Download Induced Current

INDUCED CURRENT

Electromagnetic Induction – The production of
an emf (the energy per unit charge supplied by
a source of electric current) in a conducting
circuit by a change in the strength, position, or
orientation of an external magnetic field.
The magnitude of the induced emf depends on the
velocity of the wire through the magnetic field, the
length, and the strength of the magnetic field.
 No emf is induced if the loop is static or the
magnetic field is constant.

WAYS TO INDUCE AN EMF IN A LOOP OF
WIRE
Move the loop into or out of the magnetic
field (B through loop changing with t).
 Rotating the loop within the magnetic field (θ
changing with t).
 Changing the strength of the magnetic field
through a stationary loop (B changing with
t).
 Altering loop’s shape (A changing with t).

CHARACTERISTICS OF INDUCED CURRENT

Lenz’s Law – The magnetic field of the induced
current opposes the change in the applied
magnetic field.

Lenz’s law allows you to determine the direction of
the induced field, but not the magnitude.
Faraday’s Law of Induction Equation:
emf = -N ∆[AB(cosθ)]/∆t
average induced emf = - of the number of loops
in the circuit x the rate of change of (circuit loop
area x magnetic field component normal to the
plane of the loop) ÷ time change

SAMPLE PROBLEM – (DON’T COPY)

A coil with 25 turns of wire is wrapped
around a hollow tube with an area of 1.8 m2.
Each turn has the same area as the tube. A
uniform magnetic field is applied at a right
angle to the plane of the coil. If the field
increases uniformly form 0.00 T to 0.55 T in
0.85 s, find the magnitude of the induced
emf in the coil. If the resistance in the coil is
2.5 Ω, find the magnitude of the induced
current in the coil.
ALTERNATING CURRENT, GENERATORS, AND
MOTORS


Generator – A device consisting of a coil of wire that
is mechanically rotated in a magnetic field that uses
induction to convert mechanical energy to electrical
energy.
Alternating Current – An electric current that changes
direction at regular intervals.


U.S. frequency of AC is 60 Hz.
Motors – Devices that convert electrical energy to
mechanical energy by using current to supply a
magnetic field that causes the loop to rotate.

Back emf – The emf induced in a motor’s coil that tends
to reduce the current powering the motor.
INDUCTANCE
Mutual Inductance – A measure of the ability of
one circuit carrying a changing current to
induce an emf in a nearby circuit.
 Transformer – A device that changes one ac
potential difference to a different ac potential
difference.

In its simplest form, a transformer consists of two
coils of wire wound around a core of soft iron.
 The coil connected to the source of potential
difference is called the primary coil.
 The coil connected to the resistor is called the
secondary coil.

TRANSFORMER EQUATION
∆V2 = (N2/N1) ∆V1
potential difference in secondary = (number or turns in
secondary coil ÷ number of turns in primary coil) x
potential difference in primary

Because the strength of the magnetic field in the iron
core and the cross-sectional area of the core are the
same for both the primary and secondary windings,
the potential differences across the two windings
differ only because of the different number of turns
of wire for each.
TRANSFORMERS (CONT)
When N2 is greater than N1, the secondary
potential difference is greater than that of the
primary, and the transformer is called a step-up
transformer.
 When N2 is less than N1, the secondary
potential difference is less than that of the
primary, and the transformer is called a stepdown transformer.

PRACTICE PROBLEM

A transformer is used on a 120 V line to
provide a potential difference of 2400 V. If
the primary has 75 turns, how many turns
must the secondary have and is it a step-up
or step-down transformer?
HOMEWORK

Homework worksheet