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Wave Properties
Inquiry Question: What are the properties of all waves and wave motion?
Wave Motion
- What is the role of the medium in the propagation of mechanical waves? โ Mechanical waves transfer energy from one place to another through the medium. โ The energy from the disturbance is transferred through the medium. โ The medium itself doesnโt move, but its particles oscillate.
- Explain the transfer of energy involved in the propagation of mechanical waves. โ The particles of the medium move about an average position (equilibrium), which transfers the energy from one place to another. โ When energy is transferred, a wave is formed and therefore propagated through a medium.
- What is the difference between transverse and longitudinal waves? โ In transverse waves, the particles within the medium vibrate up and down, perpendicular to the direction of motion of the wave energy. โ In a longitudinal wave, the particles within the medium vibrate backwards and forwards, parallel to the direction of motion of wave energy.
- What is the difference between mechanical and electromagnetic waves? โ Mechanical waves need a medium, so that its particles can vibrate to transfer energy and form a wave. โ Electromagnetic waves do not require a medium since they do not transfer energy through the vibration of particles. These waves are generated by the oscillations of electric and magnetic fields (which exist anywhere).
Graphs Displacement-Distance Graphs
note: this graph shows a โsnapshotโ of the whole wave at a particular point in time
โ Amplitude โ The distance between the middle of the wave (equilibrium) and either the crest or the trough of the wave.
โ Because a particle only moves up and down in a transverse wave, or side to side in a longitudinal wave, the total distance an individual particle travels in one cycle is twice the amplitude of the wave. โ Wavelength โ Distance between any two points successive points that are in phase. โ For example: between two crests or two troughs.
Displacement-Time Graphs
note: this graph shows an individual particle travelling โ Amplitude โ The distance between the middle of the wave (equilibrium) and either the crest or the trough of the wave. โ Period โ Distance between any two points successive points that are in phase. โ For example: between two crests or two troughs. โ Frequency โ The frequency is calculated by using the period found in the graph, and applying ๐ = (^1) ๐ก โ Velocity โ The velocity can be calculated by using the frequency calculated and the wavelength from the displacement-distance graph and applying ๐ฃ = ฮป๐
Refraction โ Refraction is the change in direction of a wave caused by a change in speed. โ A change in speed occurs when a wave passes through from one substance to another. โ When waves go from a high refractive index to a low refractive index, (i.e. when they speed up), the waves refract away from the normal. โ When waves go from a low refractive index to a high refractive index (i.e. when they slow down), the waves refract towards the normal.
Note: โ If velocity increases, wavelength increases โ If velocity decreases, wavelength decreases โ Frequency is always constant โ There is still the same number of waves, waves cannot be gained or lost
Diffraction โ Diffraction is when waves bend as they travel around obstacles. โ If the slit is larger than the wavelength - minimal diffraction occurs โ If the slit is similar to or smaller than the wavelength - significant diffraction occurs
Wave Superposition โ Wave superposition occurs when two wave pulses approach each other and interact to cause a new wave. โ The new wave is made by adding the amplitudes of the two waves when the crests meet. โ This new wave is the consequence of the principle of superposition. โ Principle of Superposition: when two or more waves interact, the resultant displacement or pressure at each point along the wave is the vector sum of the displacements or pressures of the component waves. โ Constructive Superposition โ When two waves collide and are added together to create a larger wave and then just move on after the interaction. โ Destructive Superposition โ When two waves collide and create a smaller wave because the resulting wave is meant to be the vector sum of the two individual displacements.
Standing Waves โ Standing waves can be formed when two waves are being superpositioned, travelling in opposite directions. โ The reason it travels in opposite directions has to do with the fact that the waves are being reflected from a fixed end, causing them to invert and interfere with the new waves travelling down the rope. โ The two opposing waves need the same: โ Wavelength โ Frequency โ Velocity/Speed โ Amplitude โ This makes the wave look as if it is not travelling, and only oscillating up and down, hence the name โstanding waveโ. โ Progressive vs. Standing Wave: โ Progressive Waves โ Carry energy from one point to another through a medium โ They have a clear direction of propagation (moving from the source to other parts of the medium) โ Standing Waves: โ Donโt travel or propagate
โ 1 closed end and 1 open end for a standing wave
Resonance Natural Frequency โ The frequency at which all objects vibrate at or oscillate in the absence of disturbance. Driving Frequency โ The frequency applied to a mechanical system from an external source. Amplitude โ Amplitude refers to the maximum displacement from a system's equilibrium position. โ In resonance, when the natural frequency matches the driving frequency, the mechanical systemโs amplitude reaches its maximum because itโs absorbing energy from the external force with utmost efficiency. โ Basically, the amplitude of oscillation increases. Energy Transfer and Transformation โ Energy transfer always occurs if resonance is taking place. โ The energy from the object providing the driving frequency will transfer energy to the object that is oscillating at a natural frequency. โ There are two types of storage modes for these energies; kinetic and potential energy. โ When the system is at maximum amplitude, it holds maximum potential energy. โ As it goes towards its equilibrium point, the potential energy transforms into kinetic energy. โ The further it moves away from its equilibrium point: โ Kinetic energy decreases โ Potential energy increases โ This energy transformation is most efficient during resonance, hence the increased amplitude during resonance.
Sound Waves
Inquiry Question: What evidence suggests that sound is a mechanical wave.
Pitch โ The pitch of a sound is determined by the frequency of the sound waves. โ A high frequency is seen as a high pitch โ A low frequency is seen as a low pitch โ The reason why humans perceive a change in frequency as a change in pitch is because the longitudinal sound wave creates high and low pressure disturbances of the particles of the air which is detectable by the human ear.
Loudness โ The volume of the sound is determined by the amplitude of the sound wave. โ Large amplitude = sound being loud โ Small amplitude = sound being quiet โ It is also based on how you perceive the energy of a sound wave (basically the amplitude).
Longitudinal Wave โ The particles in a sound wave move parallel to the direction of wave propagation. โ This leads to areas of compression and rarefaction. โ Compression โ High air pressure โ Regions where the particles are close together โ Rarefaction โ Low air pressure โ Regions where particles are further apart โ Sound cannot travel through a vacuum and needs a medium because sound waves transfer energy through the vibration of particles.
Beats โ In sound waves, superposition creates louder sounds when constructive interference occurs and sister sounds when destructive interference occurs. โ The beat phenomenon occurs when two sound waves have the same amplitude but have slightly different frequencies. โ The interference between the two waves results in alternating constructive and destructive interferences. โ Results in a pulse-like sound called a beat. โ The beat frequency is the difference between the two wave frequencies. โ The frequency of the actual sound wave producing those beats is determined by finding the average of the two wave frequencies.
Doppler Effect โ The apparent change in frequency of a wave when either the observer or the source of the wave is moving. โ When the source of a wave is moving towards the observer, the waves get "compressed", leading to a higher frequency (shorter wavelength). โ When the source is moving away from the observer, the waves get "stretched", resulting in a lower frequency (longer wavelength).
Thermodynamics
- Inverse square law
- Lenses
- mirrors
