Making Waves
Objectives To investigate the basic nature of waves and their properties. Wave Properties: Speed, Wavelength, Frequency, and Period. Wave Phenomena: Reflection, Interference, and Transmission. Epic wave video
Ocean Waves A wave is a traveling disturbance. A wave carries energy from place to place without any transfer of matter.
Some waves such as mechanical waves (eg sound waves) require a medium in which to travel. Electromagnetic waves (eg. Light) are able to travel through a vacuum ie they do not require a medium.
A pulse is a single wave of short duration. Most waves repeat the same motion in a regular pattern – they are periodic.
Types of waves
Transverse waves A transverse wave is one in which the disturbance is perpendicular to the direction of travel (propagation) of the wave. Examples: Light wave, waves on a guitar string.
Longitudinal Waves Longitudinal wave is one in which the disturbance is parallel to the line of travel (propagation) of the wave. Example: Sound wave in air is a longitudinal wave.
State 2 differences between sound and light waves
1. Sound is longitudinal, light is transverse 2. Sound requires a medium
Seismic Waves Wave Type Motion of particles Velocity Other characteristics Longitudinal (P) Same as direction of propagation Faster ~6Km/s Travel through liquids Transverse (S) Perpendicular to direction of propagation Slower ~3Km/s Do not travel through liquids
What is a periodic wave? Periodic waves are waves that repeat.
Amplitude, Wavelength, and Period The amplitude, A is the maximum disturbance. The wavelength, λ is the horizontal length of one cycle of the wave .eg. The distance between two crests. The period, T is the time required for one complete up/down cycle of the wave. The Wave velocity, v is the velocity of the wave shape.
Frequency The frequency, f is the number of waves passing any point each second. The frequency is measured in hertz (Hz) Link
Wave Speed
Example Sound travels at 330 m/s in air. What will be the wavelength of a note with frequency 110 Hz?
Waves on a Rope
Pulses reflecting and transmitting Link
Superposition Link When 2 waves meet they can interfere with one another. 2 peaks or troughs coinciding form a wave twice as large – constructive interference. A peak and trough coinciding can “cancel” each other – destructive interference. Another link
Standing waves If two waves of the same amplitude, frequency and speed are produced from the ends of a hollow pipe or string then a standing wave forms.
Nodes and antinodes Where two wave peaks meet, a maximum displacement – antinode – forms. Peak and trough “cancel out” to form node.
Diffraction Link As a wave passes an object diffraction occurs – the wave bends. Longer the wavelength the greater the diffraction.(Sound more than light) A gap between two obstacles the same size as the wavelength gives maximum effect.
Interference
Periodic Wave
Harmonic Wave
The Speed of Wave on a String
Guitar The strings on a steel-string guitar have different weights, µ = m/L.
Q13
Principle of Superposition When two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves.
Constructive Interference of Sound Waves
Destructive Interference
Standing Waves
Nodes and Antinodes
What determines the frequency of a wave on a guitar string?
Making music with soft-drink bottles
Longitudinal Standing Waves Musical instruments in the wind family depend on longitudinal standing waves in producing sound. Since wind instruments (trumpet, flute, clarinet, pipe organ, etc.) are modified tubes or columns of air, it is useful to examine the standing waves that can be set up in such tubes.
Standing-Wave Patterns
Doppler Effect
Doppler Effect