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Light Waves Physics 1 H Created by Stephanie Ingle Light • Light is a transverse wave. • Light waves are electromagnetic waves--which means that they do NOT need a medium to travel. • Light waves behave like other waves and have the same characteristics such as amplitude, frequency, and wavelength. Characteristics of Light • Intensity (brightness) -- represented by amplitude • Color -- determined by frequency • Wave speed - depends on the medium • Light waves as well as ALL Electromagnetic waves travel with a speed of 3.0 x 108 m/s in a vacuum. Characteristics of Electromagnetic Waves • 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. Electromagnetic Waves • • • • • • • Radio Microwaves Infrared Visible Light Ultraviolet X-rays Gamma Rays • All of these follow the same rules as Light and travel at the same speed. • They are listed in order of increasing frequency and energy and decreasing wavelength • Light is the visible part of the spectrum Luminous vs Illuminated • Luminous – a body that emits light – has luminous flux • Illuminated – a body that reflects light – no luminous flux – does not emit light of its own Luminous Flux (P) • Luminous flux is the rate at which light energy is emitted from the source. • Equivalent to Power • Measured in lumens (lm) Luminous Intensity (I) • The amount of light (luminous flux) that falls on one square meter at a distance of 1 meter from the source. • Equivalent to Intensity at r = 1 m • Measured in candelas (cd) I P 4 P I 4 Illuminance (E) • Amount of light that falls on a surface • Intensity of light at any given distance from source • measured in lux r • lux = lumen/m2 P E 2 4 r bulb Reflection & Mirrors Law of Reflection normal incident ray Mirror surface reflected ray i r • Angles are always measured from the normal, never the surface • Angle of incidence equal angle of reflection • i = r Types of Reflection • Regular 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. Concave Mirrors • Reflective surface, like inside of a spoon, 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 • f = R/2, where R is radius of curvature Convex Mirrors • Reflective surface, like back of a spoon or outside of curve • 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 = R/2, where R is radius of curvature Calculations 1 1 1 f do di h i d i M ho do f = focal length do = object distance di = image distance hi = image height ho = object height M = magnification Interpreting Calculations Focal length (f) concave or converging, then f is + convex or diverging, then f is Image distance (di) di is + , then image is real di is -, then image is virtual Magnification (M) M = +, image is erect and virtual M = - , image is inverted and real Ray Diagram Concave Mirror (object beyond C) Draw 2 rays from tip of object: 1) parallel, then through f 2) through f, then parallel The image is formed where the reflected rays intersect. object Image is real, inverted, & reduced image C f Ray Diagram Concave Mirror (object at C) Draw 2 rays from tip of object: 1) parallel, then through f 2) through f, then parallel object Image is real, inverted, & same size C image f Ray Diagram Concave Mirror (object between f & C) Draw 2 rays from tip of object: 1) parallel, then through f 2) through f, then parallel Image is real, inverted, & magnified object C image f Ray Diagram Concave Mirror (object inside f) Draw 2 rays from tip of object: 1) parallel, then through f 2) as if it came from the focal point and then parallel 3) extend the reflected rays behind mirror to locate image image C f object Image is virtual, erect, & magnified Ray Diagram Convex Mirror Draw 2 rays from tip of object: 1) parallel, then reflect as if ray came from focus 2) toward the focal point, then parallel 3) extend the reflected rays behind the mirror to locate the image object Image is virtual, erect, & reduced image f C