# Science 8 - Mirrors and Lenses

Term Definition
Plane mirror Regular, flat mirrors
Incident Ray Ray of light that travels toward a reflecting surface
Angle of Incidence The angel between the incident ray and the normal
Normal The line drawn from the point of incidence at 90 degrees to the surface of the optical device
Reflected Ray Ray of light that bounces off a reflecting surfaces
Angle of Reflection the angel between the reflected ray and the normal
Point of incidence The spot where the incident ray strikes the reflecting surface
Specular reflection The reflection of light off a smooth, shiny surface. Reflects a clear image.
Laws of reflection (2) 1. The angle of incidence equals the angle of reflection
2. The incident ray, normal and reflected ray all lie in the same plane.
Diffuse Reflection When light hits an irregular surface – you see a blurred image.
Real image Can be placed on a screen
Virtual image Cannot be placed on a screen – can only been seen looking through an optical device (like a lens)
Optical Device Produces an image of an object
What four characteristics are used to stud and compare images? 1. Size (smaller, large or same size as the object viewed), 2. Attitude (upright or upside down), 3. Location (Several choices such as on the side of the lens, opposite the object), 4. Type (real or virtual image)
Convex Mirror The mirror curves outwards towards the object (like the back of a spoon) – allows you to see more area; good for surveillance
Concave Mirror The mirror curves inwards (caves in) (like the inside of a spoon) – allows you to see things up close
Virtual or Real: Plane Mirror Virtual
Virtual or Real: Concave Mirror (Object closer than principal focus) Virtual
Virtual or Real: Convex Mirror Virtual
Virtual or Real: Concave Mirror (Object beyond principal focus) Real
Refraction The bending of light as it travels from one material into another
Angle of Refraction The angle between the refracted ray and the normal
Refracted Ray The ray of light that changes direction as it passes from one material into another
Lens A curved, transparent device that causes light to refract as it passes through
Principal Focus the position where parallel light rays come together
Focal Length The distance from the principal focus to the centre of the lens
Name three devices that use at least one lens Glasses, microscope, telescope, camera, contacts, binoculars
Optical telescopes collect visible light
Refracting telescopes Uses a series of convex lenses
Refleccting telescopes Uses mirrors and lenses (may be very large)