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A light bulb is a source of a spherical wave. If you are 5 ft away from the bulb and walk another 5 ft away the light intensity decreases by a factor of 2 2 = 4. At the Earth surface the radius of curvature of the wave front is 150,000,000 km,
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A light bulb is a source of a spherical wave. If you are 5 ft away from the bulb and walk another 5 ft away the light intensity decreases by a factor of 22 = 4. At the Earth surface the radius of curvature of the wave front is 150,000,000 km, The intensity is the same everywhere, and the wave is practically flat. It is a spherical wave on the scale of the Solar system, though. In terms of intensity of sunlight, it is about the same as going from Venus to mars
If there are big waves and ripples on the water surface, which are going to run faster? For some kinds of waves the wave speed of a simple harmonic wave depends on the wave length. This phenomenon is called dispersion. Example – for large waves on the surface of deep water
Combining of two waves to form a composite wave is calledInterference
When two (or more) waves of the same kind propagate through the same region, they produce a composite wave. This phenomenon is called interference. It is constructive, when the waves reinforce each other. It is destructive, when they reduce each other’s amplitude. Usually the disturbances (displacements) the waves produce are added algebraically. This is called superposition principle.
Superposition of pulses: Destructive Interference For a moment it the string becomes a straight line – no disturbance is seen. Does the energy of wave motion disappear? Where does it go? How can the two waves go on after that? Two kinds of energy in the wave motion: potential – depends on deflection of the string from the straight line; kinetic – depends on velocity of motion of the string. In the very moment, when the string becomes straight, it is actually moving very fast - high K.
http://www.kettering.edu/~drussell/Demos/superposition/superposition.htmlhttp://www.kettering.edu/~drussell/Demos/superposition/superposition.html
When there are two interfering waves with close but different frequency the result of the interference is the beats. They are perceived as a wave with an average frequency, but with a slowly oscillating amplitude. http://www.kettering.edu/~drussell/Demos/superposition/superposition.html http://webphysics.ph.msstate.edu/jc/library/15-11/index.html
When there are two interfering waves with close but different frequency the result of the interference is the beats. They are perceived as a wave with an average frequency, but with a slowly oscillating amplitude. The resulting composite wave: http://webphysics.ph.msstate.edu/jc/library/15-11/index.html
When there are two interfering waves with close but different frequency the result of the interference are beats. They are perceived as a wave with an mean frequency, but with a slowly oscillating amplitude. slowly oscillating amplitude mean frequency
What about wave shapes?Are all periodic waves (not pulses) harmonic? Harmonic waves are simplest kind of waves. Other periodic waves (rectangular, triangular etc.) and even wave pulses can be represented as sums of harmonic waves with frequencies, which are multiples of the basic one (higher harmonics), and different amplitudes. Fourier decomposition.
A harmonic wave is the simplest kind of wave. Real waves may have ugly profiles. It is often convenient to present those complex waves as sums of simple harmonic waves with frequencies, which are multiples of the same basic frequency. Fourier decomposition. http://www.kettering.edu/~drussell/Demos/Fourier/Fourier.html
Limits of applicability of the superposition principle. Superposition principle suggests that disturbance of the composite wave is an algebraic sum of the disturbances produced by the individual waves. This is NOT true, when the amplitudes of the individual waves are so large that they change the properties of the medium through which they propagate.One can tell that the second wave propagates through a different medium due to the perturbation made by the first wave. The interference does not result in algebraic addition then. + As the amplitude grows, the string gets more stretched, the tension force increases and so does the wave speed. A wave with a higher amplitude goes faster!
Waves breaking at a sea shore… Waves break when their amplitude becomes comparable with the sea depth.Bigger waves break further away from the shore.
Two waves may interfere constructively and add algebraically far from the shore 1.The amplitude of the composite wave with the larger amplitude becomes comparable with the depth further away from the shore2-4. Therefore the composite wave would break soonerthan any of the two constituent waves.The breaking wave is not any more a sum of the two constituent waves – the superposition principle is violated, when the amplitude becomes large compared with the depth.
