Electric Generators
Using a Magnetic Field to
Generate Electricity
Electromagnets, Generators
and Motors, AC & DC
An electromagnet:
electromagnet A coil of
wire with a current going
through it.
Electromagnets can be made
stronger by:
1. Putting an iron or steel bar
in the middle of the coil.
2.
Electromagnets can be made
stronger by:
1. Putting an iron or steel bar
in the middle of the coil.
2. Increasing the number of
turns of the coil.
3.
Electromagnets can be made
stronger by:
1. Putting an iron or steel bar
in the middle of the coil.
2. Increasing the number of
turns of the coil.
3. Increasing the current
through the coil.
•Magnet can be turned on/off
Induced Current
Current
can be induced (created) in a
wire by a changing magnetic field:
- moving a wire inside a field
- changing the magnetic field
(increasing, decreasing or moving)
A
galvanometer (very sensitive
ammeter) can detect these currents
Ways to Induce Current
Turn
magnetic field
off and on
Rotate magnet in coil
Rotate coil in
magnetic field
Move magnet in and
out of coil
Examples
It
doesn’t matter whether the magnetic
field moves, or the conducting wire
moves, the result is the same.
Generators
Devices
that turn mechanical energy
into electrical energy
Mechanical energy supplied by spinning
wheel, running water, windmill, steam
turbine
Types of Generators
Examples
- bicycle generator
(spinning wheel turns coil inside a magnet
which generates electricity to run lights etc.)
- hydroelectric power plant
(running water turns turbine, which spins a
coil in a magnetic field and generates large
amounts of electricity)
With Alternating Current,
Current (AC),
the current keeps on changing
direction.
direction
cycle
Frequency is how many cycles
per second there are in AC.
1 cycle per second is called
one Hertz (Hz).
Hz
The current coming into our
homes is 60 Hz (or 60 cycles
per second)
The current changes direction
120 times each second!
With Direct
Current
(DC), the
current only
flows one
way through
the circuit.
Direct Current (DC)
Current
that goes in only one direction
The type of current produced by
chemical cells.
Used for flashlights, portable stereos
etc.
Many household devices run on DC that
is converted from AC (TV’s, computers)
– Electric Motors:
• An electrical motor is an electromagnetic device
that converts electrical energy into mechanical
energy.
• A motor has two working parts - a stationary
magnet called a field magnet and a cylindrical,
movable electromagnet called an armature.
• The armature is on an axle and rotates in the
magnetic field of the field magnet.
• The axle is used to do work.
Electric Motors
Electricity
is added to make motor turn
and get usable mechanical energy
Reverse of a generator
Electric motor
Red = North pole
Green = South
pole
Opposite
polarities attract
1. A simple DC electric motor. When
the coil is powered, a magnetic field is
generated around the armature. The left
side of the armature is pushed away
from the left magnet and drawn toward
the right, causing rotation.
2. The armature continues to rotate
3. When the armature becomes
horizontally aligned, the commutator
reverses the direction of current
through the coil, reversing the
magnetic field. The process then
repeats.
Transformers
Allow
current flow to be adjusted to any
voltage
Used in electricity transmission and in
most electrical devices
Changes voltage using two linked
electromagnets
Transformers
Step-up transformer:
– more coils on the
secondary coil (right
side)
Step-down transformer:
-more coils on the
primary coil (left side)
Homework
Chapterrrrrrrrrrrrr
Jack
is an idiot.
4 Review