MCAT Study Guide Physics Ch. 10 – Sound Waves 2017-08-15T06:45:05+00:00

I.          10.1:  SOUND WAVES

A.     Longitudinal waves

Sound waves are different than mechanical waves; the particles oscillate in a direction parallel to the direction the waves travel (not 丄 to)

1.     Compressions – the regions of high pressure in sound waves

2.     Rarefactions – the regions of low pressure in sound wave

B.     Frequency – 20 Hz to 20 kHz

C.    Speed of sound in air – 340 m/s

 

II.          10.2:  STANDING SOUND WAVES IN TUBES

A.     This is analogous to standing mechanical waves in a rope

B.     Tube open at both ends

1.     Both ends are antinodes

a)     λn = 2L/n

b)     fn = nv/2L

c)     n is any positive integer

C.    Tubes closed at one end

1.     Both ends are nodes

a)     λn = 4L/n

b)     fn = nv/4L

c)     n is an odd number!

 

III.          10.3:  BEATS

A.     Beats

Sound waves of nearly equal frequency that interfere with each other

1.     Because frequencies don’t match, sometimes they are in phase and sometimes out of phase

2.     In phase = amplitudes add

3.     Out of phase = amplitudes subtract

B.     Beat frequency

Frequency at which the beats are heard equals the difference between the frequencies of the two original sound waves

1.     fbeat = |f1 = f2|

IV.          10.4:  INTENSITY AND INTENSITY LEVEL

A.     Intensity

Energy (power) transmitted per second per unit area (W/m2)

1.     I = power/area

2.     I is inversely ∝ to r2 (r = distance from source); area = πr2

B.     Threshold of hearing

Lowest intensity human ear can perceive, 10-12 W/m2, = I0

C.    Intensity level (sound level) – base 10 log of ratio I/I0, in β

1.     β = 10log10(I/I0)

a)     Every time we multiply I by 10, we add 10 to β

b)     Every time we divide I by 10, we subtract 10 from β

 

 V.          10.5:  THE DOPPLER EFFECT

A.     Doppler effect

Perceived frequency of sound is different than emitted sound due to the movement of a source (either towards or away from detector)

1.     fD = fS

[(v ± vD)/(v ∓ vS)]

a)     Remember, top sign is toward

(1)   If vD is moving toward source, use the + sign

(2)   If vS is moving toward the detector, use the – sign

b)     fD = frequency heard by the detector

c)     fS = frequency emitted by the source

d)     vD = speed at which the detector is moving

e)     vS = speed at which the source is moving

f)       v = speed of the wave (usually 340 m/s)

MCAT Study Guide Physics - Kim Matsumoto


More MCAT Study Guide Physics

1.

Ch. 2 Kinematics

2.

Ch. 3 Force

3.

Ch. 4 Center of Mass + Torque

4.

Ch. 5 Work, Power and Energy

5.

Ch. 6 Hydrodynamics

6.

Ch. 7 Electricity

7.

Ch. 8 Electrical Circuits

8.

Ch. 9 Simple Harmonic Motion

9.

Ch. 10 Sound Waves

10.

Ch. 11 Reflection + Refraction

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