2.1 Waves Flashcards
What is the definition of wavelength?
The distance between 2 successive crests or troughs OR The distance a wave progresses in one period.
What is the definition of frequency?
Number of waves passing a point per second.
What is the definition of time period?
Time taken for one wave to pass a point.
What is the definition of phase?
Specifies the location or timing of a point within a wave cycle.
What is the definition of wavefront?
A line joining points of the same phase in a wave, eg crest.
What is the definition of amplitude?
Maximum displacement measured from equilibrium.
What is a progressive wave?
Waves that transport energy to the surrounding areas without transporting matter.
What do waves transport?
Waves transport energy but not matter.
What are examples of mechanical waves?
Mechanical waves require a medium to travel through, eg water and sound.
What are examples of electromagnetic waves?
Mechanical waves do not require a medium to travel through, eg radio waves, gamma waves and visible light.
What are the 2 types of progressive waves?
Transverse waves and longitudinal waves.
What is a transverse wave?
A wave where the vibrations are perpendicular to the direction of wave propagation.
What is a longitudinal wave?
A wave where the vibrations are parallel to the direction of wave propagation.
What are compressions and rarefractions?
Areas of zero displacement in longitudinal waves.
What are compressions?
High pressure areas of longitudinal waves.
What are rarefractions?
Low pressure areas of longitudinal waves.
What are the properties of electromagnetic waves?
- All travel at the speed of light.
- Can all travel through a vacuum (at the speed of light).
- Are all transverse waves.
What is polarisation?
Electromagnetic (EM) waves travel as oscillations in electric and magnetic fields and can transmit energy through a vacuum.
They are always transverse waves.
What is glare?
Glare is caused by unpolarised light.
What is a plane?
A flat surface on which a straight line connecting 2 points would lie. Examples of planes are the horizontal and vertical planes.
What is unpolarised light?
Unpolarised light has vibrations (perpendicular to the direction of travel) in many planes.
How can we polarise light?
Light can be polarised by passing the wave through a filter which limits the vibrations to one direction.
What is plane polarised light?
Plane polarised light has vibrations in a single plane which includes the direction of the wave propagation.
OR
Plane polarised light has vibrations in a single direction which is perpendicular to the direction of the wave propagation.
What happens when unpolarised light passes through a polaroid filter?
Approximately half of its energy is absorbed (intensity halves).
How can polarisation be used in industry?
A third polariser put between 2 perpendicular filters can let some light through. The middle filter rotates the direction of polarisation of light from the first filter so that some of it can now pass through the second one. This is used in visualising stress patterns in materials.
What does it mean when a wave is in phase?
- If two waves are described as being “in phase,” this means that corresponding points in each wave coincide in time.
- The distance between corresponding points along the direction of propagation is equal to an even number of half wavelengths.
What does it mean when a wave is in antiphase?
- If two waves are described as being in “antiphase,” this means that
- The distance between corresponding points along the direction of propagation is equal to an odd number of half wavelengths.
How do sunglasses polarise light?
- A large concentration of the vibrations are reflected in the plane which is parallel to the reflecting surface (typically in the horizontal plane).
- The extent to which polarisation occurs is dependent upon the angle at which the light approaches the surface and upon the material that the surface is made of.
