Survey

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Mathematical descriptions of the electromagnetic field wikipedia, lookup

Skin effect wikipedia, lookup

Electromotive force wikipedia, lookup

Electromagnetism wikipedia, lookup

Magnetism wikipedia, lookup

Electromagnetic field wikipedia, lookup

Ferrofluid wikipedia, lookup

Multiferroics wikipedia, lookup

Friction-plate electromagnetic couplings wikipedia, lookup

Magnetohydrodynamics wikipedia, lookup

Magnet wikipedia, lookup

Electricity wikipedia, lookup

Electric motor wikipedia, lookup

Force between magnets wikipedia, lookup

Lorentz force wikipedia, lookup

Electromagnet wikipedia, lookup

Transcript
```Construction of a simple motor
Level: Secondary 4 / 6
Project aims:
The main purposes of this project are to let students:
1. Learn the working principles of a motor.
2.
Demonstrate their understandings by building a simple motor on their own.
Learning objectives:
1.
2.
3.
Manipulate materials, apparatus and tools for construction.
Propose hypotheses and devise methods for testing.
Infer from observation and experimental results.
Students have to design and build a simple electric motor on their own which can
operate properly.
Students are asked to study factors that would affect the rotating speed of the motor.
Apparatus/Materials:
Any appropriate apparatus and materials proposed by students are welcomed. Typical
examples include magnets, batteries, coils, connecting wires, switches and so on.
Pre-knowledge:
An electric motor converts electrical energy into mechanical motion. When a current
pass through a magnetic field, a force induced will be at perpendicular direction of the
current flow and magnetic field according to the left-hand-rule as shown in Figure 1.
F
B
I
Figure 1: Direction of force produced
when a current passing through a
magnetic field
B-field
N
B-field
S
N
Current
Figure 2: Rotation caused by magnetic
field
and current
S
Current
Figure 3: Rotation caused by magnetic
field after half a turn
and current
Therefore when we arrange the magnets and wires as shown in Figure 2, there would
be a turning force induced. It forces the wire to rotate at the direction of the arrow in
Figure 2. However after a half turn, the turning force would be reversed as shown in
Figure 3. So some techniques have to be used to change direction of current flow in
coil, or just block the current flow in the next half turn so it can continue rotation
under the initial force.
Teachers’ note:
According to Fleming’s left hand rule, a force would be produced which the direction
is perpendicular to the current flow and magnetic field with the relationship,
F  BIAN sin     [1]
Its magnitude depends on the strength of the magnet field B, current I, area A of
circuit coil cutting magnetic field, number of turns of coil (N) and the angle 
between magnetic field and current. Maximum force is generated when the magnetic
field is parallel to the plane of the loop of coil, i.e.   90  .
Actually factors that would affect the rotating speed of the motor are summarized in
equation [1]. Since it is difficult to study it in quantitative way, it is acceptable for
students to describe it qualitatively.
Possible demonstrations:
During briefing, sample of self-made motors can be shown to students as a
demonstration to stimulate their designs. Below shows a simple electric motor design.
Cell
Conducting holder,
negative end
-
Conducting holder,
positive end
+
N
S
Coil
Magnet
Wire,
half of it painted
Wire
Figure 4: The structure of the motor
(Question: When the coil is lain down on the table, shall the top lamination removed
to leave the bottom half painted, or the left lamination removed to leave the right half
painted?)
In Figure 4, when the coil is lain down on the table, the top lamination of the wire has
partially removed. It stops the current flow for half a turn so the coil continues to
rotate under inertia.
Precautions:
Be careful of the heat generated in the motor coil and avoid short circuiting. When
battery is used as a power supply, the maximum voltage should be kept under 3V.
Questions:
1.
2.
Is it possible to let the coil be stator and let the magnet stay in the moving part?
Explain. If it is possible, design a motor in this way.
How can you improve the design of your electric motor such that it can rotate
smoothly, longer or faster?
Extension:
Students can apply their constructed motors to different devices, e.g. to produce a toy
car or make a simple fan etc.
References:
1.
2.
A webpage of many simple motors.
Stan and Serge Pozmantir, SIMPLE ELECTRIC MOTORS
http://www.simplemotor.com
The motor design quoted in figure 4
Ergon Energy, Energy Ed Activities – Experiment: Make an Electric Motor
http://www.ergon.com.au/energyed/activities/make_electric_motor.asp?yf=true&
platform=PC
```
Related documents