4.4 Waves Flashcards
What is a progressive wave?
An oscillation that travels through matter (or in some cases a vacuum), transferring energy from one place to another, but not transferring any matter.
What is a transverse wave? Give an example.
A wave with oscillations that are perpendicular to the
direction of energy transfer.
For example, EM waves.
What is a longitudinal wave? Give an example.
A wave with oscillations that are parallel to the direction of energy transfer. They cannot travel through a vacuum.
For example, sound waves.
Define displacement.
The distance from the equilibrium position in a particular direction.
Define amplitude.
The maximum displacement from the origin.
Define wavelength.
The minimum distance between two adjacent points on a wave oscillating in phase.
Define period.
The time taken for a full oscillation of one wavelength to pass a given point
Define frequency.
The number of complete oscillations passing a given point per unit time.
How can we find the frequency of a wave?
Frequency (f) = 1 / Period (T)
What are two equations for finding wave speed?
Wave speed (v) = Wavelength (λ) / Period (T)
Wave speed (v) = Wavelength (λ) x Frequency (f)
Define reflection
When waves rebound from a barrier, changing direction but remaining in the same medium.
How does light reflecting off a mirror work?
The angle of the incident ray to the normal of the boundary between the two media is the same as the angle of the reflected ray to the normal.
How does wavelength and frequency change during reflection?
It doesn’t.
Define refraction.
When waves change direction when they travel from one medium to another due to a difference in the wave speed in each medium.
A wave has been refracted.
How has the frequency of the refracted wave changed in the new medium?
It is the same.
A wave has been refracted.
How has the speed of the refracted wave changed in the new medium?
It has changed, depending on the type of wave and the density of material.
Sound waves speed up in denser materials, whereas EM waves slow down.
The wavelength changes, as a result.
A sound wave is refracted in a dense material.
How has its speed changed?
It has sped up.
An EM wave is refracted in a dense material.
How has its speed changed?
It has slowed down.
In refraction, wave speed changes whereas frequency remains the same. How does this affect wavelength?
Wavelength also changes.
What will there always be in refraction?
Partial reflection at the boundary between the two media.
What is diffraction?
The spreading out of a wave front as it passes through a gap.
How is wavelength and frequency affected during diffraction?
They remain the same.
When will maximum diffraction occur?
When the gap the wave passes through is the same size as the wavelength of the incident wave.
Polarisation is a property unique to what kind of wave?
Transverse waves.
When does polarisation occur?
When the oscillation of a wave is restricted to one place only - this type of wave is said to be plane polarised.
Why can longitudinal waves not experience polarization?
The direction of energy transfer is already in one plane only.
Why can transverse waves experience polarization?
The oscillations occur in many planes, at right angles to the direction of travel.
