Physics: Mirrors

ray optics

the study of light

How does light travel?

in a straight line

How can a ray change direction?

refractions + reflection

luminous

a source that emits light (ex: the sun)

illuminated

a source that reflects light (ex: the moon)

opaque

a material that does not allow any light to pass through; may reflect some light

transparent

a material that transmits light; may reflect some light

translucent

a material that filters light; may reflect some light

luminous flux (P)

rate light is emitted

lumens (lm)

unit of measurement of luminous flux

illuminance (E)

rate light strikes a surface

lux (lx)

lumens per square meter

inverse-square law

as square of the distance increases, the number of rays illuminating an area decreases

luminous intensity

the luminous flux that falls on the inside of a 1m radius sphere

candela (cd)

unit of measurement of luminous intensity

How can intensity be increased?

brighter light and/or decreased distance

diffraction

the bending of light around a barrier

white

appears when an object reflects all visible light

black

appears when an object absorbs all visible light

When does color arise?

when certain wavelengths are absorbed while others are reflected; the reflected wavelengths are the colors that we can see

refraction

when light passes from one medium to another with a different density, different colors, or bent at a different angle

polarization

a process that forces light into a single plane of oscillation; reduces intensity by 50%

Doppler effect

an increase or decrease in wavelength as the observer moves toward or away from an object emitting the wave

blue shift

a negative change in wavelength, frequency increases

red shift

a positive change in wavelength, frequency decreases

Law of Reflection

when a ray of light hits a perfectly smooth surface, it bounces off it at an equal angle to the one that came in

the normal

the line perpendicular to the surface (represented by a dotted line)

angle from the normal to the surface

90 degrees

specular reflection

• light reflected from a smooth surface at a definite angle

• light rays are reflected in a parallel

• image is preserved

diffuse reflection

• produced by rough surfaces that tend tp reflect light in all directions

• more common than specular reflection

angle between the incident ray and the reflected ray

(angle between normal & ray of reflection/incidence) \* 2

plane mirror

flat surface that produces a virtual image of the real object, requires at least 2 rays

How is an image created?

• By rays of light that travel from the object to the mirror

• Reflected rays diverge causing an image to form “behind” the mirror

virtual image

• images of real objects produced by plane mirrors

• formed when reflected rays do NOT meet

What happens to the size of the image when it is reflected in a plane mirror?

the dimensions stay the same as the real object

image position & height

are preserved in a reflection (same as real object)

type of image that convex mirrors form

virtual

speed of light & main scientists

Galileo, Ole Roemer, & Albert Michelson

electromagnetic spectrum

radio → microwave → infrared → visible (ROYGBIV) → ultraviolet → xray → gamma

center of curvature (c)

the radius of the geometric center of the sphere that it is a piece of

focal point

halfway to the center of curvature.  Where incident rays that are parallel to the principal axis converge after reflecting.

focal length

• position of the focal point with respect to the mirror along the principal axis. Positive value with concave mirror.

• f = *r/*2

principle axis

a straight line perpendicular to the surface of the mirror that cuts it in half.