Waves and Optics (1)

CH 6 GENPHY2

Optics

Study of the behavior of visible light and other forms of electromagnetic waves

Larger

Electromagnetic Radiation (Visible Light) interacts with objects \______ than its wavelength

Rays

A straight line used to represent the motion of a light wave.

Ray Optics

The study of the movement of light photons (and lenses and mirrors)

Wave Optics

the study of light as a wave

Same size, smaller

Electromagnetic radiation interacts with objects about the \_____ \_____ as the wavelength or \______

TRUE

TRUE OR FALSE:
Visible light can never detect individual atoms \= smaller than its wavelength

Ray

Straight line that originates at some point and is perpendicular to wave fronts

Wave Fronts

a surface over which the phase of the wave is constant

Geometric Optics

the use of light rays to determine how light behaves when it strikes objects

1. Directly from the source through empty space
2. Through various media (medium)
3. After being reflected from a mirror

Three ways light can travel from source to another location

Ray Approximation

a simplification of light beams as
rays

Wave Propagation

* Rays point in the direction in the direction of the wave propagation
* Straight lines perpendicular to wave fronts

Reflection

the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through

Law of Reflection

the angle of incidence is equal to the angle of reflection

Angle of Incidence

the angle between the incident ray and the normal

Angle of Reflection

The angle between the reflected ray and the normal

Diffuse Reflection

angle of incidence varies; law of reflection still holds

Specular Reflection

a reflection produced by a smooth surface in which parallel light rays are reflected in parallel

Image

What is seen when the eyes look into a plane (flat) mirror

Virtual Image

Appears to be behind the mirror. Light does not go through it

Equal

Distance of the image (d0) from the mirror is \_____ to the distance of the object (di) from the mirror

Spherical Mirrors

mirrors in the shape of a portion of a sphere

Concave Mirror

A mirror that curves inward

Parallel

Rays from a faraway object are effectively \____

Convex Mirror

a mirror that curves outward

Spherical Aberration

Inability of spherical mirror to focus all parallel rays to a single point

Principal Axis

a straight line perpendicular to the surface of a mirror that divides the mirror in half

Center of Curvature

With curved mirrors, the center of the circle which the mirror is a part.

Focal Point

the point at which rays parallel to the optical axis reflect and meet

Focal Point

Where incident parallel rays come to a focus after reflection

Focal Length

the distance from the center of a lens to the focal point

Radius of Curvature

the distance between the center of curvature and the mirror's surface

Half

Focal length is \_____ of the radius of curvature

Ray Diagrams

diagram used to represent how light travels; each ray has an arrow to show the direction of travel

Mirror Equation

Relates the object and image distances to the focal length f

1/f \= 1/do + 1/di

Mirror Equation

Magnification of Image

height of the image divided by the height of the object

Sign Conventions

Give the correct locations and orientations of images as predicted by the ray diagrams

Positive

Image Height: Upright

Negative

Image Height: Inverted

In front

Distance is positive if: Image or object is \___ \____ of the mirror

Behind

Distance is negative if: Image or object is \______ of the mirror

Upright

Magnification is positive when t he image is \_____

Inverted

Magnification is negative when t he image is \_____

Diverge

to separate

Converge

to come together

Convex Mirrors

Reflected rays diverge. Seem to come from point F behind the mirror

FALSE

TRUE OR FALSE:
Convex mirrors always produce a REAL image

1. Virtual
2. Upright
3. Smaller

In convex mirrors, no matter where the object is placed on the reflecting side, the image will be:

Refraction

Bending of light s it passes one substance to another

Index of Refraction

* Ratio of the speed of light in vacuum to the speed of light in the medium
* a measure of the amount a ray of light bends when it passes from one medium to another

TRUE

TRUE OR FALSE"
The index of refraction is never less than 1.

Angle of Refraction

the angle between the refracted ray and the normal

Snell's Law

n1sinθ1 \= n2sinθ2

Total Internal Reflection

the complete reflection that takes place within a substance when the angle of incidence of light striking the surface boundary is less than the critical angle

Larger

Light passes into a medium with a smaller index of refraction \= \______ angle of refraction

Critical Angle

the angle of incidence that produces an angle of refraction of 90 degrees

No transmission occurs

In TIR, when an angle of incidence is larger than the critical angle...

Binoculars

real life example of TIR

Fiber Optics

thin glass fibers that use total internal reflection to carry light

Lenses

always refract

Thin lenses

Thickness is small compared to their radius of curvature

Convex Lenses

thicker at the center than at the edge

Concave Lenses

thinner in the middle than at the edge

Parallel Rays

converge at a focal point

Parallel Rays

Brought to a focus by converging lens. One thicker in the center than at the edge

Diverge

Diverging lens make parallel light \_______

Focal Point

the point at which rays parallel to the optical axis reflect and meet

1. Parallel to the axis
2. Through the focal point
3. Center of the lens

3 key rays

Ray comes in parallel to the axis

Exits through the focal point

Ray comes in through the focal point

Exits parallel to the axis

Ray goes through the center of the lens

Undeflected

Upright, Virtual

Three rays are also used for diverging lens
Images are:

Converging Lenses

Focal Length of Lens: Positive

Diverging Lenses

Focal Length of Lens: Negative

Same side

Object Distance (Lenses): Positive
Object on the \____ \____as the light entering the lens (except in compound systems)

Opposite Side

Image Distance (Lenses): Positive
Image is on the \_____ \_____ from the light entering the lens

Same Side

Image Distance (Lenses): Negative
Image is on the \_____ \_____ from the light entering the lens

Upright

Height of the image (Lenses): Positive

Inverted

Height of the image (Lenses): Negative

Energy

Light is an \______

Energy

* The ability to do work or cause change
* Can be carried from one place to another in two ways

1. By particles
2. By waves

Energy can be carried from one place to another in two ways:

1830

Most physicists had accepted the wave theory of light

End of 19th Century

Light was considered an electromagnetic wave

Early 20th Century

Light was shown to have a particle nature as well.

Christian Huygens

Dutch physicist who proposed the wave theory of light

Huygen's Principle

Developed for predicting the future position of wave front when an earlier position is known

Huygen's Principle

* Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself.
* The new wave front is the envelope of all the wavelets. The tangent to all of them

Wave Front

All the points along a two or three

No interference pattern would be observed

If the light traveled in a straight line after passing through the slits (Huygen's Principle)

Diffraction

The bending of a wave as it moves around an obstacle or passes through a narrow opening

Diffraction

Divergence of light from its initial line of travel

Diffraction

Bending of waves behind obstacles into the shadow region

Thomas Young

First demonstrated interference in light waves from 2 sources (1801)

Fringes

Bright and dark parallel bands

Constructive Interference

Amplitude of the resultant wave is greater than either individual wave

Destructive Interference

Amplitude of resultant wave is less than either individual wave

TRUE

TRUE OR FALSE:
Interference occurs as each point on the screen is not the same distance from both slits