Welcome to Physics 7C!. Lecture 2 -- Winter Quarter -- 2005 Professor Robin Erbacher 343 Phy/Geo firstname.lastname@example.org. Announcements. Course policy and regrade forms on the web: http://physics7.ucdavis.edu Quiz today! ~20 minutes long.
Lecture 2 -- Winter Quarter -- 2005
Professor Robin Erbacher
WavesSimple 1D Waves
What is a wave?
A wave is a type of internal motion of a medium, in which the displaced portion returns to equilibrium. This disturbance propagates in space as well.
Particles of the medium oscillate about their equilibrium positions in both a spatial and a temporal way.
What kind of waves are there?
propagates in x…Wave Parameters
Certain independent parameters characterize all waves:
Need y(x,t) !
2Snapshot v. Movie
Some waves are simply a pulse, and some are repetitive. These are harmonic (or sinusoidal), generated by SHOs.
Harmonic waves have a dependent
variable,wavelength , the distance
at which the oscillation repeats.
Movie:Go forward in time, see how spatial points move in SHM.
Snapshot:Hold time constant, see where we are in space.
solution is of the form:
Note: I swapped x and t term. Block notes differ from DL expression. Both ok. Use DL version
Too complicated? Think of the sin argument as one big phase (or angle) The Wave Representation
Describing the behavior of harmonic (sinusoidal) waves is extremely important in our physical world.
Because there is both a time-dependence and a translation of the wave in space, we need to represent the wave using both t andx.
What are all these parameters?
x: location in the medium (spatial)
t: time (temporal)
T,f, period, freq., wavelength
If we hold x constant, the wave will repeat in T seconds.
If we hold t constant, the wave will repeat in meters.
T and play similar roles in the wave function, determining
how often the wave will repeat in time and space.
Wave: a displacement in space and time. The angle, , found from (T, , x, t, ), determines the total displacement y(x,t).
So, the velocity of the wave, or propagating disturbance, can be found by riding along the wave at constant :
Particle moves as SHO!
Note: I swapped x and t term. Block notes differ from DL expression. Both ok. Use DL versionParticle Velocity
What is the velocity of a particle
(or length of string) on the wave?
Equilibrium = Atmospheric (or surrounding) pressureSound Waves
The sound vibrations in 1-Dimension, such as long, narrow tubes, trombone, flute, trumpet, follows harmonic oscillations.But how does one describe the vibrations of the air?
It’s all about pressure (density) fluctuations!
What kind of wave is a light wave?
It’s a transverse excitation, perpendicular to the direction of wave propagation.
What’s the medium that’s displaced as the wave propagates?
Light propagates via oscillating electric and magnetic fields
(more on this later in the course!)
What happens when there is more than one wave?
When two or more waves meet, they interfere with each other.
Combining waves by adding them is known as superposition.
Consider two waves on a string. What’s the maximum displacement of the string from equilibrium?
In Phase:1 - 2 = n2(n=integer)
Out of Phase:1 - 2 = [(2n-1)/2]2(n=integer)