Wave Properties: Frequency

• A wave is a propagating and oscillating deformation of a quanta or medium.
• Water waves are transverse waves propagating through water molecules.
• Sound waves are compressions propagating through air molecules.
• Electromagnetic waves like light are perpendicular transverse waves oscillating in electric and magnetic fields.
• Light can be seen as quanta or photons that oscillate while following straight paths.
• Waves can be described and measured using the characteristics of amplitude, frequency, wavelength, speed, and period.

Frequency of a Wave

• Frequency is the number of completed wave cycles in a given amount of time.
• High-frequency waves complete more cycles per second.
• Low-frequency waves complete fewer cycles per second.
• High-frequency photons have higher oscillation energies.
• Frequency for visible light waves is experienced as color.
• Frequency for sound waves is experienced as pitch.
• Higher wave frequency correlates with shorter wavelenghts.
• Lower wave frequency correlates with longer wavelenghts.
• A wave's speed is determined by multiplying its wavelength by its frequency.

Frequency, Wavelength and Energy Correlations

• High frequency correlates to short wavelength and high energy.
• Low frequency correlates to long wavelength and low energy.

How to Find the Frequency of a Wave

• The formula for finding frequency is the inverse between the number of waves and the unit of time: f= 1/T
• f represents frequency.
• T represents the unit of time.
• Frequency is measured in hertz (Hz).
• 1 Hz is equal to 1 wave per second.
• 1 Hz is equal to 60 revolutions per minute (60 rpm) or 60 waves per minute.

Period Vs Frequency

• The period is the amount of time it takes for a single wave cycle to complete.
• The period of a wave is also represented in the same frequency formula: Frequency = 1/period
• If a wave cycle has a period of 2.8 seconds, its frequency is 1/2.8 = 0.357 Hz.

Amplitude of a Wave

• Amplitude is the measurement for the distance between the medium at rest and its crest or trough
• Amplitude measures the amount of energy that is transported or carried by a single wave cycle.
• Higher amplitude means more energy is carried by the wave.
• Amplitude is represented by the symbol A.
• Transverse mechanical waves' amplitudes are expressed as a distance such as in units of meters.
• Longitudinal waves' amplitudes use units of pressure such as pascals (Pa).
• The intensity of a pressure wave compared to normal pressures can be measured as decibels (dB), which describe the energy carried by a wave in terms of loudness.
• Electromagnetic waves' amplitude can be described in volts per meter (v/m).
• Electromagnetic wave amplitudes can be described as brightness, intensity, or luminosity.

How to Measure Amplitude

• To measure the amplitude of a simple sine or transverse wave, measure the distance between a middle line cutting horizontally through the cycles of waves, and the crest or trough of the wave.
• To measure the energy carried by light or sound waves, special equipment is used to measure the intensity of pressure waves (pascals or decibels) or brightness/luminosity.

Amplitude Vs Frequency

• Amplitude is not correlated with frequency.
• Two sets of waves can have the same frequency but different amplitudes.
• With visible light, frequency describes the color, while amplitude describes the brightness.
• With sound waves, raising the volume increases the amplitude (loudness), but the pitch (frequency) remains the same.
• A high-pitch sound (frequency) can have the same output in decibels as a very low-pitch sound (frequency).