Wave Characteristics

Terms to Review Parts of a Wave – Crest – Trough – Pulse – Amplitude – Wavelength – Frequency – Period Types of Waves – Mechanical Waves – Electromagnetic Waves – Transverse Waves – Longitudinal Waves – Surface Waves

Calculations to Know Speed of wave (velocity) = freq x wavelength Frequency = cycles/second Period = seconds/cycle Frequency = 1/period Period = 1/frequency

Characteristics of Waves  Amplitude of a wave is its maximum displacement from the rest or equilibrium position.

Slinky Waves  Hand of one partner = vibrating source of energy  Slinky = material medium through which energy is transferred  Frequency of wave = number of complete cycles passing a given point in a unit of time (i.e. a second)  Frequency of wave is determined by the source (person)  Once a wave is produced, its frequency will never change (even if the speed and wavelength change)  As wave travels through the slinky, its amplitude usually decreases as some energy is lost to friction

Principle of Superposition  When two waves are travelling through a medium at same time (sent pulse from either direction)  Principle states that: displacement of a medium caused by two or more waves is the sum of the displacement caused by the individual waves  Result of superposition of two or more waves is called interference.

Types of Interference 1)Constructive Interference - two pulses travelling in the same direction - results in wave with a larger amplitude that any of the individual waves

Types of Interference 2) Destructive Interference - two pulses travelling in the opposite direction - results in a wave with a smaller amplitude

Wave Behaviour at Different Media  Speed of wave depends only on properties of the medium –Speed of water waves depends on depth of water –Speed of rope wave depends on force exerted on rope –Speed of sound wave depends on temperature of air  This means, for a given medium, –higher frequency = shorter wavelength –lower frequency = longer wavelength Speed of wave = frequency x wavelength

Speed of Slinky Waves  Speed of wave doesn’t depend on amplitude or frequency of the wave...it only depends on the properties of the medium.  For example, you can’t make a sound wave travel any faster by shouting quicker...the medium (air) is still the same.

Waves in Different Media  Design an experiment to test the speed of waves in different media  Prove that the speed of waves depends only on the media – a wave in the same media will always have the same speed  Hand in: 1)Question 2)Prediction 3)Materials 4)Procedure 5)Data/Observations 6)Conclusion

Wave Behaviour in Different Media  Waves typically move from one media to another (i.e. Light wave from air to water)  When a wave (incident wave) reaches a boundary of a medium, some of the wave energy continues into new medium (transmitted wave) and some of the wave energy is reflected back (reflected wave)  The wave that continues on (transmitted wave) will have the same frequency as the original wave (incident wave)

Wave Behaviour in Different Media  If the difference in media is small: –Amplitude of transmitted wave almost = incident wave –Amplitude of reflected wave = small –This means most energy is transmitted to new medium  If the difference in media is large: –Most of wave energy will be reflected –As a result, amplitude of the reflected wave will almost = amplitude of the incident wave

Wave Behaviour in Different Media  When wave passes from a less dense to a more dense medium (i.e. Slinky wave hitting a wall) –The reflected wave will be inverted  When a wave passes from a more dense media to a less dense medium (i.e. Slinky wave to air) –The reflected wave will be erect

Waves Speeds in Different Media  Wave from a light spring moving to a heavy spring: –Frequency of waves are the same (remember frequency only depends on the source producing the wave) –Speed of the wave in the heavier spring is slower –Using our equation (velocity = frequency x wavelength), less speed = smaller wavelength –If speed of wave increases in the new medium, wavelength will be larger

Standing Waves  When two pulses with equal, but opposite amplitude meet, one point in the medium will remain completely undisturbed –This point is called a node –At a node, the medium is never displaced –It is produced by destructive interference  When two pulses with equal amplitude in the same direction meet, one point in the medium undergoes the greatest displacement –This point is called an antinode –At an antinode, the medium has the greatest displacment –It is produced by constructive interference

Standing Waves  Standing waves are produced by identical waves travelling in opposite directions  The wave appears to be standing still  It has both nodes and antinodes

Complete Wave Ripple Tank Lab wave-interference Complete Wave Ripple Tank Lab wave-interference wave-interference wave-interference

Wave Reflection Law of Reflection: The angle of incidence is equal to the angle of reflection

Wave Refraction  Refraction = what happens when waves move from one medium to another (i.e. From shallow to deep water) –Shallow waves have shorter wavelength (since frequency stays the same, velocity must decrease)  When waves enter different media, the direction of the wave can change. This is known as refraction.

Wave Diffraction  When waves pass through small barrier, they bend around edges forming circular waves  Spreading of waves around the edge of a barrier is called diffraction

Wave Interference  When two waves pass through a barrier, both are diffracted (become circular waves) PLUS the two waves interfere with eachother  Interference produces regions of constructive and destructive interference –Constructive = two crests or two troughs meet –Destructive = a crest meets a trough

Water Interference  Constructive interference creates antinodes while destructive interference creates nodes  This pattern produces “antinodal lines”  Between antinodal lines are areas when crests meet troughs – these are nodal lines