Theoretical material for the lesson,
definitions for concepts
Story of Magnet
There is an island called Magnesia in Greece. Years ago, shepherds here
complained that their wooden shoes with nails stayed stuck to the grounds. They
were unable to walk further. This was the story behind the discovery of
magnetism. So, how did this relate to the presence of magnetic fields?
Actually, this island had lots of magnetic ore deposits!
Sounds really interesting! Doesn’t it? Let us now look at this topic in
greater detail and discuss magnets and their properties. The property of an
object by virtue of which it can attract a piece of iron or steel is
called magnetism. The object itself is called a magnet. Now, we will look
at the types of magnets.
magnet is an ore of iron that attracts small pieces of iron, cobalt, and nickel
towards it. It is usually an oxide of iron named Fe3O4. Magnetite
or lodestone is a natural magnet.
that is prepared artificially form the artificial magnets. Examples include an
electromagnet, a magnetic needle, horseshoe and bar magnets etc. According to
the molecular theory, every molecule of a magnetic substance, irrespective of
whether or not it is magnetized.
are the two points near but within the ends of the magnetic materials, at which
the entire magnetism can be assumed to be concentrated. The poles always occur
in pairs and they are of equal strength. Like poles repel each other and unlike
poles attract each other. This is all the basic information about magnets. Now,
we will look deeper into the properties of magnets.
A solenoid is
simply a specially designed electromagnet. A solenoid usually consists of a
coil and a movable iron core called the armature. Here's how it
works.When current flows through a wire, a magnetic field is set up around the
wire.If we make a coil of many turns of wire, this magnetic field becomes many
times stronger, flowing around the coil and through its center in a doughnut
shape. When the coil of the solenoid is energized with current, the core moves
to increase the flux linkage by closing the air gap between the cores. The
movable core is usally spring-loaded to allow the core to retract when the current
is switched off. The force generated is approximately proportional to the
square of the current and inversely proportional to the square of the length of
the air gap.
are inexpensive, and their use is primarily limited to on-off applications such
as latching, locking, and triggering. They are frequently used in home
appliances (e.g. washing machine valves), office equipment (e.g. copy
machines), automobiles (e.g. door latches and the starter solenoid), pinball
mahines (e.g., plungers and bumpers), and factory automation.
electromechanical relay is a solenoid used to make or break
mechanical contact between electrical leads. A small voltage input to the
solenoid controls a potentially large current through the relay contacts.
Applications include power switches and electromechanical control elements. A
relay performs a function similar to a power transistor but has the capability
to switch extremely large currents if necessary. However, transistors have a
much shorter switching time than relays.
illustrated in figure 2, a voice coil consists of a coil that
moves in a magnetic field produced by a permanent magnet and intensified by an
iron core. The force on the coil is directly proportional to the current in the
coil. The coil is usually attached to a movable load such as the diaphragm of
an audio speaker, the spool of a hydraulic proportional valve, or the
read-write head of a computer disk drive. The linear response and bidirectional
capability make voice coils more attractive than solenouds for control
Additional guidelines for organizing a
Lesson starts with introducing a lesson topic.Summary of the main properties of magnets in terms of field and
types of materials, magnetic and non-magnetic properties
Then students can deduce topic
of the lessen and objectives, for clarification you can show topic and the
learning objectives on the presentation.
vocabulary & terminology will be presented to the students and their
activities during the research work will be explained.
teacher using Power Presentation and whiteboard, used to introduce terms
related to magnetic fields in connection with the design of an electromagnet.
At this time students answer questions in a presentation, students take notes
and ask questions online. Assignment
for the teacher: distribute worksheets and assignments for practical work. Work
in pairs. It is necessary to assemble the electromagnet. Instruments: nail,
copper wiring, galvanometer, voltmeter, paper clips, magnetic needle.
How to make an artificial magnet? Student individual groups collect electromagnets using the materials provided, in accordance with these practical instructions. Teacher to encourage students to create devices. Constantly monitor, including how well they can organize and work together in a team.After students have received instructions for assembling an electromagnet, they should - collect solenoid - assemble an electromagnet (understand how a solenoid differs from an electromagnet) -determine the dependence of the magnetic field of the solenoid on the strength of the electric current (change the electric current, count the number of clips) - -determine the dependence of the magnetic field of the solenoid on the number of turns of the coil (measure the electric current, count the number of clips)).
Formative evaluation questions.
be reflection and at the lesson teacher gives homework.
Additional multilevel (on
assigns questions fill the table with some mistakes to weak students, questions
fill the table without mistakes to the average students, questions fill the
table correctly and high level question to the strong students.
Recommendations for formative assessment
Experiment will be done by group. In
the group should be 4 students.
Answers, criteria for
assignments, additional materials for the lesson
Teacher should do this experiment and make
his/her answer sheet which would be correct by his/her experimental apparatus.
Theoretical material for the lesson, definitions for concepts
An electromechanical relay is a solenoid used to make or break mechanical contact between electrical leads