Examples: Wifi, microwave oven, and radar systems.
• Infrared (IFRARED):     * General Properties: Felt as heat.     * Primary Uses: Used in thermal imaging and remote controls.     * Wavelength Range: $1\,\text{mm} - 700\,\text{nm}$.     * Frequency Range: $3 \times 10611\,\text{Hz} - 4 \times 10^{14}\,\text{Hz}$.
• Lightwaves:     * Definition: The narrow band of wavelength detectable by the human eye.     * Wavelength Range: $700\,\text{nm} - 400\,\text{nm}$.     * Frequency Range: $4 \times 10^{14}\,\text{Hz} - \&amp;.5 \times 10^{14}\,\text{Hz}$.
• Ultraviolet (UV) Rays:     * Primary Uses: Used in sterilization and causing flourescence.     * Wavelength Range: $400\,\text{nm} - 10\,\text{nm}$.     * Frequency Range: $7.5 \times 10^{14}\,\text{Hz} - 3 \times 10^{16}\,\text{Hz}$.     * Source: Known as high-energy rays originating from the sun.
• X-Rays:     * Definition: High-energy radiation used in medical imaging to view dense materials like bones.     * Discovery: Discovered by Wilhem Conrad Rontgen in 1895.     * Wavelength Range: $10\,\text{nm} - 0.01\,\text{nm}$.     * Frequency Range: $3 \times 10^{16}\,\text{Hz} - 3 \times 10^{19}\,\text{Hz}$.
• Gamma Rays:     * Sources and Uses: Emitted by radioative materials and used for cancer treatment.     * Wavelength Range: $< 0.01\,\text{nm}$.     * Frequency Range: $> 3 \times 10^{19}\,\text{Hz}$.     * Energy Level: Characterized by having the highest energy and highest frequency.

INTRODUCTION TO WAVES

• Waves (General Definition): Waves are disturbances that carry energy from one place to another (Russel, 2015).
• Mechanical Waves:     * Definition: These waves require a medium (particles) to travel through.     * Examples: Sound waves and water waves.
• Electromagnetic Waves:     * Definition: These waves do not require a medium to gravel through and can travel through a vacuum.     * Examples: Visible light, Radio waves, and Gamma Rays.
• Parts of a Wave:     * Crest: Otherwise known as the peak; the highest point of a wave.     * Rest or Equilibrium Position: The undisturbed position of the particles if they do not vibrate.     * Trough: The lowest point of a wave.     * Amplitude ($A$): The maximum disturbance from the crest of the wave from its rest position.         * It represents the wave’s height.         * The unit for Amplitude is metres ($m$).     * Wavelength ($\lambda$): A set distance that represents the full cycle of a wave.         * It can be measured from crest to crest, from trough to trough, or between any two consecutive points in the wave cycle.         * The unit for wavelength (Greek letter lambda) is metres ($m$).     * Frequency: The number of waves passing a specific point per second.         * The unit of Frequency is hertz ($Hz$).         * $1\,\text{Hz} = 1\,\text{cycle per second (1/s)}$.     * Velocity of a Wave:         * Wave speed or velocity is the distance a wave travels per second.         * It is also the rate at which energy is transferred through a medium.         * The unit for wave velocity is metres per second ($m/s$).

PROPERTIES OF LIGHT AND INTERACTION WITH MATTER

• Light (General Properties):     * A form of energy that causes the sensation of vision.     * Travels from a straight line.     * The speed of light is faster than sound.
• Reflection of Light: The process through which light rays fall on the surface and get bounced back.
• Classification of Materials Based on Light Transmission:     * Transparent: Allows almost all light to pass through, making objects on the other side clearly visible. Examples include clear glass, water, air, and clear plastic.     * Translucent: Allows some light to pass through but diffuses (scatters) it, making objects on the other side blurry or indistinguishable. Examples include frosted glass, wax paper, butter paper, sunglasses, and frosted light bulbs.     * Opaque: Does not allow light to pass through; it blocks light entirely, creating a sharp shadow. Examples include wood, stone, metals, thick books, and bricks.

PRINCIPLES AND ELEMENTS OF REFLECTION

• Types of Reflection:     * Regular Reflection (Specular): Occurs on very smooth, polished surfaces where all light rays bounce off at the same time.     * Diffuse Reflection: Occurs on rough or uneven surfaces.
• Law of Reflection: A rule describing how light (or any wave) bounces off a surface; when a light ray hits a surface, it reflects at the exact same angle at which it arrived.
• The Two RU;ES of Reflection:     1. Angle Law: The angle of incidence (incoming light) is always equal to the angle of reflection (outgoing light).     2. Coplanarity Law: The incoming ray, the reflected ray, and the ‘normal’ (an imaginary line perpendicular to the surface) all lie on the same flat plane.
• Elements of Reflection:     * Angle of Incidence: The angle formed by a ray incident on a surface and a line perpendicular to the surface at the point of incidence.     * Angle of Reflection: The angle formed by a reflected ray and a line perpendicular to the surface at the point of reflection.     * Incident Ray (Incoming Light): The light beam traveling toward the surface.     * Reflected Ray (Bouncing Light): The light beam that bounces away from the surface.     * Normal (‘Reference Line’ The Imaginary $90$ Degree): An imaginary line drawn at an angle to the surface at the point where the light hits. All angles are measured from this line, not the surface itself.
• Refraction: The bending of light when it passes from one clear material into another, occurring because light changes speed.
• Snell’s Law: The formula used to calculate exactly how much the light will bend.

GEOMETRIC OPTICS: MIRRORS AND LENSES

• Plane Mirrors: A flat, smooth reflective surface that forms images by reflecting light.     * IMAGE CHARACTERICTICS:         * Location: Position of the image formed.         * Orientation: Arrangement of the image formed (Upright/erect, Inverted, or laterally inverted).         * Size: Describes how big the image is compared to the object (Same size, enlarged, or reduced).         * Type of Image:             * Virtual: Image you can see but cannot catch on a screen.             * Real: Image you can project onto a screen.
• Curved Mirrors: A curved mirror formed by a part of a hollow glass sphere with a reflecting surface.     * Concave Mirror: A curved mirror with the reflecting surface on the hollow side.     * Convex Mirror: A curved mirror with the reflecting surface on the outer side.
• Lenses: An optical device used to refract light and form images.     * Convex Lens: Thicker at the center and converge light to a point.     * Concave Lens: Thinner at the center and diverge light; always form smaller, upright, virtual images.

THE HUMAN EYE AND VISION

• Human Eye (Definition): An organ in the human body that controls sight and allows a person to see.
• Anatomical Parts and Functions:     * Conjunctiva: Membrane covering the eyelids and the surface of the eye. Function: protects the eye and keeps it wet.     * Cornea: Transparent outer layer at the front of the eye. Function: Helps the eye focus on light.     * Iris: Visible, coloured part of the eye. Function: Controls the amount of light that enters the eye.     * Pupil: Black circular area in the middle of the iris. Function: Responsible for the volume of light that enters the eye.         * Mydriasis: The dilation or widening of the pupil.         * Miosis: The constriction or narrowing of the pupil.     * Lens: Transparent structure. Function: Bend light rays that enter the eye.     * Accommodation: Ability of the eye to adjust its focal length (lens) to bring the image of far and near objects into focus on the retina.     * Vitreous Body: Gel substance found throughout the eye. Function: Keeps the eye in its round shape and maintains eye pressure.     * Retina: A layer of tissue located directly at the back of the eye. Function: To receive light that comes in through the eye's lens and translate that light into images.     * Optic Nerve: Function: Controls and transmits all visual information to the brain.     * Sclera: Visible whites of the eye. Function: Shields the eye from injury and helps keep its shape.
• Vision Defects and Corrective Lenses:     * Myopia (Nearsightedness): Inability of the eye to focus on distant objects. Corrective lens: Diverging or concave lens.     * Hyperopia (Farsightedness): Inability of the eye to focus on nearby objects. Corrective lens: Converging or convex lens.     * Presbyopia: The condition where individuals lose the ability to see near objects clearly as they get older.     * Astigmatism: A vision condition where a person sees blurry or distorted images at all distances. Corrected by a Cylindrical Lens.