Waves: Topic 4.2 Travelling Waves Flashcards
Define travelling waves and explain the definition
Oscillations that transfer energy from one place to another without transferring matter
Energy is transferred by the waves, but matter is not
The direction of the motion of the wave is the direction of the energy transfer
Travelling waves can be of two types:
Mechanical Waves, which propagate through a medium and cannot take place in a vacuum
Electromagnetic Waves, which can travel through a vacuum
What is the wave equation
The wave equation describes the relationship between the wave speed, the wavelength and the frequency of the wave
c = fλ
Where
c = wave speed in metres per second (m s−1)
f = frequency in hertz (Hz)
λ = wavelength in metres (m)
How do particles oscillate in mechanical waves?
In mechanical waves, particles oscillate about fixed points
Transverse waves are defined as follows:
A wave in which the particles oscillate perpendicular to the direction of motion and energy transfer
Transverse waves do not need particles to propagate, and so they can travel through a vacuum
Longitudinal waves are defined as follows and state whether medium is needed or not
A wave in which the particles oscillate parallel to the direction of motion and energy transfer
Longitudinal waves need particles to propagate, and so they cannot travel through a vacuum
How longitudinal waves propagate?
As a longitudinal wave propagates, areas of low and high pressure can be observed:
A rarefaction is an area of low pressure, with the particles being further apart from each other
A compression is an area of high pressure, with the particles being closer to each other
What is a displacement-distance graph
A displacement-distance graph is also known as a wave profile
It represents the displacement of many particles on the wave at a fixed instant in time (e.g. t = 0)
A displacement-distance graph directly provides:
The amplitude A of the wave
The wavelength λ of the wave
What does the displacement-distance graph for a transverse wave indicate about the particles?
In the displacement-distance graph of a transverse wave moving in the horizontal direction:
Particles with positive displacement are those moving up
Particles with negative displacement are those moving down
What does the displacement-distance graph for a longitudinal wave indicate about the particles?
In the displacement-distance graph of a longitudinal wave moving in the horizontal direction:
Particles with positive displacement are those moving to the right
Particles with negative displacement are those moving to the left
What is a displacement-time graph
A displacement-time graphs represents the variation of the displacement of one particle with time
A displacement-time graph directly provides:
The amplitude A of the wave
The period T of the wave
What is an electromagnetic wave
An electromagnetic wave is generated by the combined oscillation of an electric and a magnetic field
These fields oscillate perpendicular to each other and to the direction of motion of the wave (i.e. the direction in which energy is transferred)
Mention other 3 features of electromagnetic waves
Electromagnetic waves are transverse waves and, as such, they can travel through vacuum
Regardless of their frequency, all electromagnetic waves travel at the speed of light c = 3 × 108 m s–1 in vacuum
Electromagnetic waves form a continuous spectrum based on their frequency
What is the visible spectrum
Humans can only sense electromagnetic waves with wavelengths in the range 700 nm - 400 nm, which are the limits of the so-called visible spectrum
Electromagnetic waves with longer and shorter wavelengths are invisible to the human eye
Mention 4 characteristics of sound waves
Sound waves are longitudinal waves and, as such, require a medium in which to propagate
Sound waves are generated by oscillating sources, which produce a change in density of the surrounding medium
The sound wave then travels with a series of compressions and rarefactions
Sound waves form a continuous spectrum based on their frequency
