Waves and sound
53 flashcards covering Waves and sound for the ACT Science section.
Waves and sound are fundamental concepts in physics that describe how energy moves through space. A wave is essentially a disturbance that travels, carrying energy from one place to another without permanently moving the medium it's traveling through—like ripples on a pond or light from the sun. Sound, specifically, is a type of mechanical wave created by vibrations, such as when your vocal cords shake the air, allowing us to hear everything from music to speech. Understanding these ideas helps explain everyday phenomena and is crucial for grasping broader scientific principles.
On the ACT Science section, waves and sound often appear in questions that require interpreting graphs, analyzing data from experiments, or applying formulas like the wave speed equation (speed = frequency × wavelength). Common traps include confusing similar terms, like amplitude and frequency, or overlooking details in diagrams that show wave interference. Focus on practicing how to extract information from passages and identify relationships between variables, as these questions test your ability to think critically about real-world applications. Always double-check your units when performing calculations.
Terms (53)
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Wave
A wave is a disturbance that transfers energy through a medium or space without transferring matter.
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Amplitude
Amplitude is the maximum displacement of particles in a wave from their rest position, which determines the wave's energy.
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Wavelength
Wavelength is the distance between two consecutive points in phase on a wave, such as from crest to crest, and is typically measured in meters.
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Frequency
Frequency is the number of waves that pass a given point per second, measured in hertz, and it determines the pitch of sound waves.
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Period
Period is the time it takes for one complete wave cycle to pass a given point, measured in seconds, and is the inverse of frequency.
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Transverse wave
A transverse wave is one where the particles of the medium vibrate perpendicular to the direction of wave propagation, like waves on a string.
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Longitudinal wave
A longitudinal wave is one where the particles of the medium vibrate parallel to the direction of wave propagation, such as sound waves in air.
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Crest of a wave
The crest is the highest point on a transverse wave, representing the peak of the wave's oscillation.
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Trough of a wave
The trough is the lowest point on a transverse wave, representing the bottom of the wave's oscillation.
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Wave speed
Wave speed is the rate at which a wave travels through a medium, depending on the medium's properties and the wave's frequency and wavelength.
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Formula: v = fλ
The formula v = fλ calculates wave speed as the product of frequency and wavelength, where v is speed, f is frequency, and λ is wavelength.
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Sound wave
A sound wave is a longitudinal wave that travels through a medium by compressing and rarefying particles, allowing us to hear sounds.
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Pitch of sound
Pitch is the perception of a sound's frequency, with higher frequencies corresponding to higher pitches and lower frequencies to lower pitches.
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Loudness of sound
Loudness is the human perception of a sound's intensity, which relates to the amplitude of the sound wave and is measured in decibels.
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Decibel scale
The decibel scale is a logarithmic measure of sound intensity relative to the threshold of hearing, used to quantify loudness on a scale from 0 dB upward.
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Doppler effect
The Doppler effect is the change in frequency of a wave relative to an observer moving towards or away from the wave source, such as a siren sounding higher pitched when approaching.
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Reflection of waves
Reflection occurs when waves bounce off a barrier or surface, following the law of reflection where the angle of incidence equals the angle of reflection.
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Refraction of waves
Refraction is the bending of waves as they pass from one medium to another at an angle, due to a change in wave speed caused by the medium's density.
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Diffraction
Diffraction is the bending of waves around obstacles or through openings, allowing waves to spread out and interfere with each other.
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Interference of waves
Interference is the interaction of two or more waves that overlap, resulting in regions of increased or decreased amplitude depending on their phase.
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Constructive interference
Constructive interference happens when two waves with the same phase meet, adding their amplitudes to create a wave with larger amplitude.
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Destructive interference
Destructive interference occurs when two waves with opposite phases meet, canceling each other out and resulting in a wave with reduced or zero amplitude.
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Standing wave
A standing wave is a wave that appears stationary due to interference between incoming and reflected waves, with nodes and antinodes at fixed positions.
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Node
A node is a point on a standing wave where the amplitude is always zero, meaning the medium does not move at that location.
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Antinode
An antinode is a point on a standing wave where the amplitude is maximum, representing the peaks of vibration in the medium.
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Resonance
Resonance is the amplification of wave amplitude when an object's natural frequency matches the frequency of an external vibrating source.
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Natural frequency
Natural frequency is the frequency at which an object naturally vibrates when disturbed, depending on its physical properties like mass and stiffness.
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Speed of sound in air
The speed of sound in air is approximately 343 meters per second at room temperature, varying with temperature, humidity, and altitude.
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Factors affecting speed of sound
The speed of sound in a medium is affected by the medium's density and elasticity, increasing in warmer air and denser materials like solids.
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Echo
An echo is the reflection of sound waves off a surface, heard as a repeated sound after a short delay, useful for measuring distances.
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Reverberation
Reverberation is the persistence of sound in a space after the original sound stops, due to multiple reflections, which can affect sound clarity.
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Beats
Beats are the periodic variations in volume heard when two sound waves of slightly different frequencies interfere, used to tune musical instruments.
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Ultrasound
Ultrasound refers to sound waves with frequencies above the human hearing range, typically above 20,000 Hz, used in medical imaging.
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Infrasound
Infrasound consists of sound waves with frequencies below the human hearing range, typically below 20 Hz, often produced by natural events like earthquakes.
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Common trap: Confusing frequency and period
Frequency and period are inversely related, so increasing frequency decreases period, and students often mix them up in calculations.
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Common trap: Amplitude and energy
Larger amplitude means greater energy in a wave, but students might incorrectly assume amplitude affects speed or frequency.
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Wavelength and medium
Wavelength changes with the medium because wave speed varies, even if frequency remains constant, leading to shorter wavelengths in denser media.
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Inverse relationship of frequency and period
Frequency and period have an inverse relationship, expressed as T = 1/f, where T is period and f is frequency.
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Sound intensity
Sound intensity is the power per unit area of a sound wave, related to amplitude and distance from the source, measured in watts per square meter.
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Threshold of hearing
The threshold of hearing is the minimum sound intensity detectable by the human ear, about 10^-12 watts per square meter at 1,000 Hz.
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Sonic boom
A sonic boom is the loud noise produced when an object travels faster than the speed of sound, creating a shock wave that compresses air.
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Mach number
Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium, with values above 1 indicating supersonic speed.
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Supersonic speed
Supersonic speed is when an object travels faster than the speed of sound, creating a cone-shaped shock wave that affects surrounding pressure.
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Subsonic speed
Subsonic speed is when an object travels slower than the speed of sound, producing normal sound waves without a shock front.
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Example: Calculating wave speed
To calculate wave speed, use v = fλ; for instance, if frequency is 50 Hz and wavelength is 2 meters, speed is 100 meters per second.
A wave with 50 cycles per second and 2-meter wavelength travels at 100 m/s.
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Example: Doppler effect scenario
In a Doppler effect scenario, if a car horn approaches at 20 m/s with a frequency of 500 Hz and sound speed of 340 m/s, the observed frequency increases.
The observed frequency would be about 529 Hz for an approaching car.
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Wavefront
A wavefront is an imaginary line or surface representing points of a wave that are in the same phase, helping visualize wave propagation.
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Ray diagram for waves
A ray diagram for waves uses straight lines to represent the direction of wave travel, simplifying the study of reflection and refraction.
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Periodic wave
A periodic wave repeats its pattern at regular intervals, characterized by constant frequency and wavelength over time.
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Wave pulse
A wave pulse is a single, non-repeating disturbance that travels through a medium, unlike a continuous periodic wave.
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Frequency unit: Hertz
Hertz is the unit of frequency, representing one cycle per second, commonly used in wave and sound calculations.
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Common trap: Frequency and wavelength relationship
In a given medium, frequency and wavelength are inversely related through wave speed, so changes in one affect the other if speed is constant.
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Example: Wave on a string
For a wave on a string, increasing tension increases wave speed, as speed depends on the square root of tension divided by linear density.
A string with higher tension allows waves to travel faster than one with lower tension.