Physics Light and Optics

Electromagnetic wave

A wave that consists of oscillating electric and magnetic fields, which radiate outward from the source at the speed of light, transverse waves, spectrum includes more than visible light

Light is

A form of electromagnetic radiation

Visible light

Electromagnetic radiation that is visible to the human eye, visible light has a wavelength in the range of approximately 380 nm to about 740 nm. These are wavelengths between the invisible infrared, with longer wavelengths and the invisible ultraviolet, with shorter wavelengths

Electromagnetic waves vary depending on

Frequency and wave length

Illuminance decreases as the

Square of the distance from the source

Luminous flux (lumens) (ln)

The rate at which light is emitted from a source

Light traveling through a uniform substance, whether it is air, water, or a vacuum is

Always travels in a straight line

Reflection is

The change in direction of an electromagnetic wave at a surface that causes it to move away from the surface

Specular reflection

Reflection is reflection from a smooth, shiny surface such as a mirror or a water surface

Diffuse reflection

Reflection from a rough, texture surface such as paper or unpolished wood

The angle of incidence

The angle between a ray that strikes a surface and the line perpendicular to that surface at the point of contact

The angle of reflection

The angle formed by the line perpendicular to a surface and the direction in which a reflected ray moves

The angle of incidence and the angle of reflection are

Always equal

The two parts of the law of the reflection

1. The angle of incidence is equal to the angle of reflection

2. The incident ray, normal, and the reflected ray are all in the same plane.

Flat mirrors

Form virtual images that are the same distance from the mirror's surface as the object is

Virtual image

The image formed by rays that appear to come from the image point behind the mirror but never really do, can never be displayed on a physical surface

Concave spherical mirror

A mirror whose reflecting surface is a segment of the inside of a sphere

Concave mirrors

Can produce real or virtual images, used whenever a magnified image of an object is needed (ex. dressing table mirror)

Real image

An image formed when rays of light actually pass through a point on the image. Real images can be projected onto a screen.

Convex spherical mirror

A mirror whose reflecting surface is outward-curved segment of a sphere

Light rays diverge upon reflection from a convex mirror,

Forming a virtual image that is always smaller than the object

Flat mirrors

Creates virtual image, location object distance is equal to image distance, same size of the object

Concave mirrors

Creates virtual or real image, location determined by mirror equation, size of image determined by magnification equation

Convex mirrors

Creates virtual image, location of image determined by mirror equation, size of image determined by magnification equation

Spherical aberration

Images created by spherical mirrors, occurs when parallel rays far from the principal axis converge away from the mirrors focal point

Parabolic mirrors

Eliminate spherical aberration, all parallel rays converge at the focal point of a parabolic mirror

Two types of telescopes that use visible light

1. Reflecting telescope - Uses parabolic mirrors to form an image

2. Refracting telescope - Uses a combination of lenses to form an image

Virtual image

Appears behind mirror, light rays do not pass through it, cannot be projected

Real image

Appears in front of mirror, light rays pass through it, can be projected

Because white light can be dispersed into its elementary colors,

It is reasonable to suppose that elementary colors can be combined to form white light

Additive primary colors

Produce white light when combined

Light of different colors can be produced by

Adding light consisting of the primary additive colors (red, green, and blue)

Subtractive primary colors

Filter out all light when combined

Pigments can be produced by

Combining subtractive colors (magenta, yellow, and cyan)

Linear polarization

The alignment of electro-magnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other

Light can be linearly polarized through

Transmission, reflection, refraction or scattering

Transmission

The line along which light is polarized is called the transmission axis of that substance

Reflection off water

Such a reflection will be partially polarized. Polarized sunglasses make use of this; they are polarized in the opposite direction to cut glare

Effect of polarizers on digital watches

LCD displays work by having a polarizer just above a liquid crystal cell. When an electric field is applied to the liquid crystal, it polarizes light at 90 to the permanent polarizer, and blocks the light. This is what makes the black numbers seen on the display. If you look at a digital watch through a polarizer, it will be completely black at certain angles

Light can be polarized by

Reflection, refraction and scattering

At a particular angle,

Reflected light is polarized horizontally

The sunlight scattered by air molecules is

Polarized for an observer on Earth's surface

Refraction occurs when

A beam of light passes from one material into another material. At the surface of the two materials, the path of the beam changes its direction. The refracted beam acquires some degree of polarization in a plane perpendicular to the surface