# ELECTROMAGNETIC PHENOMENA1. Electromagnetic inductionMagnetic flux is a measurement of the total magnetic field B which passes through a givenarea. It is a useful tool for helping describe the effects of the magnetic force on somethingoccupying a given area. If the magnetic field is constant, the magnetic flux passing through asurface of area A is= B ·A coseNormal to AThe SI unit of magnetic flux is the Weber (Wb).Faraday lawWhen a current conducting wire or coil is moved through amagnetic field a voltage (EMF) is generated which depends onthe magnetic flux through the area of the coil. This is an exampleof the phenomenon of electromagnetic induction; the currentthat flows in this situation is known as an induced current.Faraday's Law relates the average induced EMF in terms of thetime rate of change of the total magnetic flux through a current8 cosBA cos e- B,Aconductor or coil.E = NAtFinally, if a coil has N turns, an emf will be produced that is N times greater than for a singlecoil, so that emf is directly proportional to N.The magnetic field strength (magnitude) produced by a long straight current-carryingwire is found by experiment to be B = , where I is the current, r is the shortest distance tothe wire, and the constant = 470x10 7T m/A is the permeability of free space.Magnetic field produced by a current-carrying circular loop. There is a simple formula forthe magnetic field strength at the center of a circular loop. It is B = where R is the radiusof the loop. One way to get a larger field is to have Nloops; then, the field is B = N.2. Electromagnetic fieldAt every instant the ratio of the magnitude of the electric field to the magnitude of the magneticfield in an electromagnetic wave equals the speed of light.2R"Emax EВтак в3. Electromagnetic wavesThe magnitudes electric field strength E and magnetic fieldstrength B in electromagnetic wave vary with x and iaccording to the expressionsE (x, t) = Egsin(kx – wt)B(x, t) = Bosin(kx – wt)Here k = and w =with 2 the wavelength and Tthe period of the wave (T=1/fwhere fis the frequency of oscillationof the wave). The speed of the wave is given by v = c = as /k.There are many types of waves, such as water waves and even earthquakes. Among the manyshared attributes of waves are propagation speed v, frequency f, and wavelength 2. These arealways related by the expression:v = af Electromagnetic waves, like visible light, infrared, ultraviolet, X-rays, and gamma rays don'tneed a medium in which to propagate; they can travel through a vacuum.Speed of electromagnetic wave in vacuumC =-Taking the permittivity of free space eo = 8.85 · 10-12 F/m and permeability of free space jto- 4T0x10 "Ťm/A, c = 3 · 10° m/sec.TaeLUeslenaspectTypeEMProductionApplicationswaveCommunicationsRemote controlsAcceg charges a themal Conmurictons Over Dep hegRadarRepas consband useRado& TVAcceng chargesMRIMicrowaesCell phoeThermal gtons & econThemal magngAbsorbed byamospherePhotonynhesis HumanhandGrente eectThermal agatons &econApeveThermal agkatons &elecon Seteton CancerOmne depleon CancercaingVnin DprotuctonMukal gsCancer therapyMekal gosCancer therapyoonteo sits ad Medkal Setyt cotCance cgCancer csgHaon dmgeNuckmedkinetiecutyCamma mysNucw decay4. Energy in electromagnetic waveElectromagnetic waves can bring energy into a system by virtue of their electric and magneticfields. These fields can exert forces and move charges in the system and, thus, do work on them.Once electromagnetic wave has created, the fields carry energy away from a source. IntensityI of electromagnetic wave is energy per area A per time t or power P per area. Intensity ismeasured in W/m²:1 = EnergyThe energy carried and the intensity I of an electromagnetic wave is proportional to E and B.In fact, for a continuous sinusoidal electromagnetic wave, the average intensity I is given bywhere c is the speed of light, a» is the permittivity of free space, and Eo is themaximum electric field strength.The average intensity of an electromagnetic wave I can also be expressed in terms of themagnetic field strength / =5. Radiation pressure is the pressure exerted upon any surface due to the exchange ofmomentum between the object and the electromagnetic field. The radiation pressure Pexertedon the perfectly absorbing surface is: P = {where Bo is the maximum magnetic field strength.6.The electromagnetic wave intensity at distance r from the source /:here Pis power.

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Give an order of magnitude estimate, based on Faraday’s law, of the maximum induced emf detected by a search coil with a 0.2 m diameter 1 cm away from a long neuron which carries an average current of 10 pA switched on in 1 ms. Suppose, that neuron is long straight current caring wire.

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The given values are, Step 2

Write the expression for the induced electromotive force (emf). ...

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