Understanding Lenses and Refraction

• Lenses are used in cameras, microscopes, telescopes, and spotlights to focus light and provide clear images
• Many people use spectacles with lenses to improve their vision

Refraction

• Lenses bend light as light passes through them
• Refraction occurs when light changes direction as it moves from one transparent substance to another, happening at the interface between the substances
• No directional change occurs if light passes through the interface at 90°

Refraction Cause

• Refraction happens because light travels at different speeds in different materials
• Light travels slower in substances like water or glass compared to air
• Light bends toward the normal when it enters glass or water from air, and away from the normal when exiting into air

Key Terms for Ray Diagram

• Normal: An imaginary line perpendicular to the surface at the point of incidence.
• Angle of Incidence: The angle between the incident ray and the normal.
• Angle of Refraction: The angle between the refracted ray and the normal.

Lenses Explained

• Lenses: Curved pieces of glass or transparent material
• Converging Lens: A lens that makes rays of light come together
• Focal Length: The distance between the center of the lens and the focal point

Converging Through Lenses

• Light bends towards the normal as t enters the lens and away from the normal as it leaves the lens
• Focal Point: Where the light rays meet after passing through a converging lens

Cameras Work

• Cameras use lenses to focus light and sensors to detect light, converting it into electrical signals stored on a memory card
• Aperture: An adjustable hole that controls the amount of light entering the camera, and a shutter stops light from hitting the sensor when the camera is not in use

Human Eye Overview

• Cornea: A transparent covering that focuses light as it enters the eye
• Lens: It focuses light
• Iris: The colored part of the eye that controls the size of the pupil to regulate the amount of light entering the eye

Two Types of Cells in the Retina

• Rod Cells: Detect low light levels but not different colors
• Cone Cells: Detect red, green, and blue light (primary colors)
• Combinations of cone colors form secondary colors, and a mix of all three creates white light

Light Movement

• Light: Transfers energy and travels faster than sound
• Vacuum: Light travels through this completely empty space, unlike sound
• Light Waves: Transverse and have a speed of 300,000,000 m/s in air
• Sound Waves: Longitudinal with a speed of 330 m/s in air

Rays of Light

• We can show how light travels by drawing rays
• Arrows indicate the direction of light travel

Material Interactions

• Transparent Materials: Light passes straight through (transmitted)
• Opaque Materials: Some light is reflected, and some is absorbed (warming the object)
• Translucent Material Examples: frosted glass, scattering light in different directions
• All surfaces subtly reflect light

Pinhole Cameras

• Small version of a camera obscura and demonstrate that light travels in straight lines
• The image forms upside down because light from the top of the object travels through the pinhole and ends up at the bottom of the screen, and vice versa

Mirrors Explained

• Made of glass with a thin, reflective metal layer at the back
• Specular Reflection: Light reflected evenly from smooth surfaces where the angle of reflection is the same as the angle of incidence
• Diffuse Reflection: Light scattered in all directions from rough surfaces

Images in Plane Mirrors

• Has left and right swapped over
• Same size as the object
• Same distance behind the mirror as the object is in front of it.

Light Spectrum

• White light is composed of different frequencies seen as different colors
• Rainbows and prisms split white light, separating colors through refraction (dispersion)
• Spectrum colors: red, orange, yellow, green, blue, indigo, and violet, with red refracted the least and violet the most

Making Colored Light

• Filters produce colored light by absorbing certain colors from white light
• Only the filter's color is transmitted/ let through