Waves Flashcards
Wave Motion
Kind of disturbance which travels through a medium due to repeated vibrations of the particles of the medium about their mean positions
Propagation of Sound Waves through Air
- A small region in air is likes a spring - As it travell through the air, it compresses or expands it
- If a region is compressed, density increases of the second region causeing the first region density to decrease
- This causes rarefaction and hence shifts it to adjacent region
Propagation of sound in a solid
- When an eleastic wave propagates, the atom is displaced from its equilibrium position and a restoring force is developed
Transverse Waves
- Waves in which the individual particles of the medium oscillate perpendicular to the direction of wave propagation
- Travel through a liquid medium
Longitudinal Waves
- Waves in which the individual particles of the medium oscillate along the direction of wave propagation
- Travel through all media
Angular Frequency
Rate of change of phase with time
Wavelength
Distance covered by a wave during the time in which a particle of the medium completes one vibration to and fro about its mean position
Angular wave number / Propagation constant
Quantity 2pi / lambda (phase change per unit path difference)
Wave velocity / Phase velocity
Direction covered by a wave per unit time in its direction of propagation
Speed of transverse wave on stretched string
v = root (T / m)
Speed of a transverse wave in a solid
v = root (modulus of rigidity (aka shear modulus) / ro)
Speed of longitudinal Wave in a liquid or gas
v = root (k / ro)
k = bulk modulus
Speed of longitudinal wave in a solid
root (k + 4/3 * shear modulus) / ro)
Speed of a longitudinal wave in a solid rod
v = root (Y / ro)
Newton’s Formula for speed of sound in a gas
v = root (P / ro)
Laplace formula for speed of sound in a gas
v = root (gamma * P / ro)
gamma = Cp / Cv
Plane Progressive harmonic wave
If during the propagation of a wave through a medium, the particles of the medium vibrate simple harmonically about their mean positions, then the wave is said to be plane progressive
Factors which affect speed of sound in a gas
- Pressure has no effect!
- At constant pressure, v inversely proportional to square root of density
- Travels faster in moist air than dry hair
- Directly proportional to square root of abs. temp
Progressive Wave
Wave that travels from one point of the medium to another
Angular wave number or Propagation constant
k = 2pi / lambda
y(x,t) =
A sin (omega t - kx)
= A sin 2 pi(t / T - x / lambda)
= A sin 2pi/T (t - x / v) = A sin 2pi / lambda (vt - x)
Explain Progressive wave
y = A sin (omega t - kx + psi not)
y = Displacement
A = amplitude
omega = angular freq
t = time
k = angular wave number
x = position
psi not = initial phase angle