Understanding light and its properties

• Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum
• Light is visible to the human eye
• Light is radiant energy
• Light is a type of energy that travels in the form of electromagnetic waves

Properties of Light

• Light has wave-particle duality
• Light exhibits properties of both waves and particles
• Light can be described as both a stream of particles, called photons, and as electromagnetic waves
• Light can be reflected, refracted, diffracted, and polarized, which are wave-like properties
• Light carries energy and momentum, which are particle-like properties
• Light travels at a constant speed in a vacuum
• The speed of light in a vacuum is approximately 299,792,458 meters per second (denoted as c)
• The speed of light can be reduced when it passes through a medium like air, water, or glass
• Wavelength is the distance between two successive crests or troughs of a wave
• Frequency is the number of waves that pass a given point per unit of time
• The energy of light is directly proportional to its frequency and inversely proportional to its wavelength
• Shorter wavelengths (e.g., blue light) have higher frequencies and higher energy
• Longer wavelengths (e.g., red light) have lower frequencies and lower energy

Electromagnetic Spectrum

• The electromagnetic spectrum encompasses all types of electromagnetic radiation
• The electromagnetic spectrum ranges from low-frequency radio waves to high-frequency gamma rays
• Visible light occupies a small portion of the electromagnetic spectrum
• The colors of visible light, in order of increasing frequency (decreasing wavelength), are red, orange, yellow, green, blue, indigo, and violet (ROYGBIV)
• Infrared radiation has lower frequency (longer wavelength) than red light
• Ultraviolet radiation has higher frequency (shorter wavelength) than violet light

Interaction of Light with Matter

• When light interacts with matter, it can be transmitted, absorbed, or reflected
• Transmission occurs when light passes through a material
• Absorption occurs when light's energy is taken up by the material, often converted into heat
• Reflection occurs when light bounces off the surface of a material
• The color of an object is determined by the wavelengths of light it reflects
• A red object reflects red light and absorbs other colors

Refraction

• Refraction is the bending of light as it passes from one medium to another
• Refraction occurs because the speed of light is different in different media
• The index of refraction (n) of a material is the ratio of the speed of light in a vacuum to the speed of light in the material
• Snell's Law describes the relationship between the angles of incidence and refraction
• Snell's Law: n1 * sin(θ1) = n2 * sin(θ2), where n1 and n2 are the indices of refraction of the two media, and θ1 and θ2 are the angles of incidence and refraction

Lenses

• A lens is a curved piece of transparent material that refracts light
• Converging lenses (convex) bring parallel rays of light to a focus
• Diverging lenses (concave) spread parallel rays of light apart
• The focal length (f) of a lens is the distance from the lens to the point where parallel rays converge (or appear to diverge from)
• The lens equation relates the object distance (do), image distance (di), and focal length (f) of a lens: 1/do + 1/di = 1/f
• Magnification (M) is the ratio of the image height to the object height: M = -di/do

Optical Instruments

• Optical instruments use lenses and mirrors to manipulate light and form images
• Examples of optical instruments include cameras, telescopes, microscopes, and the human eye
• A camera uses a lens to focus light onto a sensor or film
• A telescope uses lenses or mirrors to collect and focus light from distant objects
• A microscope uses lenses to magnify small objects
• The human eye uses a lens to focus light onto the retina