Physics Lect 6
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Wave formulas relating frequency and wavelength
- v = f λ
- velocity = (frequency)(wavelength)
- use only to find frequency or wavelength, velocity is independent of these two
the # of waves that pass a fixed point per second
- the # of seconds it takes for a complete wavelength to pass a fixed point
- T = 1 / f
What factors affect the speed of a wave
- Only medium affects the velocity of a wave
- (1) its elasticity (resistance to change in shape) - stores U - greater eleasticity speeds waves up
- (2) its inertia (resistance to change in motion) - stores K.E. - greater inertia slows waves down
Generally, stiff mediums ___ ___ waves.
Generally, heavy mediums ___ ___ waves.
What effect does temperature have waves traveling through a gas?
It increases velocity as it increases (more K.E.)
Velocity relates to what for surface waves?
with surface waves, velocity increases with depth
What is the elastic component of surface waves?
How is power measured?
- Power is measured in terms of intensity (I)
- I is proportional to A2 and f2 for all waves
- It is related to itself - dB (decibles)
- ~ however many zeros you add to an intensity - take that integer and add a zero behind it, this will give you the decible jump
- occurs when two waves with slightly different frequencies interfere with eachother
- at some points there are "in phase" (constructive) and sometimes they are out of phase (destructive)
- fbeat = | f1 - f2 |
- For sound waves, pitch correlates with frequency
- A high note will have a high pitch and a high frequency
What happens to waves at an interface of media?
- (1) some (or all) of the energy is REFLECTED
- if it is reflected off of a more dense medium than the medium it is coming from --> the wave is inverted (180° phase shift)
- if it is reflected off a less dense medium --> the wave reflects back upright (no phase shift)
- (2) the remaining energy is REFRACTED into the new medium
- these waves will have the SAME frequency, a DIFFERENT wavelength, and a SMALLER amplitude
- waves that contain nodes and antinodes
- node is "still" when observed
- antinodes have the greatest displacement from zero
- a list of wavelengths that create standing waves for a specific length of "string"
- listed from largest to smallest
- ∴ 1st has the longest λ and the fewest nodes (2)
- if both ends are secure:
- L = nλn / 2 (n = 1, 2, 3...)
- if one end is loose:
- L = nλn / 4 (n = 1, 3, 5...)
Simple Harmonic Motion
- motion that demonstrates a sine function of time
- objects in simple harmonic motion share certain properties: 1) acceleration is ∝ displacement but opposite in sign; 2) a & d are related by f2; 3) oscillates between kinetic and potential E
The Doppler Effect
when a source moves relative to the observer it can change the frequency and the wavelength of the wave that reaches the observer
Doppler Effect Formulas
- Δf / fs = v / c
- Δλ / λs = v / c
- fs: frequency produced by the source
- λs: wavelength produced by the source
- v: the net speed of the source and the object (if they are moving in the same direction you subtract their velocities; if they are moving in opposite directions you add their velocities)
With the Doppler Effect, what happens as the source and the observer grow closer?
The frequency increases and the wavelength decreases
What experiences no Doppler Effect?
- Objects moving in the same direction at the same speed
- v = 0 (because if they are moving in the same direction we subtract their speeds)
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