Chapter 21- Electromagnetic induction and faraday's law Flashcards
What is an induced current?
a constant magnetic field produces no current in a conductor, a changing magnetic field can produce an electric current, called an induced current
What is faraday’s theory?
a changing magnetic field induces an emf.
What happens when you move a magnet in a current? (removed and other)
If the magnet is quickly removed, a current is induced in the opposite direction (B through the coil decreases). Furthermore, if the magnet is held steady and the coil of wire is moved toward or away from the magnet, again an emf is induced and a current flows
that the more rapidly the magnetic field changes…what happens to the induced emf?
the more rapidly the magnetic field changes, the greater the induced emf.
What is emf proportional to? magnetic……
the emf is proportional to the rate of change of the magnetic flux , passing through the circuit or loop of area A.
What is Lenz’ law?
a current produced by an induced emf moves in a direction so that the magnetic field created by that current opposes the original change in flux.
An induced emf is always in a direction that opposes the original change in flux that caused it.
What are the two distinct magnetic fields?
(1) the changing magnetic field or flux that induces the current,
(2) the magnetic field produced by the induced current (all currents produce a magnetic field).
The second (induced) field opposes the change in the first.
What happens when the distance between the coil and magnet decreases? (magnet moves upwards)
The magnet’s magnetic field (and number of field lines) through the coil increases, and therefore the flux increases. The magnetic field of the magnet points upward. To oppose the upward increase, the magnetic field produced by the induced current needs to point downward inside the coil.
What happens when magnet moves down in a coil?
the flux decreases (because the magnet is moved away and B decreases), so the induced current in the coil produces an upward magnetic field through the coil that is “trying” to maintain the status quo.
When is faraday’s law valid?
Faraday’s law is valid as long as B, l, and v are mutually perpendicular
What is motional emf?
An emf induced on a conductor moving in a magnetic field
How is there an induced emf when a rod moves through a uniform magnetic field when the rod is not in contact?
If the rod is not in contact with the U-shaped conductor, electrons would collect at the upper end of the rod, leaving the lower end positive (see signs in Fig. 21–11b). There must thus be an induced emf.
How is there an induced emf when a rod moves through a uniform magnetic field when the rod is in contact?
If the rod is in contact with the U-shaped conductor (Fig. 21–11a), the electrons will flow into the U. There will then be a clockwise (conventional) current in the loop.
What does a transformer do?
is a device for increasing or decreasing an ac voltage
What does transformer consist of?
A transformer consists of two coils of wire known as the primary and secondary coils. The two coils can be interwoven (with insulated wire); or they can be linked by an iron core which is laminated to minimize eddy-current losses
