30.14
Correntes de Foucault
Uma vez que as correntes de Foucault ocorrem apenas em condutores, os ímãs podem separar metais de outros materiais. Por exemplo, em um centro de reci…
As correntes parasitas são um loop de corrente elétrica induzida dentro de um condutor devido a uma mudança no campo magnético.
Nas correntes parasitas, os elétrons giram em um loop circular perpendicular ao campo magnético.
Considere um solenóide conectado a uma fonte CA. Como resultado da corrente variável, o campo magnético produzido pelo solenóide também varia.
Em seguida, uma placa metálica é mantida próxima ao solenóide, o que resulta na geração de correntes parasitas na placa.
Essas correntes desencadeiam perda de energia, pois produzem calor desnecessário.
Por exemplo, a energia elétrica é desperdiçada como calor no núcleo do transformador devido à formação de correntes parasitas.
Este efeito indesejável pode ser utilizado em várias aplicações.
Quando um fogão de indução composto por uma bobina metálica é ligado, uma corrente CA começa a fluir na bobina.
Isso gera um campo magnético variável. Como resultado da mudança do fluxo magnético, correntes parasitas se desenvolvem na base do vaso metálico e o aquecem sem aquecer a placa superior não condutora do fogão.
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Q1: What are eddy currents and how do they form in a conductor?
Eddy currents are loops of electric current induced within a conductor due to a changing magnetic field. Electrons swirl in circular loops perpendicular to the magnetic field direction. When a varying magnetic field passes through a conductor, such as a metallic plate near a solenoid with AC current, the changing magnetic flux induces these circular currents throughout the material.
Q2: Why do eddy currents cause energy loss in transformers?
Eddy currents generate unnecessary heat as they flow through the transformer core, wasting electrical energy. This occurs because the variable magnetic field from the AC current induces circular currents in the conductive core material. The resistance of these currents converts electrical energy into thermal energy, reducing transformer efficiency.
Q3: How do induction cooktops use eddy currents to heat food?
Induction cooktops contain electromagnets beneath the surface that generate rapidly varying magnetic fields. These changing fields produce eddy currents in the pot's conductive base, such as iron or steel. The eddy currents generate heat that warms the pot and its contents without heating the non-conducting top plate, providing high efficiency and fast response times.
Q4: How do metal detectors use eddy currents to identify metals?
Metal detectors consist of a primary coil carrying alternating current and a secondary coil where current is induced. When metal approaches the detector, an eddy current forms in the metal, causing a change in the induced current within the secondary coil. This change triggers a signal, such as a shrill noise, alerting the user to the presence of metal.
Q5: Why are eddy currents effective for braking in roller coasters?
Roller coasters use powerful rare-earth magnets, such as neodymium magnets, with metal fins containing copper that pass through the magnetic field. Eddy currents induced in the fins slow the vehicle smoothly without mechanical contact. This braking method is safer because weather conditions like rain do not affect performance, though another braking form is needed for complete stops.
Q6: How do recycling centers use eddy currents to separate metals from trash?
Recycling centers use powerful magnets beneath ramps where trash is dumped. Eddy currents induced in conductors slow them down, while nonmetals pass through unaffected. This separation works for all metals, not just ferromagnetic ones, allowing efficient sorting of metallic materials from other waste materials.
Q7: What is the relationship between eddy currents and induced electric fields?
Eddy currents result from induced electric fields created by changing magnetic flux through a conductor. According to induced electric fields applications, these electric fields drive electrons in circular paths, forming the characteristic eddy current loops. The strength and direction of eddy currents depend on the rate of magnetic field change and the conductor's properties.