2006-12-31 09:30:52 · 6 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
LeAnne is right they are call "eddy currents".
emf= electromotive force.
2006-12-31 12:20:31 · answer #1 · answered by HeyDude 3 · 0⤊ 0⤋
in an ac circuit the components of impedance are inductance and resistance - resistance is the ohmic value of the circuit or load under dc condictions and the inductive reactance (or inductance) is the component added to this resistance if altered to an ac circuit.
impedance = resistance + inductive reactance
(they are added together using complex numbers as the inductive reactance is an imaginary component)
the inductive reactance component holds the back emf. it is simply the circuits way of reducing current flow by reducing the voltage over the load (resistance).
ie in a dc circuit the load is 10 ohms with a 10 volt supply therefore the current is 1 amp (ohms law)
now if this same circuit is used and an ac supply is used the load inductive component will come in to play lets say it has an effective inductive reactance of 10 ohms (this could be calculated and is proportaional to the frequency of the ac supply), the effective impedance (or resistance) is increased from the 10 ohms to 10 + j10 ohms. = 14 ohms
if you do the maths you will find the resistance has a voltage drop of about 7V and the impedance has a voltage drop of about 7V
and the overall current flow is reduced to 0.7A
in a rush may have got some of above wrong.. but you get the jist.
quick answer - the back emf is the the voltage over the inductive or capacitive component reducing useful current to the load.
2006-12-31 21:22:00 · answer #2 · answered by Mark G 2 · 0⤊ 0⤋
What your probably talking about is reverse polarity when a transformer is disengaged. It produces a reverse current in the primary windings. Also back emf is caused by induction currents in conduits within a large building and the conduits act as a condenser storing the voltage until it finds a home.
2006-12-31 13:03:58 · answer #3 · answered by Anonymous · 0⤊ 0⤋
A good example is a transformer.
When it is energized, the magnetic field in the primary induces an electric current in the secondary winding. When the primary current is shut off or switches polarity, the secondary windings collapse - and induce an unwanted voltage in the primary winding, and this is the "back emf."
2006-12-31 10:14:01 · answer #4 · answered by LeAnne 7 · 2⤊ 1⤋
When a changing current flows through a wire coil it generates a changing magnetic field. The changing magnetic field then generates a changing voltage which opposes the voltage creating the current. Understand? Simple!
2014-08-14 14:52:34 · answer #5 · answered by Anonymous · 0⤊ 0⤋
you know, its like, you know, whatever
2006-12-31 09:33:45 · answer #6 · answered by mr.jeremy 2 · 0⤊ 2⤋