Physics Unit 4: Waves Flashcards Preview

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Flashcards in Physics Unit 4: Waves Deck (15):
1

Types of Mechanical Waves

Mechanical Wave: the TRANSFER of ENERGY through a material due to vibration

1) Transverse Waves: a wave in which particles in the medium oscillate perpendicular to the direction of the flow of energy (aka energy propagation)
ex: particle is oscillating up and down while the wave motion is moving horizontally
- Do not occur in liquids of gases (light waves are an exception)

2) Longitudinal wave: a wave in which particles oscillate in the same direction as the flow of energy/energy propagation
ex: slinky, sound
-compression, rarefaction
^refer to the local pressure differences as the wave’s energy passes through the medium

2

Compression

Compression: the region in a longitudinal wave in which the medium’s particles are CLOSE together →maximum density/high pressure

3

Rarefaction

Rarefaction: the region in a longitudinal wave in which the medium’s particles are farther apart →minimum density/low pressure

4

Transverse Wave characteristics

• Amplitude: the maximum displacement of a wave/vibrating particle from its equilibrium point (halfway between the max and the min) →metres (transverse wave)
• Crest: Maximum point of a transverse wave
• Trough: Minimum point of a transverse wave

Wavelength: the distance BETWEEN two similar points in successive identical cycles in a wave, such as from a crest to crest or trough to trough (similar to period but in meters) →lambda
-distance of one complete cycle

5

Phase

Phase: in a continuous transverse or longitudinal wave, the x-coordinate of a unique point of the wave (same units as the wavelength→m)

Phase shift: a shift of an entire wave along the x-axis with respect to an otherwise identical wave (m)
- the amount that one waveform is displaced along the axis from an otherwise identical waveform -->transformations
-determine how much the wave has transformed (using wavelength)

ex: left a quarter of a wavelength = - lambda/4
Left = -
Right = +

In phase: the state of two identical waves that have the same phase shift (shown as one)

Out of phase: the state of two identical waves that have different phase shifts (the amount they are out of phase is equal to the phase shift)

6

Wave speed

Wave speed (v): the rate at which a wave/energy is travelling through a medium; also a measure of how fast the energy in the wave is moving →m/s

v = Wavelength/period = length of one cycle/time for one cycle

v = f*wavelength (in m/s)

Speed of a wave along a string:
v = Square root (Force of tension/linear density)

7

Frequency

Frequency (f): the number of complete cycles/waves that pass a point per unit time OR number of oscillations (up/down) per second, usually 1 s; measured in hertz (Hz)

Frequency = cycles/unit of time → f = 1/T

*short wavelength, high frequency
*long wavelength, low frequency

8

Period

Period (T): the time for a vibrating particle to complete one cycle (time for one oscillation)

Period = time/unit cycle → T = 1/f

9

Longitudinal wave characteristics*

• Amplitude: the maximum pressure it creates compared to the pressure of the non-disturbed medium
-->how far the slinky moves from its equilibrium point

Displacement-position graph: comparing the position to its equilibrium position
-if move to the left = going down/-
-if move to the right = going up/+

10

Factors affecting wave speed

Efficient transfer = faster wave
• Rigid medium
• Tighter medium (string)
• Lighter medium (the linear density (mu) in a string (mass))
• High temperature

11

Linear Density (mu)

• Linear density (mu): the mass per unit distance of a string; units are kilograms per meter (kg/m)

o Mu = m/L
(L is the length in meters)
(m = mass in kg)

12

Waveform

• Waveform: the shape of a wave when graphed

13

Displacement-time

Shows the displacement of a point as a function of time (point moves up then back down)
-can use displacement position graph and make displacement time graph by looking at what is happening next on the RIGHT

14

Displacement-position

Snapshot of the wave at a particular point in time

-predicting what is going to happen next by looking behind the y axis/LEFT (moving down or up)

15

Energy and amplitude

more energy = more work done on the slinky = more displacement = greater amplitude

*energy does not affect wavelength, frequency, and thus wave speed

Wavelength and frequency of a wave do not affect wave speed either

*Wave speed depends on the medium through which the wave travels