Waves – Mechanical & Electromagnetic
WAVE PROPERTIES:





Wave – rhythmic disturbance that carries energy through matter and space
All waves transmit energy
Some waves you cannot see
Medium – what a wave moves through (ex: water, string, air)
Wave pulse – single bump or disturbance of a wave
2 TYPES OF WAVES:
 Transverse Wave – wave that vibrates perpendicular to the direction of
wave motion (ex: rope, electromagnetic waves)
 Longitudinal or Compression waves – wave in which the disturbance of the
medium is in the same direction as the motion of the wave (ex: sound
waves, slinky waves)
 Surface Waves – have both longitudinal and transverse wave properties
MEASURING A WAVE:
 Velocity (speed) – distance/time (d/t) – speed of the wave depends only on
the medium it travels through
-Also,
v=λxf
velocity
wave length
frequency
 Amplitude – maximum amount of displacement from its equilibrium (rest)
position
-more amplitude = more energy transferred by each wave
 Crests – high points
 Troughs – low points
 Wavelength (λ) – shortest distance between points where the wave pattern
repeats itself
Waves – Mechanical & Electromagnetic
 Frequency (f) – number of oscillations (repetitions) per second
 Measured in Hertz (Hz), which stands for “times per second”
 f = 1/T
 Period (T) – think “time period”, the time it takes for one wave to begin to
repeat itself.
 T = 1/f
WAVE DIAGRAMS:
PARTS OF A WAVE:
TRANSVERSE VS. LONGITUDINAL WAVES:
Waves – Mechanical & Electromagnetic
Examples:
1. A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a
frequency of 51.2 Hz and a distance from a crest to the neighboring trough of 12.8 cm.
Determine the period of such a wave.
2. Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing
flapping is ____ sec.
3. A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of
her pacing is ________ Hz.
4. Non-digital clocks (which are becoming more rare) have a second hand that rotates around in
a regular and repeating fashion. The frequency of rotation of a second hand on a clock is
_______ Hz.
5. Olive Udadi accompanies her father to the park for an afternoon of fun. While there, she hops
on the swing and begins a motion characterized by a complete back-and-forth cycle every 2
seconds. The frequency of swing is _________.
Waves – Mechanical & Electromagnetic
6. In problem #5, the period of swing is __________.
7. A period of 5.0 seconds corresponds to a frequency of ________ Hertz.
8. A common physics lab involves the study of the oscillations of a pendulum. If a pendulum
makes 33 complete back-and-forth cycles of vibration in 11 seconds, then its period is ______.
9. A child in a swing makes one complete back and forth motion in 3.2 seconds. This statement
provides information about the child's
10. The period of the sound wave produced by a 440 Hertz tuning fork is ___________.
11. As the frequency of a wave increases, the period of the wave ___________.
Waves – Mechanical & Electromagnetic
WAVE BEHAVIOR:
Incident Wave – An incoming wave that strikes the boundary between to media.
Reflected Wave – A returning wave that is either inverted or displaced in the
same direction as the incident wave.
**NOTE: Law of Reflection: The angle between the incident ray and the normal
will always equal the angle between the reflected ray and the normal.
Interference and the Principle of Superposition – The interaction of two or more
rays. The displacement of a medium caused by two or more waves is the algebraic
sum of the displacements of the individual waves.
Constructive Interference – Superposition of waves resulting in increased wave
displacement.
Destructive Interference – Superposition of waves with opposite but equal
amplitudes.
Standing Wave – A wave with stationary nodes and antinodes. A wave that stays
in place.
Waves – Mechanical & Electromagnetic
Node – The stationary point where two equal wave pulses meet and displacement
is zero.
Antinode – The point of largest amplitude.
Reflection – A change in the direction of a wave that is either inverted or
displaced in the same direction as the incident wave.
Refraction – A change in the direction of waves crossing a boundary between two
different media.
REFLECTION VS. REFRACTION
Diffraction – The bending of waves around a barrier.
DIFFRACTION EXAMPLE IN WATER:
Waves – Mechanical & Electromagnetic
BASICS OF SOUND:
Sound Waves – Sound is caused by pressing air molecules closer together. Sound
is a longitudinal wave. By pressing air molecules closer together, sound waves
cause pressure changes that the ear can detect and the brain can interpret as
sound.
Speed of Sound – Depends on the temperature of the air.
 343 m/s
 Can travel through air, liquid, solid
 Must have a medium (no sound in space, vacuum)
Loudness – Amplitude, measure of the variation in pressure along the wave.
 Measured on the sound level scale
Decibels – Unit of measure on the sound level scale
Pitch – how high or low a sound is, related to frequency
Waves – Mechanical & Electromagnetic
 Middle C has a 262 Hz
 http://onlinetonegenerator.com/
The Doppler Shift – A change in the sound frequency due to the relative motion of
either the source or the detector
 http://www.youtube.com/watch?v=eo_owZ2UK7E
Resonance, Harmonics, Fundamental Frequencies??
BASICS OF LIGHT:
What is light? - the range of frequencies of electromagnetic waves that
stimulates the retina of the human eye. (400 nm – 700 nm)
 Travels in a straight line
 Wavelength determines the color
 Some electromagnetic waves go undetected by the human retina
Speed of light – Is the same NO MATTER WHAT. It is the fastest speed in the
universe.
Waves – Mechanical & Electromagnetic
 3 x 10 8 m/s
Polarization – Light consisting of waves that vibrate on a specific plane. The
quality of having two opposite magnetic poles, one south-seeking and one northseeking.
Refraction – A change in the direction of waves crossing a boundary between two
different media.
REFRACTION EXAMPLE: