Light and Reflection

Characteristics Light is a transverse wave. Light waves are electromagnetic waves--which means that they do NOT need a medium to travel. ALL Electromagnetic waves travel with a speed of 3.0 x 108 m/s in a vacuum. Light waves behave like other waves and have the same characteristics such as amplitude, frequency, and wavelength. The “brightness” or intensity follows the inverse square relationship.

Characteristics of EM Waves continued Made up of 2 components electric field & magnetic field The electric and magnetic fields are perpendicular to each other. A changing electric field will create a magnetic field and a changing magnetic field will create an electric field; therefore the wave propagates itself through space without need of a medium.

Other Electromagnetic Waves Radio Microwaves Infrared Ultraviolet X-rays Gamma Rays Radar All of these follow the same rules as Light and travel at the same speed. Light is simply a way of referring to the visible portion of the electromagnetic spectrum.

Reflection & Mirrors

Law of Reflection i incident ray reflected ray normal Mirror surface r Angles are always measured from the normal, never the surface Angle of incidence equal angle of reflection i = r

Types of Reflection Specular (regular) Reflection Diffuse Reflection When parallel rays of light fall on a smooth surface they are reflected parallel from the surface. Diffuse Reflection When parallel rays of light fall on a textured surface they are reflected in many different directions. They are diffused.

Types of reflection (cont)

Plane (flat) mirrors Plane mirrors produce images that are: virtual same size (M = 1) upright located behind the mirror

Spherical (curved) mirrors

Concave Mirrors Reflective surface to the inside of curve, forms a “cave” Parallel rays of light from a far object will converge at the focal point. Concave Mirrors also called “converging mirrors” Focal point is half the distance from the center of curvature (C) to the mirror The center of curvature is equal to the radius f = C/2, where C is center of curvature

Convex Mirrors Reflective surface to the outside of curve (back of spoon) Parallel rays of light from a far object will diverge as if they originated at the focal point. Convex Mirrors also called “diverging mirrors” Focal point is half the distance from the center of curvature (C) to the mirror f = C/2, where C is center of curvature

Calculations f = focal length do = object distance di = image distance hi = image height ho = object height M = magnification

Using signs correctly Focal length (f) concave, then f = + convex, then f = - Image distance (di) di=+ , then image is real do= -, then image is virtual Magnification (M) M = +, image is erect M = - , image is inverted

Ray Diagram Concave Mirror Draw 2 rays from tip of object: 1) parallel, then through f 2) through f, then parallel object Image is real, inverted, & reduced image C f

Ray Diagram Convex Mirror Draw 2 rays from tip of object: 1) parallel, then reflect as if ray came from f, 2) toward focal point, then parallel, extend reflected ray behind mirror image object f C Image is virtual, erect, & reduced

Web-based animation for curved mirrors Concave mirrors http://www.csupomona.edu/~bmhoeling/ReflectionMirrors/ReflectionMirrors8.html Convex mirrors http://www.csupomona.edu/~elearning/assets/learningobjects/optics/convexmirror/