Download CH22 Induction and Alternating Current READ NOTES Serway

PHYSICS
Name __________________________________________ Date _____________
Energy: Conservation and Transfer
Phy.3.2 Explain the
concept of
magnetism.
Phy.3.2.1 Explain the relationship between magnetic domains and magnetism.
Phy.3.2.2 Explain how electric currents produce various magnetic fields.
Phy.3.2.3 Explain how transformers and power distributions are applications of
electromagnetism.
Text Reference: Physics (Serway) Chapter 22
Induction and Alternating Current
Read PHYSICS IN ACTION on page 793. We will see how electric guitars use the principles of induction and
alternating current.
22-1 Induced Current
MAGNETIC FIELDS AND INDUCED EMFS
Recall in Chapter 20 Circuits you were asked if it was possible to produce an electric current using only wires and no
battery. So far, all electric circuits that you have studies have used a battery or an electrical power supply to create a
potential difference (a.k.a. emf, electromotive force) within a circuit. In both of these cases, an emf increases the electrical
potential energy of charges in the circuit, causing them to move through the circuit and create current.
It is also possible to ____________________ a current in a coil _____________________ the use of a battery or an
electrical power supply. Just as a magnetic field can be formed by a current in a circuit, a current can be formed by
_________________ a portion of a closed electric circuit through an external _________________________ field, as
indicated in Figure 22-1.
Write the definition of electromagnetic induction:
Consider a circuit consisting of only a resistor in the vicinity of a magnet. There is no battery to supply a current. If
neither the magnet nor the circuit is _____________________ with respect to the other no current will be present in the
circuit. But if the circuit ___________________ toward or away from the magnet or the magnet __________________
toward or away from the circuit, a __________________________ is induced. As long as there is relative
_________________________ between the two, a _____________________ can form between in the circuit.
The _____________________________ of charges by the magnetic force induces an emf.
It may seem strange that there can be an induced emf and a corresponding induced current without a battery of similar
source of electrical energy. Recall that in the previous chapter a moving charge can be ______________________ by a
magnetic field. This _________________________ can be used to explain how an emf occurs in a wire that moves
through a magnetic field.
Draw Figure 22-2 and copy the caption:
The ______________ between a magnetic field and a circuit affects induction.
_____________________ in the number of magnetic field lines induces a current.
Copy Table 22-1 Ways of inducing a current in a circuit:
CHARACTERISTICS OF INDUCED CURRENT
Copy Figure 22-4 and the caption:
Copy Figure 22-5 and the caption:
The rule for finding the direction of the induced current is called Lenz’s law and is expressed as follows:
Faraday’s law of induction
Because of the principle of energy conservation, Lens’s law allows you to determine the direction of an induced current in
a circuit. Lenz’s law does not provide information on the magnitude of the induced current or the induced emf. To
calculate the magnitude of the induced emf, you must use Faraday’s law of magnetic induction.
Write FARADAY’S LAW OF MAGNETIC INDUCTION equation:
APPLICATIONS OF INDUCTION: door bells, tape recorders, electric door locks, car trunk release
22-2 Alternating current, generators, and motors
GENERATORS
In the previous section you learned that a current can be induced in a circuit either by changing the magnetic field
________________________ or by ________________________ the circuit loop in or out of the magnetic field. Another
way to induce a current is to change the ________________________________ of the loop with respect to the magnetic
field.
This second approach to inducing a current represents a _________________________ means of generating
electrical energy. Write the definition of generator:
A generator produces a continuously ______________________ emf.
Draw Figure 22-12 and copy the caption:
Alternating current changes direction at a constant ____________________________________.
Write the definition of alternating current:
On page 807, copy the
Did you know?
Draw Figure 22-13 and copy the caption:
22-3 Inductance
MUTUAL INDUCTANCE
The basic principle of electromagnetic induction was first demonstrated by Michael Faraday. His experimental apparatus,
which resembled the arrangement shown in Figure 22-18, used a coil connected to a switch and a battery instead of a
magnet to produce a magnetic field.
This coil is called the ____________________ coil, and its circuit is called the _________________________ circuit.
The magnetic field is strengthened by the magnetic properties of the __________________ ring around which the
______________________ coil is wrapped.
A second col is wrapped around another part of the iron ring and connected to a galvanometer. An ___________
is induced in this coil, called the ___________________________ coil, when the magnetic field of the ______________
coil is changed.
The magnitude of this emf is predicted by Faraday’s law of induction. Write the definition of mutual
inductance:
TRANSFORMERS
It is often desirable or necessary to change a small ac potential difference to a _____________ one or to change a large
potential difference to a ___________________ one. The device that makes these conversions possible is the
transformer.
In its simplest form, an ac transformer consists of two coils of wire wound around a core of soft iron, like the
apparatus for the Faraday experiment. Draw Figure 22-19 and copy the caption:
Copy the page 816 version of the TRANSFORMER EQUATION as the ratio of voltages to number of
turns:
When N2 is greater than N1, the secondary potential difference is __________________________ than that of the primary,
and the transformer is called a ____________________________________ transformer. When N2 is less than N1, the
secondary potential difference is ________________________ than that of the primary, and the transformer is called a
________________________________________ transformer.
It may seem that a transformer provides something for nothing. When the voltage is stepped up, there is a
proportional decrease in the ___________________________________.
Real transformers are not perfectly __________________________________________.
The transformer equation assumes that there are __________ power losses between the transformer’s primary and its
secondary. Real transformers typically have efficiencies ranging from 90 to 99 percent.
Study SAMPLE PROBLEM 22D and solve PRACTICE 22D problems – they WILL be on your NCFE.