Light

Light Light is an electromagnetic wave. It is considered to be oscillating electric and magnetic fields.

Light However, Some experiments done in the early 20th century showed light behaving as a particle rather than a wave. So light can also be thought of as a packet of energy called a PHOTON!

Light The speed of light is roughly 3 x 108 m/s The formula for speed of light is the same for speed of sound, expect we use the letter C to represent speed of light. c = fλ

Light Intensity is the amount of light illuminating a surface. Lumens: the number of photons per second that fall on a given area. The units for Lumens are Lux: equal to one lumen per square meter.

Light If we just want to measure the Power (remember energy over time) then we just use the photons Per second and not the area.

Light Light has a large range of frequencies, of which we only se a small portion.

Color The colors we see are the frequencies of visible light that are reflected off the object.

Light Light diffracts just like sound. We can use straight arrows to show the direction of the waves. This ray approximation was created by Christian Huygens and is called the Huygens principal.

Light Light refracts: When light waves pass from one material to another they bend.

Light Reflection is when a surface bounces light off of it. There is no surface that reflects 100% of the light.

Light The surface of the material will determine how the light is reflected. A rough surface will reflect the light in many different directions. A smooth surface will reflect all the light in the same direction.

Light For a flat mirror we draw a perpendicular line from the mirror. This is called the normal.

Light The angle between the incoming light ray and the normal is called the angle of incidence. The angle between the reflected ray and the normal is called the angle of reflection.

Light The angles of incidence and reflection are equal.

Light The image that appears in the mirror, but is not really there is called the virtual image.

Mirrors Concave mirrors are the inside of a sphere. Mirrors that curve inward.

Mirrors A convex mirror is the outside of a sphere. It bulges outward

Mirrors For Concave Mirrors the light from the object is reflected back toward the object. Because this image can be projected on a screen it is called a Real Image.

Mirrors For all concave mirrors there is a imaginary line that extends through the center of the curvature. This is called the Principal Axis

Mirrors All light striking a concave mirror is reflected away from the image and will pass through a focal point. This causes the real image to be upside down.

Mirrors The distance from the back of the mirror to the object is called p. The distance from the back of the mirror to the image is called q

Mirrors If we add the two together we get the focal length. The point where all the light rays converge.

Mirrors Formula 1/p + 1/q = 1/f

Mirrors Magnification is the ratio of the image height to the object height. It is also the ratio of the image distance to object distance only negative.

Mirrors Formula: M =

Mirrors Any height that is below the principal axis is a negative height.

Mirrors Convex Mirrors bulge outward. The rays that strike the mirrors surface diverge.

Mirrors Since no image can be projected the image is virtual. The image appears to be inside (or behind) the mirror, so the distance to the image is negative.

Mirrors This means that the focal point also appears to be inside (behind) the mirror and so the focal point distance is negative as well.

Mirrors Magnification for convex mirrors is always less than 1. Meaning objects a appear smaller.

Mirrors Since the image is above the principal axis the height of the image is positive.

Mirrors For both mirrors any image produced is slightly blurry. This is called spherical aberration. The more perfectly parabolic the mirror the less spherical aberration there is.

Lenses When light hits a new medium it bends. This is called Refraction. The reason it bends is because it changes velocity.

Lenses Every transparent substance will change the velocity of light differently. The index of refraction is the ratio between the speed of light in a vacuum and the speed of light in the medium.

Lenses Index of Refraction The symbol is an “n”, but there are no units. n = c/v

Lenses How much the light bends is called the Angle of Refraction. To determine this angle we have to draw a line perpendicular to the medium called the Normal.

Lenses Snell’s Law: nisinθi = nrsinθr We can use the index of refraction for the substance and the angle of the incident ray to determine the angle of the refracted ray.

Lenses Refraction is the reason lenses work to produce an image. There are two types of lenses. Converging Diverging

Lenses For both lenses we measure everything from the center of the lenses. Converging bends the light to a focal point on the axis. Diverging bends the light away from the axis

Lenses Each color of light has a different wave length and speed. When light passes through a medium each wavelength bends a little bit differently and we see a rainbow.