File Name: mechanical and electromagnetic waves .zip
Categories of Waves
Named after esteemed physicist James Clerk Maxwell, the equations describe the creation and propagation of electric and magnetic fields. Fundamentally, they describe how electric charges and currents create electric and magnetic fields, and how they affect each other. Magnetic field lines form loops such that all field lines that go into an object leave it at some point.
Thus, the total magnetic flux through a surface surrounding a magnetic dipole is always zero. Field lines caused by a magnetic dipole : The field lines created by this magnetic dipole either form loops or extend infinitely. The principle behind this phenomenon is used in many electric generators. Both macroscopic and microscopic differential equations are the same, relating electric field E to the time-partial derivative of magnetic field B :.
Maxwell added a second source of magnetic fields in his correction: a changing electric field or flux , which would induce a magnetic field even in the absence of an electrical current.
Electromagnetic Waves : Electric red and magnetic blue waves propagate in phase sinusoidally, and perpendicularly to one another. Electromagnetic waves are the combination of electric and magnetic field waves produced by moving charges.
Electromagnetic radiation, is a form of energy emitted by moving charged particles. As it travels through space it behaves like a wave, and has an oscillating electric field component and an oscillating magnetic field. These waves oscillate perpendicularly to and in phase with one another. Electromagnetic Wave : Electromagnetic waves are a self-propagating transverse wave of oscillating electric and magnetic fields.
The direction of the electric field is indicated in blue, the magnetic field in red, and the wave propagates in the positive x-direction. Notice that the electric and magnetic field waves are in phase. The creation of all electromagnetic waves begins with a charged particle.
This charged particle creates an electric field which can exert a force on other nearby charged particles. Once in motion, the electric and magnetic fields created by a charged particle are self-perpetuating—time-dependent changes in one field electric or magnetic produce the other. This means that an electric field that oscillates as a function of time will produce a magnetic field, and a magnetic field that changes as a function of time will produce an electric field.
Both electric and magnetic fields in an electromagnetic wave will fluctuate in time, one causing the other to change. Electromagnetic waves are ubiquitous in nature i. These and many more such devices use electromagnetic waves to transmit data and signals. All the above sources of electromagnetic waves use the simple principle of moving charge, which can be easily modeled. Placing a coin in contact with both terminals of a 9-volt battery produces electromagnetic waves that can be detected by bringing the antenna of a radio tuned to a static-producing station within a few inches of the point of contact.
Electromagnetic waves have energy and momentum that are both associated with their wavelength and frequency. Electromagnetic radiation can essentially be described as photon streams. These photons are strictly defined as massless, but have both energy and surprisingly, given their lack of mass, momentum, which can be calculated from their wave properties. Waves were poorly understood until the s, when Max Planck and Albert Einstein developed modern corrections to classical theory.
In other words, there were only certain energies an electromagnetic wave could have. Momentum is classically defined as the product of mass and velocity and thus would intuitively seem irrelevant to a discussion of electromagnetic radiation, which is both massless and composed of waves. However, Einstein proved that light can act as particles in some circumstances, and that a wave-particle duality exists.
And indeed, Einstein proved that the momentum p of a photon is the ratio of its energy to the speed of light. The speed of light in a vacuum is one of the most fundamental constant in physics, playing a pivotal role in modern physics. The speed of light is generally a point of comparison to express that something is fast.
But what exactly is the speed of light? Light Going from Earth to the Moon : A beam of light is depicted travelling between the Earth and the Moon in the time it takes a light pulse to move between them: 1.
The relative sizes and separation of the Earth—Moon system are shown to scale. It is just that: the speed of a photon or light particle.
The speed of light in a vacuum commonly written as c is ,, meters per second. This is a universal physical constant used in many areas of physics. For example, you might be familiar with the equation:. This is known as the mass-energy equivalence, and it uses the speed of light to interrelate space and time. This not only explains the energy a body of mass contains, but also explains the hindrance mass has on speed. There are many uses for the speed of light in a vacuum, such as in special relativity, which says that c is the natural speed limit and nothing can move faster than it.
However, we know from our understanding of physics and previous atoms that the speed at which something travels also depends on the medium through which it is traveling. The speed at which light propagates through transparent materials air, glass, etc. The refractive index of air is about 1. As mentioned earlier, the speed of light usually of light in a vacuum is used in many areas of physics. Below is an example of an application of the constant c.
Fast-moving objects exhibit some properties that are counterintuitive from the perspective of classical mechanics. For example, length contracts and time dilates runs slower for objects in motion. The effects are typically minute, but are noticeable at sufficiently high speeds. Typically, this periodic event is a wave. Most people have experienced the Doppler effect in action. Consider an emergency vehicle in motion, sounding its siren.
As it approaches an observer, the pitch of the sound its frequency sounds higher than it actually is. When the vehicle reaches the observer, the pitch is perceived as it actually is. When the vehicle continues away from the observer, the pitch is perceived as lower than it actually is. From the perspective of an observer inside the vehicle, the pitch of the siren is constant. The Doppler Effect and Sirens : Waves emitted by a siren in a moving vehicle.
A wave of sound is emitted by a moving vehicle every millisecond. Relative to an onlooker behind the vehicle, the second wave is further from the first wave than one would expect, which suggests a lower frequency.
The Doppler effect can be caused by any kind of motion. In the example above, the siren moved relative to a stationary observer. If the observer moves relative to the stationary siren, the observer will notice the Doppler effect on the pitch of the siren. Finally, if the medium through which the waves propagate moves, the Doppler effect will be noticed even for a stationary observer.
An example of this phenomenon is wind. Quantitatively, the Doppler effect can be characterized by relating the frequency perceived f to the velocity of waves in the medium c , the velocity of the receiver relative to the medium v r , the velocity of the source relative to the medium v s , and the actual emitted frequency f 0 :. The Doppler Effect : Wavelength change due to the motion of source. Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic EM radiation.
EM radiation or photon, which is a quantum of light carries momentum; this momentum is transferred to an object when the radiation is absorbed or reflected. Perhaps one of the most well know examples of the radiation pressure would be comet tails. Although radiation pressure can be understood using classical electrodynamics, here we will examine the quantum mechanical argument.
From the perspective of quantum theory, light is made of photons: particles with zero mass but which carry energy and — importantly in this argument — momentum. Now consider a beam of light perpendicularly incident on a surface, and let us assume the beam of light is totally absorbed.
The momentum the photons carry is a conserved quantity i. There are many variations of laser cooling, but they all use radiation pressure to remove energy from atomic gases and therefore cool the sample. In laser cooling sometimes called Doppler cooling , the frequency of light is tuned slightly below an electronic transition in the atom.
Thus if one applies light from two opposite directions, the atoms will always scatter more photons from the laser beam pointing opposite to their direction of motion typical setups applies three opposing pairs of laser beams as in. Atoms are slowed down by absorbing and emitting photons. In each scattering event, the atom loses a momentum equal to the momentum of the photon. If the atom which is now in the excited state then emits a photon spontaneously, it will be kicked by the same amount of momentum, only in a random direction.
Since the initial momentum loss was opposite to the direction of motion while the subsequent momentum gain was in a random direction , the overall result of the absorption and emission process is to reduce the speed of the atom. If the absorption and emission are repeated many times, the average speed and therefore the kinetic energy of the atom will be reduced. Since the temperature of a group of atoms is a measure of the average random internal kinetic energy, this is equivalent to cooling the atoms.
Key Terms differential equation : An equation involving the derivatives of a function. In this context, we refer to the electric flux and magnetic flux. The Production of Electromagnetic Waves Electromagnetic waves are the combination of electric and magnetic field waves produced by moving charges.
Learning Objectives Explain the self-perpetuating behavior of an electromagnetic wave. Key Takeaways Key Points Electromagnetic waves consist of both electric and magnetic field waves. These waves oscillate in perpendicular planes with respect to each other, and are in phase. The creation of all electromagnetic waves begins with an oscillating charged particle, which creates oscillating electric and magnetic fields.
Difference Between Mechanical and Electromagnetic Waves
Waves come in many shapes and forms. While all waves share some basic characteristic properties and behaviors, some waves can be distinguished from others based on some observable and some non-observable characteristics. It is common to categorize waves based on these distinguishing characteristics. Longitudinal versus Transverse Waves versus Surface Waves. One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction that the waves travel. Categorizing waves on this basis leads to three notable categories: transverse waves, longitudinal waves, and surface waves. A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves.
Wave , propagation of disturbances from place to place in a regular and organized way. Most familiar are surface waves that travel on water , but sound , light , and the motion of subatomic particles all exhibit wavelike properties. In the simplest waves, the disturbance oscillates periodically see periodic motion with a fixed frequency and wavelength. Mechanical waves, such as sound, require a medium through which to travel, while electromagnetic waves see electromagnetic radiation do not require a medium and can be propagated through a vacuum. See also seismic wave. Waves come in two kinds, longitudinal and transverse.
PDF | On Nov 1, , Manuel Vogel published Mechanical and Electromagnetic Vibrations and Waves, by T. Bécherrawy | Find, read and cite.
Energy, a measure of the ability to do work, comes in many forms and can transform from one type to another. Examples of stored or potential energy include batteries and water behind a dam. Objects in motion are examples of kinetic energy. Charged particles—such as electrons and protons—create electromagnetic fields when they move, and these fields transport the type of energy we call electromagnetic radiation, or light.
Named after esteemed physicist James Clerk Maxwell, the equations describe the creation and propagation of electric and magnetic fields. Fundamentally, they describe how electric charges and currents create electric and magnetic fields, and how they affect each other. Magnetic field lines form loops such that all field lines that go into an object leave it at some point. Thus, the total magnetic flux through a surface surrounding a magnetic dipole is always zero.
In physics , mathematics , and related fields, a wave is a propagating dynamic disturbance change from equilibrium of one or more quantities, sometimes as described by a wave equation. In physical waves, at least two field quantities in the wave medium are involved. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium resting value at some frequency. When the entire waveform moves in one direction it is said to be a traveling wave ; by contrast, a pair of superimposed periodic waves traveling in opposite directions makes a standing wave. In a standing wave, the amplitude of vibration has nulls at some positions where the wave amplitude appears smaller or even zero. The types of waves most commonly studied in classical physics are mechanical and electromagnetic. In a mechanical wave, stress and strain fields oscillate about a mechanical equilibrium.
Waves can be divided using several methods. And one such method of differentiating it is by the means of the medium in which they travel. As per the medium, the waves can be differentiated as mechanical and electromagnetic waves. Electromagnetic waves are waves that have no medium to travel whereas mechanical waves need a medium for its transmission. Electromagnetic waves travel in a vacuum whereas mechanical waves do not. The mechanical waves need a medium like water, air, or anything for it to travel. The ripples made in a pool of water after a stone is thrown in the middle are an example of mechanical waves.
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