tag:blogger.com,1999:blog-2361412992308994774.post8463463450923505530..comments2023-11-19T19:19:12.773-05:00Comments on Dealing with Creationism in Astronomy: Electric Universe: Peer Review Exercise 3W.T."Tom" Bridgmanhttp://www.blogger.com/profile/10889134728080314165noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-2361412992308994774.post-71417510257984058322012-06-04T21:16:53.843-04:002012-06-04T21:16:53.843-04:00To gristy BSc,
Scott says: "Magnetic fields ...To gristy BSc,<br /><br />Scott says: <i>"Magnetic fields are created by and moved around by electric currents – nothing else."</i><br /><br />The 'nothing else' suggest Scott was <i>not</i> including such configurations. <br /><br />An EM wave, and other configurations, once started, can maintain, and even increase magnetic field strength without an external current (using only induced currents and energy from other sources). This is why the professional literature will generally state that currents create magnetic fields, but not *only* currents can create magnetic fields. The driving mechanisms are much more complex to be limited by such dogmatism.<br /><br />The displacement current term applies to capacitors in vacuum as well. As the current flows to the capacitor plate, the plate accumulates charge which changes the electric field in the region. This is necessary for charge to be conserved in the integral form of Ampere's Law.<br /><br />In a dielectric, you get a polarization effect, which is why the displacement current is usually written in terms of D = epsilon*E. In an ideal (non-leaky) dielectric, you will get dielectric polarization, but not any significant net current flow from this charging (check the links I provided in the post).W.T."Tom" Bridgmanhttps://www.blogger.com/profile/10889134728080314165noreply@blogger.comtag:blogger.com,1999:blog-2361412992308994774.post-35712218842955342942012-06-04T05:35:13.593-04:002012-06-04T05:35:13.593-04:00True, an EM wave does not have to be maintained, b...True, an EM wave does not have to be maintained, but only created by acceleration of charge. I dont think D.S. over looked that.<br /><br />wrt to displacement current being ficticious I need to correct myself. I was considering only the case of a vacuum capacitor. In a dielectric material real current is present ( electrons shift within their atomic position ) in which case magnetic fields are induced by real current.gristy BScnoreply@blogger.comtag:blogger.com,1999:blog-2361412992308994774.post-49300760724421189362012-06-03T21:41:36.130-04:002012-06-03T21:41:36.130-04:00To gristy BSc,
I covered this case pointing out t...To gristy BSc,<br /><br />I covered this case pointing out that we can examine electromagnetic waves by just considering E & B fields, without consideration of the original current which started the wave.<br /><br />E&M waves are a direct consequence of this term. Propagating electromagnetic waves in free space have dE/dt nonzero and J=0.<br /><br />If you want to say the displacement current is ficticious, then are you saying electromagnetic waves are ficticious?W.T."Tom" Bridgmanhttps://www.blogger.com/profile/10889134728080314165noreply@blogger.comtag:blogger.com,1999:blog-2361412992308994774.post-1055984785855550522012-06-03T21:10:13.103-04:002012-06-03T21:10:13.103-04:00'This equation can also be true if J is zero a...'This equation can also be true if J is zero and dE/dt is non-zero'<br /><br />That can only be true for points in time. Over any length of time with dE/dt<>0, current must flow i.e J>0. <br /><br />It's therefore incorrect to say Ampere's law asserts magnetic fields can exist without electric current.<br /><br />wrt your reference to displacement currents as an example of a magnetic field without current<br /> : A displacement current is a ficticious construct used for convenience. <br />The magnetic field associated with the displacement current is not physically created or maintained by the ficticious displacement current, but rather by the real current in the capacitor ( or other object with displacement current ) terminals.gristy BScnoreply@blogger.com