Reflection of Light and Plane Mirrors

Reflection of Light

• Reflection is the behavior of light bouncing off a surface so that images can be seen.
• The Law of Reflection applies to any smooth surface, including mirrors.
• This law states that the angle of incidence equals the angle of reflection when light strikes a surface.
• Specular reflection occurs when a smooth surface bounces light in one direction, creating a clear reflection.
• Diffuse reflection occurs when a rough surface reflects light in various directions, resulting in a hazy image.
• Smooth surfaces filled with rainwater cause glare at night due to the concentrated specular reflection of headlights.
• Photography utilizes both specular and diffuse reflection to capture images of subjects.

Plane Mirrors

• Plane mirrors produce virtual images.
• The images are erect and the same size as the object.
• The object's distance from the mirror equals the image's distance.
• Images are laterally inverted

Real vs Virtual Images

• Real images are formed when light rays converge after reflection.
• Virtual images are formed when light rays only appear to converge when traced backward.

Types of Mirrors

• There are two kinds of mirrors
• Plane mirrors
• Spherical Mirrors
• Convex mirrors bulge outward and show things upright but smaller.
• Concave mirrors are hallowed inwards.
• Concave mirror image characteristics are dependent on object position relative to the focal point and center of curvature.
• Real, inverted images form when the object is beyond the center of curvature.
• Virtual, upright, magnified images form when the object is between the focal point and the center of curvature.
• Concave mirrors magnify images for makeup, shaving, and dental work.
• Telescopes contain concave mirrors.
• Convex mirrors always produce virtual, upright, and diminished images that appear located behind the mirror.
• Convex mirrors provide a wide range of view and are used for security and in car side-view mirrors.

About Light

• Light is a form of energy that helps us see
• Sunlight, light bulbs, and flashlights are all sources of light.
• Light travels in a straight line called a "ray."

Light Spectrum

• Electromagnetic radiation is a form of energy that travels in waves through space
• Visible light is the part of electromagnetic radiation humans can see.
• Visible light consists of different colors, each with distinct wavelengths and energy.
• The colors of visible light, ordered from lowest to highest energy, are: Red, Orange, Yellow, Green, Blue, Indigo, and Violet.
• Shorter wavelengths have higher energy, while longer wavelengths have lower energy.
• The visible spectrum ranges from violet to red, with energy increasing from red to violet.

Light Wavelengths

• Wavelengths are measured in meters (m) and nanometers (nm).
• A nanometer is one-billionth of a meter.
• Red has the longest wavelength, between 625 and 740 nm.
• Violet has the shortest wavelength, between 380 and 440 nm.
• The wave with the greatest frequency has the shortest wavelength.
• Violet light has the shortest wavelength, highest frequency, and highest energy within the visible spectrum.
• Red light has the longest wavelength, lowest frequency, and lowest energy within the visible spectrum.

Dark Rooms

• Dark rooms exclude normal light.
• Dark rooms are used for processing light-sensitive photographic materials.
• Red light is used in photographic darkrooms because its longer wavelength is less likely to affect photosensitive materials.

Why Sunburn

• Ultraviolet (UV) light is a higher energy form of electromagnetic radiation compared to visible light.
• Ultraviolet (UV) rays penetrate the skin and damage DNA in skin cells.
• Visible light has lower energy and longer wavelengths compared to UV light.

Color

• Color is the perception of different light wavelengths, making objects look different.
• When light strikes an object, some is absorbed and some is reflected back.
• The colors we see are the result of the reflected light.
• If an object reflects green wavelengths, it is perceived as green.
• Black objects absorb all wavelengths.
• White objects reflect all wavelengths.
• The colors objects appear to be is dependent on the object’s natural vibrating frequencies.
• A green object reflects green light and absorbs all other colors.

Dispersion

• Dispersion separates visible light into its component colors.

Refraction of Light

• Refraction occurs when light bends as it passes from one medium to another because the speed of light is slower in water
• Refraction explains optical illusions like mirages and rainbows, and halos around the sun or moon.
• Snell's Law, or the law of refraction, relates to the density of a medium.
• Density refers to how closely packed the particles are in a substance.
• The refractive index measures how much light speed reduces in a medium compared to its speed in a vacuum.
• Light slows down and bends towards the normal when it travels from a less dense to a denser medium (positive refraction).
• Light speeds up and bends away from the normal when it travels from a denser to a less dense medium (negative refraction).
• A mirage is a natural optical illusion caused by refraction.
• Atmospheric refraction occurs on hot sunny days, creating a temperature gradient and varying optical density, resulting in mirages.
• Rainbows form when light refracts as it enters raindrops, dispersing into a spectrum of colors through total internal reflection.
• Light disperses into an array of colors that we see as a rainbow while exiting water-air interface.
• Secondary rainbows result from light undergoing two internal reflections and refractions within a raindrop.
• Higher and fainter than the primary rainbow, secondary rainbows have the color sequence reversed.

Scattering of Light

• Scattering happens when light interacts with particles smaller than its wavelength, changing its direction and spreading it out.

Rayleigh Scattering

• Rayleigh Scattering is an optical phenomenon is dependent on the size of particles
• The sky appears blue due to Rayleigh scattering, where shorter violet and blue wavelengths scatter more and the eyes are sensitive to blue light.
• During sunset, the sun appears red because shorter wavelengths are scattered away while longer red wavelengths reach our eyes
• longer wavelengths pass through and are scattered when the sun traverses a greater distance through the atmosphere

Clouds

• Water droplets scatter the wavelengths of visible light, making clouds appear white, also known as Mie scattering.
• The clouds are dark and gray because the sunlight gets blocked by the cloud's thickness and height.