Acoustics and Optics Practice Exam Concepts

A set of 60 vocabulary-style flashcards covering physics principles of sound and light, including the Doppler effect, polarization, hearing thresholds, and electromagnetic energy, based on lecture notes and exam questions.

Ideal linear polarizer

A filter that allows only light waves with electric fields oriented parallel to its axis of polarization to pass through.

Axis of polarization

The specific orientation of an ideal linear polarizer that determines which electric field components of light are transmitted.

Unpolarized light intensity reduction

When unpolarized light passes through an ideal linear polarizer, its intensity is reduced by $50\%$ because waves with perpendicular electric fields are absorbed.

Wave period (Doppler effect)

The time interval of a wave cycle; it decreases when a source and observer move toward each other.

Refraction

The bending of light as it enters a new medium, which is not the primary cause of intensity loss in a linear polarizer.

Reflection

The bouncing of light off a surface; a portion of energy is reflected when sound moves from one medium to another.

Presbycusis

Age-related hearing loss that can be evaluated using an audiogram.

Pure tone

A sound characterized by a single sinusoidal waveform.

Audiogram

A plot of the relative intensity required for a given frequency to be detected by an individual.

Sound Intensity ($I$)

The amount of power (energy per unit time) delivered per unit area.

Decibel ($dB$)

A logarithmic unit used to express the ratio of the intensity of a sound to a reference level.

Decibel formula

The equation used to calculate sound level: $[dB] = 10 \log_{10} (\frac{I}{I_0})$

Perceived loudness

The human perception of sound intensity, which is approximately logarithmic.

$10\,dB$ increase

A change in sound level that corresponds to an intensity ratio increase by a factor of $10$.

$20\,dB$ increase

A change in sound level that corresponds to an intensity ratio increase by a factor of $10^2$, or $100$ times more intense.

$-30\,dB$ difference

A sound that is $30\,dB$ lower is calculated as $10^{-3} = \frac{1}{1,000}$ times less intense.

Noise-canceling earphones

Devices that use wave interference to reduce the intensity of ambient noise.

Wave interference

The phenomenon where two or more waves occupy the same space to create a single wave that is the sum of individual amplitudes.

Constructive interference

Occurs when the sum of two wave amplitudes results in a larger amplitude.

Destructive interference

Occurs when the sum of two wave amplitudes results in a smaller amplitude or zero displacement.

Phase shift for cancellation

A waveform shifted by half a wavelength relative to the original wave to achieve complete noise cancellation.

X-axis flip

A method to generate a waveform for complete noise cancellation by creating equal and opposite displacements.

Sound velocity in different media

Sound travels slowest in gases and fastest in solids.

Temperature effect on sound velocity

The wave velocity $v$ increases with temperature.

Tympanic membrane

A solid structure in the ear; when sound moves here from air, intensity decreases while velocity increases.

Hair cells

Sensory receptors lining the basilar membrane that detect fluid vibrations in the cochlea.

Cochlea

A fluid-filled spiral in the inner ear that acts as a resonator system.

Basilar membrane

A structure in the cochlear spiral where different sections are sensitive to specific frequencies.

Apex (Basilar membrane)

The part of the basilar membrane sensitive to low frequencies and low pitch.

Base (Basilar membrane)

The part of the basilar membrane sensitive to high frequencies and high pitch.

Low pitch

A sound characteristic associated with low-frequency waves and resonance at the apex of the basilar membrane.

Frequency-Wavelength relationship

The inverse relationship defined by the formula $c = f \lambda$ where $c$ is the speed of sound.

Wavelength ($\lambda$)

The distance between consecutive identical parts of a wave; for low frequencies, this value is relatively long.

Frequency ($f$)

The number of wave cycles per second, measured in Hertz ($Hz$).

Doppler effect

The change in observed frequency and wavelength due to the relative motion between a wave source and an observer.

Observed frequency (toward)

The frequency perceived by an observer when a sound source is moving toward them, which is higher than the emitted frequency.

Fundamental frequency formula (Open pipe)

The equation for the first harmonic in a pipe open at both ends: $f = \frac{v}{2L}$

L (Open pipe)

The length of the pipe; for a $0.25\,m$ pipe, the fundamental wavelength $\lambda$ is $2L = 0.5\,m$.

$700\,Hz$ resonance

Associated with a position approximately $25\,mm$ along the basilar membrane from the base.

Electromagnetic waves

Waves of energy that travel at $3.0 \times 10^8\,m/s$ in a vacuum.

Photon Energy ($E$)

The energy of an electromagnetic wave calculated by the formula $E = \frac{hc}{\lambda}$.

Planck's constant ($h$)

A physical constant used in the calculation of electromagnetic wave energy.

Speed of light ($c$)

The constant value of $3.0 \times 10^8\,m/s$ for electromagnetic waves in a vacuum.

Visible light spectrum

The portion of electromagnetic radiation between approximately $400\,nm$ and $750\,nm$.

High-energy light transitions

A progression from low to high energy corresponds to a transition from red to green to blue wavelengths.

Wavelength of red light

Visible light with a wavelength of approximately $750\,nm$, representing the lower energy end of the spectrum.

Wavelength of blue light

Visible light with a wavelength of approximately $400\,nm$, representing the higher energy end of the spectrum.

Increasing frequency

As the frequency of an electromagnetic wave increases, its energy also increases.

Laser Doppler vibrometer

A device that detects the Doppler shift of a laser beam to measure physical movement, such as chest displacement.

Displacement-time graph

A plot where the slope represents the instantaneous velocity of the object being measured.

Zero Doppler shift

Occurs when there is no relative motion (velocity is zero) between the wave source and the reflector.

Instantaneous velocity

Represented by the slope of the displacement-time graph; it determines the magnitude of the Doppler shift.

$$6 \times 10^{14}\,Hz$$

The frequency of a $500\,nm$ laser, calculated as $f = \frac{3.0 \times 10^8\,m/s}{500 \times 10^{-9}\,m}$.

Radio waves

Electromagnetic waves with the longest wavelengths and lowest energies.

Gamma rays

Electromagnetic waves with the shortest wavelengths and highest energies.

Infrared

Electromagnetic radiation with wavelengths slightly longer than visible red light.

Ultraviolet

Electromagnetic radiation with wavelengths slightly shorter than visible violet light.

Amplitude

The maximum displacement of a wave from its equilibrium position, related to sound intensity or perceived loudness.

Propagation velocity ($v$)

The product of wavelength $\lambda$ and frequency $f$, which remains constant for a wave in a specific medium.

Decreased observed frequency

Occurs when the source of a wave moves away from the observer.