Characteristics of Waves Overview

How do waves and vibrations affect our lives? Earthquakes destroy or damage buildings cause land slides cause tidal waves Compressors May cause unwanted vibrations elsewhere in a building Strong Winds dangerous vibration in the structure of buildings Oscilloscopes used to learn how electronic components are performing

Mechanical Waves A mechanical wave is a wave that requires a medium – such as air, water, or steel – to transfer its energy from one location to another. Mechanical waves always occur in an “elastic” medium, the particles spring back to their original location after they are displaced. The molecules pass the disturbance along to their neighbors, from one molecule to the next. The matter in the medium doesn’t move along with the wave, only the energy.

Electromagnetic Waves Waves that don’t require a medium to transfer their energy from one place to another are electromagnetic waves. Electromagnetic waves can travel through a vacuum, like space, that contains no matter.

What are the Main Types of Waves? There are two main types of waves. Transverse Waves – propagate perpendicular to the direction the molecules vibrate Longitudinal waves – propagate parallel to the direction the molecules vibrate

What are the Characteristics that Describe Waves? Remember that a mechanical wave requires a medium – a vehicle to transport it. Electromagnetic waves don’t. The important characteristics that describe waves include: amplitude – Maximum distance that molecules move away from the neutral position wavelength – the distance between any pair of adjacent, in-phase, molecules frequency – the number of wavelengths that pass by any fixed position each second period – the number of seconds that each wave takes to pass by a fixed point speed – how fast a wave is moving away from the source

Continuous Waves A Continuous wave is created by repeated wave pulses, one after another. This is also called a periodic wave. A vibration or disturbance at some point in a medium is required to generate a wave. A single vibration or disturbance of the medium generates a single pulse. A repeated vibration or disturbance of the medium generates a train of pulses that form a continuous wave. A wave transports (moves or propagates) a disturbance (energy) from one place to another in a medium without causing a bulk movement of the medium.

What is a Harmonic Wave? A harmonic wave is a special type of continuous wave. It has two important characteristics: It’s formed, at some source, by a regular repeating vibration (like a cork bobbing up and down on a pond surface). Its shape is that of a very special, smooth wave called a sinusoidal (sine) wave that repeats itself over and over again.

How can we produce harmonic waves?

What’s wave amplitude? wave amplitude is the maximum distance of a particle from its neutral position. or: the distance of a crest above the neutral position, or a trough below the neutral position The wave amplitude is usually controlled by the vibrating source. The amplitude of a wave determines how much energy the wave carries.

What’s meant by wavelength? Wavelength is the length of the repeating shape or pattern of the wave. Designated by the Greek symbol, “λ” (lambda). Wavelength is the distance between a point on a wave and the same point on the next wave.

Example: Wave Amplitude and Wavelength Water waves pass by a 16-foot fishing boat. There are exactly 12 crests from front to back of the boat. A fisherman notices that the vertical distance between a crest and trough is about one-fourth as high as the boat. The boat is 28 inches high. Find the wave amplitude and the wavelength of the water waves. Make a drawing of the wave, labeling amplitude and wavelength.

What are wave frequency and wave period? Wave frequency is the number of complete waves that pass a point in the propagating medium each second. Wave period is the length of time it takes for a complete wave to pass a certain point. 𝑃𝑒𝑟𝑖𝑜𝑑= 1 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦= 1 𝑃𝑒𝑟𝑖𝑜𝑑 T = wave period in seconds f = wave frequency in waves/second, cycles/second, or hertz (Hz)

Example: Wave Frequency and Period The fisherman in the previous example notices that 3 wave crests pass him every 2 seconds. Find the wave frequency and the wave period.

Example: Frequency and period of a sine-wave trace on an oscilloscope The sine wave trace of a voltage signal on an oscilloscope is shown. The time/div setting is 0.05 sec. Find the frequency of the signal and the period of the signal.

What does phase difference mean? Phase is a way to compare two separate wave points on the same waveform. The difference between similar points on the waves is called the phase difference. Phase difference can be measured in fractions of a wavelength or cycle.

Example: Measuring Phase Difference Find the phase difference between the curves in pair 1 and pair 2.

How is speed measured? The wave speed of a traveling harmonic wave equals the product of wavelength times wave frequency. 𝑣=𝑓λ v = wave speed in units such as ft/sec or m/s λ = wavelength in units such as ft or m f = frequency in units of cycles/sec or Hz

Example: Characteristics of a Sine Wave Find the peak-to-peak voltage, signal amplitude, wave period, wave frequency, speed of the sound wave in air.

Example: Wavelength of a radiowave A local FM radio station broadcasts at a frequency of 98.5 megahertz. The speed of the radiowave is 3 x 108 m/s. Find the wavelength of the FM radio wave at this frequency.

What are characteristics of longitudinal waves? Longitudinal waves are mechanical waves where the vibrations of the molecules in the medium take place along the direction of propagation of the wave. Sound waves are an example of longitudinal waves that are propagated in the air. Compressions are regions where molecules are bunched together (high pressure). Rarefactions are regions where molecules are farther apart (low pressure).

Workplace applications of waves and vibrations Medical ultrasound CAT scans EEG and EKG Microwaves Communications Non-Medical Ultrasound Machinists Sonar production of alloys