Light Waves Physics 1 L Mrs. Snapp

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 10 8 m/s in a vacuum.

Measuring Speed of Light

Using mirrors to measure speed of Light

Electromagnetic Radiation Radio, microwaves, infrared, visible, UV, Xray, gamma rays     increasing energy     Higher frequency = higher Energy

Other 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. Light is simply a way of referring to the visible portion of the electromagnetic spectrum. Long wavelength Low frequency Short wavelength High frequency

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.

Refraction Refraction occurs when a wave bends as it passes from one medium to another (crosses a boundary) at an angle. The wave bends because of the change in speed when it enters a different medium. Refracted ray water normal air Incident ray Boundary

Diffraction The bending of waves around the edge of a barrier or through an opening.

Reflection Reflection is when a wave changes directions because it encounters a barrier. rr barrier Normal Incident wave ii Reflected wave Law of Reflection:  i =  r “Angle of incidence = Angle of reflection”

Plane Mirrors Image in a flat “plane” mirror Same size as object Upright or erect Backwards Virtual Image is same distance behind the mirror as the object is in front of the mirror

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. (Fuzzy image)

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 f = R/2, where R is radius 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 = R/2, where R is radius of curvature

Focal Point CONCAVE MIRROR Parallel rays of light from a far object will converge at the focal point. CONVEX MIRROR Parallel rays of light from a far object will diverge as if they originated at the focal point.

Images in the Mirror Real Image Light rays actually converge at a point to form an image Will always be inverted or upside down Image is formed in front of the mirror; therefore the image can be projected onto a screen Ex: in a concave mirror or spoon – “real” image is upside down until you move in to focal point and it flips Virtual Image An image formed by light rays that only appear to intersect Ex: what you see in a plane mirror – the image you see looks like its behind the mirror and its right side up

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

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

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

Ray Diagram Concave Mirror (object inside f) f C object image Draw 2 rays from tip of object: 1) parallel, then through f, extend reflected ray behind mirror. 2) through f as if it came from focal point, then parallel, extend reflected ray behind mirror Image is virtual, erect, & magnified

Cf Ray Diagram Convex Mirror object image 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 is virtual, erect, & reduced

Calculations f = focal length d o = object distance d i = image distance h i = image height h o = object height M = magnification

Interpreting Calculations Focal length (f) converging, then f = +diverging, then f = - Image distance (d i ) d i =+, then image is real d o = -, then image is virtual Magnification (M) M = +, image is erect M = -, image is inverted

Luminous vs I lluminated Luminous a body that emits light has luminous flux I lluminated body that reflects light no luminous flux does not emit light of its own

Brightness and distance from light source A luminous source emits light energy at a certain rate. The brightness on the illuminated object will vary inversely with the square of the distance.

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  or cd = lm / 4  Intensity = Flux or Power in lumens  4 pi