AP Physics 2 unit 6

Visible light

One type of electromagnetic (EM) radiation that represents a tiny portion of the whole EM spectrum.

Electromagnetic radiation

Radiation that is transferred by waves that can interact with each other.

Wave optics

The study of the effects of interaction with matter and interference with other waves.

amplitude

the height, or magnitude, of an electromagnetic wave

coherent

waves are in phase or have a definite phase relationship

constructive interference

when two waves arrive at the same point exactly in phase; that is, the crests of the two waves are precisely aligned, as are the troughs

constructive interference for a diffraction grating

occurs when the condition 𝑑sin𝜃=𝑚𝜆( for 𝑚=0,1,-1,2,-2,…) is satisfied, where 𝑑 is the distance between slits in the grating, 𝜆 is the wavelength of light, and 𝑚 is the order of the maximum

constructive interference for a double slit

the path length difference must be an integral multiple of the wavelength

converging lens

a convex lens in which light rays that enter it parallel to its axis converge at a single point on the opposite side

converging mirror

a concave mirror in which light rays that strike it parallel to its axis converge at one or more points along the axis

critical angle

incident angle that produces an angle of refraction of 90º

destructive interference

when two identical waves arrive at the same point exactly out of phase; that is, precisely aligned crest to trough

destructive interference for a double slit

the path length difference must be a half-integral multiple of the wavelength

destructive interference for a single slit

occurs when 𝐷 sin𝜃 = 𝑚𝜆,(for 𝑚=1,-1,2,-2,3,…) where 𝐷 is the slit width, 𝜆 is the light's wavelength, 𝜃 is the angle relative to the original direction of the light, and 𝑚 is the order of the minimum

dispersion

spreading of white light into its full spectrum of wavelengths

diverging lens

a concave lens in which light rays that enter it parallel to its axis bend away (diverge) from its axis

diffraction

the bending of a wave around the edges of an opening or an obstacle

diffraction grating

a large number of evenly spaced parallel slits

electromagnetic spectrum

the full range of wavelengths or frequencies of electromagnetic radiation

focal length

distance from the center of a lens or curved mirror to its focal point

focal point

for a converging lens or mirror, the point at which converging light rays cross; for a diverging lens or mirror, the point from which diverging light rays appear to originate

frequency

the number of complete wave cycles (up-down-up) passing a given point within one second (cycles/second)

infrared radiation (IR)

a region of the electromagnetic spectrum with a frequency range that extends from just below the red region of the visible light spectrum up to the microwave region, or from 0.74𝜇𝑚 to 300𝜇𝑚

index of refraction

for a material, the ratio of the speed of light in vacuum to that in the material

incoherent

waves have random phase relationships

law of reflection

angle of reflection equals the angle of incidence

longitudinal wave

a wave in which the disturbance is parallel to the direction of propagation

magnification

ratio of image height to object height

microwaves

electromagnetic waves with wavelengths in the range from 1 mm to 1 m; they can be produced by currents in macroscopic circuits and devices

periodic motion

motion that repeats itself at regular time intervals

ray

straight line that originates at some point

real image

image that can be projected

refraction

changing of a light ray's direction when it passes through variations in matter

superposition

the phenomenon that occurs when two or more waves arrive at the same point

thin film interference

interference between light reflected from different surfaces of a thin film

transverse wave

a wave, such as an electromagnetic wave, which oscillates perpendicular to the axis along the line of travel

virtual image

image that cannot be projected

ultra-high frequency (UHF)

TV channels in an even higher frequency range than VHF, of 470 to 1000 MHz

ultraviolet radiation (UV)

electromagnetic radiation in the range extending upward in frequency from violet light and overlapping with the lowest X-ray frequencies, with wavelengths from 400 nm down to about 10 nm

very high frequency (VHF)

TV channels utilizing frequencies in the two ranges of 54 to 88 MHz and 174 to 222 MHz

visible light

the narrow segment of the electromagnetic spectrum to which the normal human eye responds

wave

a disturbance that moves from its source and carries energy

wave velocity

the speed at which the disturbance moves

Wavelength

The distance from one peak to the next in a wave.

Wavelength in a medium

𝜆n = 𝜆/𝑛 where 𝜆 is the wavelength in vacuum, and 𝑛 is the index of refraction of the medium.

X-ray

Invisible, penetrating form of very high frequency electromagnetic radiation, overlapping both the ultraviolet range and the 𝛾 ray range.

Wave

A disturbance that propagates, or moves from the place it was created.

Wave period (T)

The time for one complete up and down motion of a wave.

Wave frequency (f)

The number of cycles per unit time, calculated as 𝑓=1/𝑇.

Wave velocity (𝑣w)

The speed at which the disturbance moves, also called propagation velocity or propagation speed.

Mechanical waves

Waves that need a medium through which they travel.

Electromagnetic waves

Waves that can travel in the absence of a medium of propagation.

Transverse wave

A wave where the disturbance is perpendicular to the direction of propagation.

Longitudinal wave

A wave where the disturbance is parallel to the direction of propagation.

Superposition

The phenomenon where two or more waves arrive at the same point and their disturbances are superimposed.

Constructive interference

When two identical waves arrive at the same point exactly in phase, producing a wave with twice the amplitude of the individual waves.

Destructive interference

When two identical waves arrive exactly out of phase, producing a resulting amplitude of zero.

Standing wave

A wave formed by the superposition of two or more moving waves that appear to vibrate in place.

Electromagnetic wave characteristics

An electromagnetic wave has a frequency and a wavelength associated with it and travels at the speed of light, or 𝑐.

Propagation speed relationship

The relationship among wave characteristics can be described by 𝑣W = 𝑓𝜆.

Speed of light (c)

The speed at which all electromagnetic waves travel, defined by the equation 𝑐 = 𝑓𝜆.

Electromagnetic Spectrum

The various types of electromagnetic waves categorized according to their wavelengths and frequencies.

High-frequency electromagnetic waves

More energetic and able to penetrate better than low-frequency waves.

Information capacity of electromagnetic waves

High-frequency electromagnetic waves can carry more information per unit time than low-frequency waves.

Wavelength and detail resolution

The shorter the wavelength of any electromagnetic wave probing a material, the smaller the detail it is possible to resolve.

Transmission, reflection, and absorption

When an electromagnetic wave impinges on a material, it can be transmitted, reflected, or absorbed, including partial cases.

Ray Aspect of Light

Light travels in straight lines called rays, originating from a source to another location.

Light travel through media

Light can travel through various media, such as air and glass, to reach a person.

Reflection of light

Light can arrive after being reflected, such as by a mirror.

Definition of a ray

A ray is a straight line that originates at some point.

Light interaction with objects

When light interacts with objects several times as large as its wavelength, it travels in straight lines and acts like a ray.

Wavelength of light

The wavelength of light is less than a micron (a thousandth of a millimeter).

Geometric optics

The part of optics where the ray aspect of light dominates, described by geometry and simple trigonometry.

Law of Reflection

The angle of reflection equals the angle of incidence, measured with respect to a normal to the surface.

Law of Refraction

Refraction is the changing of a light ray's direction when it passes through variations in matter.

Refraction phenomena

Refraction is responsible for a range of optical phenomena, from lenses to voice transmission through optical fibers.

Index of Refraction

The index of refraction 𝑛 of a material is defined to be 𝑛 = 𝑐/𝑣, where 𝑣 is the observed speed of light in the material.

Speed of light in matter

The speed of light is always less than 𝑐 in matter and equals 𝑐 only in a vacuum.

Index of refraction value

The index of refraction is always greater than or equal to one.

Change in speed of light

The change in the speed of light is related to the indices of refraction of the media involved.

Law of Refraction

The exact mathematical relationship stated in equation form as 𝑛1sin𝜃1=𝑛2sin𝜃2.

Indices of Refraction

𝑛1 and 𝑛2 are the indices of refraction for medium 1 and 2.

Incident Ray

The incoming ray that strikes the boundary between two materials.

Refracted Ray

The outgoing ray that is bent as it passes into a different medium.

Incident Angle

The angle between the incident ray and the perpendicular to the surface at the point of incidence.

Refracted Angle

The angle between the refracted ray and the perpendicular to the surface at the point of refraction.

Critical Angle (𝜃𝑐)

The incident angle 𝜃1 that produces an angle of refraction of 90º.

Total Internal Reflection

Occurs when the incident angle 𝜃1 is greater than the critical angle 𝜃𝑐, resulting in all light being reflected back into medium 1.

Critical Angle Formula

𝜃𝑐 = sin−1 ( 𝑛2/𝑛1 ) for 𝑛1 > 𝑛2.

Convex Lens

A lens that converges light rays that enter it parallel to its axis to a single point on the opposite side.

Focal Point (F)

The point at which light rays cross after passing through a convex lens.

Focal Length (𝑓)

The distance from the center of the lens to its focal point.

Concave Lens

A diverging lens that causes light rays to bend away from its axis.

Ray Tracing

The technique of determining or following the paths that light rays take.

Thin Symmetrical Lens

A lens that has two focal points, one on either side, both at the same distance from the lens.

Ray Behavior in Converging Lens

A ray entering a converging lens parallel to its axis passes through the focal point F of the lens on the other side.

Ray Behavior in Diverging Lens

A ray entering a diverging lens parallel to its axis seems to come from the focal point F.

Image Distance (si)

The distance of the image from the center of a lens.

Object Distance (so)

The distance of an object from the center of a lens.

Height of Object (ℎo)

The height of the object.