Physics 2 Ch12-13

compression

a region of high molecular density and high pressure

rarefaction

a region of lower density and air pressure

pitch

measure of how high or low a sound is perceived to be depending on the frequency of the sound wave

doppler effect

an observed change in frequency when there is relative motion between the source of waves and an observers

sine waves

represent the changes in air pressure due to the transmission of sound waves

frequency

number of cycles per unit of time (helps determine pitch)

audible sound waves

sound waves that an average human ear can hear (20 to 20,000 Hz)

(the frequency of audible sound waves determines how high or low we perceive sound)

infrasonic waves

sound waves with frequencies below 20 Hz

ultrasonic waves

sound waves with frequencies above 20,000

spherical waves

sound waves produced by very small sources diverge in the shape of a ‘V’

(represented graphically in 2 dimensions with series of circles surrounding the source)

wave fronts

they are circles that represent the centers of compression that surrounds the source

(each circle represents a spherical area)

rays

the radial lines perpendicular to the wave fronts

(distance between adjacent wave fronts = 1 wavelength)

(it indicates the direction of the wave motion)

plane waves

moving waves that have compressions in parallel straight lines

intensity

the rate at which energy flows throughout a unit area perpendicular to the direction of a wave motion

decibel (dB)

a dimensionless unit that describes the ratio of 2 intensities of sound; the threshold of hearing is commonly used as the reference intensity

resonance

a phenomenon that occurs when two objects naturally vibrate at the same frequency

relative intensity

the ratio of the intensity of a given sound wave to the intensity of the threshold of hearing

decibel level

used to measure loudness (dimensionless)

forced vibrations

the setting up of vibrations in an object by vibrating force

sympathetic vibrations

caused when an object vibrates as a reaction to sound waves that match its resonating frequency

natural frequency

the frequency at which an object vibrates when it is disturbed

fundamental frequency

the lowest frequency of vibration of a standing wave

harmonic series

a series of frequencies that includes the fundamental frequency and integral multiples of the fundamental frequency

timbre

the musical quality of a tone resulting from the combination of harmonics present at different intensities

beat

the periodic variation in the amplitude of a wave that is the superposition of 2 waves of slightly different frequencies.

(it’s the variation from soft to loud and back to soft)

electromagnetic wave

a wave that consists of oscillating electric and magnetic fields, which radiate outward from the source at the speed of light

wavelet

a small wave created as a result of a Huygens’s principle

Huygens’s Principle

every point on wavefront acts as a source of a secondary wavelets, and the new wavefront is the surface that touches all these wavelets

ray approximation

treating the propagation of light waves as though they move in straight lines perpendicular to the wave front

luminous flux

the rate at which light is emitted from a source (measured in lumens lm)

illuminance

the amount of light energy produced from the source that’s inversely proportional to the distance (measured in Joules)

reflection

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

angle of incidence

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

angle of reflection

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

virtual image

an image from which light rays appear to diverge, even though they are not actually focused there; a virtual image can’t be projected on a screen

diffuse reflection

the reflection of waves in many directions from a rough surface

ex: paper, cloth, unpolished wood

specular reflection

reflection of light off a smooth surface in only 1 direction

ex: mirror or water

flat / plane mirror

simplest mirror

concave spherical mirror

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

real image

an image that is formed by the intersection of light rays; a real image can be projected on a screen

convex spherical mirror

a mirror whose reflecting reflecting surface is an outward, curves segment of a sphere

radius of curvature

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

spherical aberration

inability of spherical mirrors to focus all parallel rays to a single point

paraxial rays

light rays that are very near the principal axis of the mirror

focal point

the point where parallel light rays converge after passing through a lens or reflecting off a mirror

focal length

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

magnification of the image

measure how large or small the image is with respect to the object’s original size

concave mirror with the object before c and f

concave with object on c

concave with object between c and f

concave with object at f

(no image formed)

concave with object after f (in front of it)

convex mirror

wave speed formula

f = c / wavelength

fundamental frequency

(open ended pipe & vibrating string)

f_n = (n)v/2L

fundamental frequency

(pipe closed at one end)

f_n = (n)v/4L

intensity formula

i = P/(4)(pi)(r²)

mirror equation

1/p + 1/q = 1/f

magnification formula

-q/p or h’/h