Transcript Light
A. Light is a wave that carries energy; a light wave emits a countless number of light rays in all directions 1. The material through which a wave travels is called a medium 2. Light is an electromagnetic wave that does not need a medium in which to travel B. For the eyes to see an object light must strike the object and bounce off in a process called reflection 1. Opaque – materials that let no light pass through them 2. Transparent – let almost all light pass through 3. Translucent – let some, but not all, light pass through C. White light is composed of different wavelengths which have colors ranging from red to violet 1. Objects appear to have different color because they absorb some light waves and reflect others a) An object appears the color of light it reflects 2. Three primary colors of light – red, blue and green a) All visible colors can be made by mixing the 3 primary colors of light 3. Three primary pigment colors – yellow magenta and cyan a) Pigments are materials like paint that are used to change the color of objects A. Law of Reflection – the angle of incidence is equal to the angle of reflection 1. Regular Reflection – results as light bounces off a smooth surface such as a mirror 2. Diffuse Reflection – uneven reflection of light waves from a rough surface a) Scattering – when light waves traveling in one direction are made to travel in many different directions B. Mirrors 1. Plane Mirror – reflects an actual size image that seems to be behind the mirror due to the way the brain interprets light 2. Concave Mirrors – cause light rays to converge (come together) a) Light waves travel parallel to the optical axis and reflect through the focal point b) Focal length – the distance along the optical axis from the mirror to focal point c) The image formed depends on the position of the object relative to the focal point If closer than one focal length image will be upright but magnified If further than one focal length image will be upside-down d) A beam of light can be produced when a light source is placed at the mirrors focal point 3. Convex Mirror – Cause light waves to diverge (spread out) a) Image formed will be upright but smaller than the actual size b) Often used for security mirrors in stores and side rearview mirrors on cars A. Refraction – the bending of waves caused by a change in speed as they pass through different media 1. Speed of Light a) In empty space = 300,000 km/s or 300,000,000 m/s b) It travels more slowly when it travels through matter such as air, water or glass B. Lens – transparent object with at least one curved side that causes light to bend 1. Convex Lens – thicker in the center than at the edges; converges light a) Forms an image based of how far the object is from the focal point 2. Concave Lens – thicker at the edges than at the middle; diverges light a) Forms an image upright but smaller than the actual object C. Total Internal Reflection – when all of the light waves striking the boundary between 2 transparent materials are reflected rather than any being refracted 1. A window exhibits partial reflection – some waves reflect others pass through 2. Total reflection depends on achieving the critical angle for materials involved A. Microscopes 1. Compound Microscopes – Use 2 convex lenses, the objective lens and eyepiece lens, to magnify an image B. Telescopes 1. Refracting Telescope – uses 2 convex lenses, objective & eyepiece to form an image of a distant object 2. Reflecting Telescope – uses a concave mirror to focus light onto a secondary mirror that directs the image to the eyepiece C. Cameras 1. Film Camera – uses a convex lens to form an inverted image on light sensitive film D. Lasers 1. Unlike ordinary light a laser beam doesn’t spread out as it travels 2. Uses only one wavelength (color) of light so that the crests and troughs don’t overlap a) Large amounts of energy can be applied to small areas b) Can replace scalpels in surgery