Emf formula magnetic flux8/6/2023 The device on the baby’s head induces an electrical current in a receiver secured in the bone beneath the skin. Electromagnetic induction used in transmitting electric currents across mediums. Electromagnetic induction can be used in other instances where electric signals need to be conveyed across various media.įigure 3. A current is induced in a receiver secured in the bone beneath the skin and transmitted to electrodes in the inner ear. Sound is picked up by a microphone on the outside of the skull and is used to set up a varying magnetic field. Consider the cochlear implant shown below. This works on the same principle as the audio or video tape mentioned in the last paragraph in which a head reads personal information from your card.Īnother application of electromagnetic induction is when electrical signals need to be transmitted across a barrier. (The discovery that weak changes in a magnetic field in a thin film of iron and chromium could bring about much larger changes in electrical resistance was one of the first large successes of nanotechnology.) Another application of induction is found on the magnetic stripe on the back of your personal credit card as used at the grocery store or the ATM machine. ![]() Today, most hard drive readout devices do not work on the principle of induction, but use a technique known as giant magnetoresistance. However, the input information is carried in digital rather than analog form – a series of 0’s or 1’s are written upon the spinning hard drive. Read heads historically were made to work on the principle of induction. Here recordings are on a coated, spinning disk. Similar principles apply to computer hard drives, except at a much faster rate. Recording and playback heads used with audio and video magnetic tapes. This signal then is sent to a loudspeaker or video player.įigure 2. The different magnetic field orientations of the iron oxide molecules on the tape induces an emf in the coil of wire in the playback head. In the playback mode, the magnetized tape is run past another head, similar in structure to the recording head. As the tape moves past the recording head, the magnetic field orientations of the iron oxide molecules on the tape are changed thus recording the signal. These signals (which are a function of the signal amplitude and frequency) produce varying magnetic fields at the recording head. A signal in the form of a varying input current from a microphone or camera goes to the recording head. This recording head is basically a round iron ring about which is wrapped a coil of wire-an electromagnet (Figure 2). A plastic tape, coated with iron oxide, moves past a recording head. A very important application has to do with audio and video recording tapes. At this juncture, let us mention several that have to do with data storage and magnetic fields. There are many applications of Faraday’s Law of induction, as we will explore in this chapter and others. (See Figure 1.)Īpplications of Electromagnetic Induction Faraday was aware of the direction, but Lenz stated it so clearly that he is credited for its discovery. The direction (given by the minus sign) of the emfis so important that it is called Lenz’s law after the Russian Heinrich Lenz (1804–1865), who, like Faraday and Henry,independently investigated aspects of induction. The minus means that the emf creates a current I and magnetic field B that oppose the change in flux Δ Φ-this is known as Lenz’s law. ![]() The minus sign in Faraday’s law of induction is very important. The units for emf are volts, as is usual. ![]() This relationship is known as Faraday’s law of induction. The equation for the emf induced by a change in magnetic flux is Finally, if a coil has N turns, an emf will be produced that is N times greater than for a single coil, so that emf is directly proportional to N. Second, emf is greatest when the change in time Δ t is smallest-that is, emf is inversely proportional to Δ t. First, emf is directly proportional to the change in flux Δ Φ. Faraday’s experiments showed that the emf induced by a change in magnetic flux depends on only a few factors.
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