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# MCAT Physics Ch. 7

Term | Definition |
---|---|

Transverse Waves | Oscillations of wave particles perpendicular to the direction of wave propagation (ex: "The Wave", electromagnetic waves) |

Longitudinal Waves | Oscillations of wave particles parallel to the direction of wave propagation (ex: sound waves) |

Displacement (x) | How far a point of a wave is from the equilibrium position, expressed as a vector quantity. |

Amplitude (A) | Mag. of its maximal displacement |

Crest | Max. point of a wave (point of most positive displacement) |

Trough | Min. point of a wave (point of most negative displacement) |

Wavelength (lambda) | Distance between two crests or two troughs of a wave |

Frequency (f) | Number of cycles it makes per second. It is expressed in hertz (Hz) |

Angular Frequency (w) | Another way of expressing frequency, and is expressed in radians per second |

Period (T) | Number of seconds it takes to complete a cycle. It is the inverse of frequency. |

Interference Describes: | The ways in which waves interact in space to form a resultant wave. |

Constructive Interference | Occurs when waves are exactly in phase with each other. The amplitude of the resultant wave is equal to the sum of the amplitudes of the two interfering waves. |

Destructive Interference | Occurs when waves are exactly out of phase with each other. The amplitude of the resultant wave is equal to the difference in amplitude between two interfering waves. |

Partially Constructive And Partially Destructive Interference | Occur when two waves are not quite perfectly in or out of phase with each other. The displacement of the resultant wave is equal to the sum of the displacements of the two interfering waves. |

Traveling Waves | Have continuously shifting points of max. and min. displacement |

Standing Waves | Produced by the constructive and destructive interference of two waves of the same frequency traveling in opposite directions in the same space. |

Antinodes | Points of maximum oscillation |

Nodes | Points where there is no oscillation |

Resonance | Increase in amplitude that occurs when a periodic force is applied at the natural (resonant) frequency of an object. |

Damping | Decrease in amplitude caused by an applied or nonconservative force |

Sound | Produced by mechanical disturbance of a material that creates an oscillation of the molecules in the material. |

Rank Of Speed Of Sound Through Forms Of Matter (High To Low): | Solids, liquids, gases |

As Density Of A Medium Increases, Speed Of Sound: | Decreases |

Pitch Of A Sound Is Related To Its: | Frequency |

Doppler Effect | Shift in the perceived frequency of a sound compared to the actual frequency of the emitted sound when the source of the sound and its detector are moving relative to one another. |

Apparent Frequency Will Be (BLANK) Than Emitted Frequency When The Source And Detector Are Moving Toward Each Other | Higher |

When Source Is Moving At Or Above The Speed Of Sound: | Shock waves can form |

Sound Level | Loudness or volume of sound |

Intensity Of A Sound Is Related To: | A wave's amplitude |

Strings And Open Pipes Support: | Standing waves. The length of the string or pipe is equal to some multiple of half-wavelengths. |

Closed Pipes (At One End) | Support standing waves and the length of the pipe is equal to some odd multiple of quarter-wavelengths |

Sound Is Used Medically In: | Ultrasound machines for both imaging (diagnostic) and treatment (therapeutic) purposes. |

Eq. 7.1: Wave Speed | v = f*lambda |

Eq. 7.2: Period | T = 1 / f |

Eq. 7.3: Angular Frequency | w = 2*pi*f = 2pi / T |

Eq. 7.4: Speed Of Speed | v = sq.root (B/D) B = bulk modulus, measure of the medium's resistance to compression. D = density of the medium. |

Eq. 7.5: Doppler Effect | f^1 = f (V +- VD) / (V +- Vs). f1 = perceived frequency. f = actual emitted frequency. |

Eq. 7.6: Intensity | I = P / A. P = power. A = area. |

Eq. 7.7: Sound Level | Beta = 10 * log * (I / I0). I = intensity of the sound wave. I0 = threshold of hearing (1 x 10^-12 W / m^2). |

Eq. 7.8: Change In Sound Level | Betaf = Betai + 10*log(If / Ii). If = final intensity, Ii = initial intensity. |

Eq. 7.9: Wavelength Of A Standing Wave (Strings And Open Pipes) | Lambda = 2L / n. L = length of a string. n = positive nonzero integer called the harmonic (number of half-wavelengths supported by the string). |

Eq. 7.10: Frequency Of A Standing Wave (Strings And Open Pipes) | f = nv / 2L. v = wave speed. L = length of string. n = pos. nonzero integer called the harmonic |

Eq. 7.11: Wavelength Of A Standing Wave (Closed Pipes) | Lambda = 4L / n. n = pos. nonzero integer called the harmonic. |

Eq. 7.12: Frequency Of A Standing Wave (Closed Pipes) | f = n*v / 4L. n = pos. nonzero integer called the harmonic. v = wave speed. L = length of string. |