Download Motors and AC Generators KLT

Motors
Coil in a Magnetic Field
How does an electric motor
work?
DC Electric Motor
Simulation
Specification Aims
By the end of this lesson
you should be able to…
• Understand that a
wire at right angles to
a magnetic field
experiences a force.
• Explain how to use
Fleming’s Left Hand
Rule to predict the
direction of the force
experienced.
• Explain how a DC
electric motor is
maintained .
axle
brushes
battery
coil
commutator
magnets
• Describe the effect of
changing:
– the size of the
current
– the number of
turns
– the strength of the
magnet
Motors
Generators
How does a Generator
Work?
How does a Generator Work?
Increasing the size of the induced
current
How can the
increase
Specification Aims
By the end of this lesson
you should be able to…
• Describe how an
a.c. generator
works, including
size of an induced current be increased?
the function of the
the speed at which the coil rotatesslip rings.
increase the strength of the magnetic field•
increase the number of turns in the coil
increase the total area of the coil.
In a power
station
generator, an
electromagnet is
often used as
this can provide
a stronger
Explain how a
Cathode Ray
Oscilloscope
(CRO) works and
how it can be used
to construct
voltage time
graphs.
• Explain the
difference between
alternating current
(AC) and direct
current (DC).
Factors affecting induced
current
What is alternating current
(a.c.)?
Alternating current (a.c.) is an electric
current that is constantly changing
direction. Alternating current is
produced by most generators and is
used in mains electricity.
Motors often work using
alternating current. The
voltage of alternating
current is easily
changed with a
transformer.
Alternating current can
be transferred efficiently
over large distances.
Specification Aims
By the end of this lesson
you should be able to…
• Describe how an
a.c. generator
works, including
the function of the
slip rings.
• Explain how a
Cathode Ray
Oscilloscope
(CRO) works and
how it can be used
to construct
voltage time
graphs.
• Explain the
difference between
alternating current
(AC) and direct
current (DC).
A.C or
D.C.
The difference between alternating
voltage
voltage
current (a.c.) and direct current (d.c.)
can be seen using an oscilloscope.
For each current, the oscilloscope trace is
d.c.
a graph showing how the voltage of an
time with time.
electricity supply varies
peak forward
voltage
peak reverse
voltage
a.c.
time
Specification Aims
By the end of this lesson
you should be able to…
• Describe how an
a.c. generator
works, including
the function of the
slip rings.
• Explain how a
Cathode Ray
Oscilloscope
(CRO) works and
how it can be used
to construct
voltage time
graphs.
• Explain the
difference between
alternating current
(AC) and direct
current (DC).
voltage
A.C or
D.C.
Specification Aims
By the end of this lesson
you should be able to…
d.c.
time
The voltage of a d.c. supply is steady and always in
the same direction.
voltage
The voltage of an a.c. supply follows a repeated
pattern: it rises to a peak, returns to zero changes
direction and so on.
peak forward
a.c.
voltage
peak reverse
voltage
time
• Describe how an
a.c. generator
works, including
the function of the
slip rings.
• Explain how a
Cathode Ray
Oscilloscope
(CRO) works and
how it can be used
to construct
voltage time
graphs.
• Explain the
difference between
alternating current
(AC) and direct
current (DC).
Frequency of A.C.
voltage
The frequency of a.c. electricity is the
number of complete cycles per second,
which1iscomplete
measuredcycle
in hertz (Hz).
peak forward
voltage
a.c.
time
peak reverse
voltage
The a.c. frequency can be determined
from an oscilloscope by counting the
number
of complete
waves per
unit
time.
If the frequency
is increased,
the
number
of complete waves shown on the screen
increases. For example, if the frequency is
Specification Aims
By the end of this lesson
you should be able to…
• Describe how an
a.c. generator
works, including
the function of the
slip rings.
• Explain how a
Cathode Ray
Oscilloscope
(CRO) works and
how it can be used
to construct
voltage time
graphs.
• Explain the
difference between
alternating current
(AC) and direct
current (DC).
Generators
The coil is rotated
manually, by a steam/water/wind powered turbine
As the coil spins, flux linkage changes and so
an emf is induced.
AC Generators
Consider one rotation of the coil
Flux Linkage
0
180
360
Flux Linkage
0
AC Generators
180
360
180
360
Induced emf
0
AC Generators
The gradient of the flux linkage graph represents
the induced emf.
Maximum gradient = maximum emf
ε = ε0 sin 2 π f t
epsilon 0 = peak emf