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.
natural 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.
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.
poles 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 introducesing the topic of day and spells out the learning outcomes they
will possess after the study. Acquaint students with the following issues:
•The theme of the lesson
•The objectives of the lesson
•The criteria of success for
•The plan of events for the
•Pre-teach the subject
Learners will share their
experiences with electromagnets and solenoids
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.
Then teacher will explain the
properties and applications of electromagnets and solenoids. Describe, discuse,
and explain the workings and applications of electromagnets. Ask learners to
make their own electromagnets and to determine factors that affect their
strength. Give questions on a worksheet.
Learners will discuss their
experiences with electromagnets. Watch videos on electromagnets. Make their own
electromagnets and try to determine factors that determine their strengths.
Answers questions about the videos.Work in groups to develop presentations about applications
of electromagnets. Attempt questions on the worksheet
•Highlights key concepts,
definitions, and equations learnt using the concept map.
•Asks students to do
questions on the worksheet provided.
•Looks forward to the next
•Attempt the questions given
by the teacher.
•Summarize the main concepts,
definitions, and equations learnt.
•Reflect on their own
•Evaluate their own work and
the work of their classmates.
•Complete the flipped reading
and research assignment before the next lesson.
•Complete the specified
thinking tasks for this lesson.
•Should complete worksheet
given by teacher
Additional multilevel (on
assigns questions 1, 2, 3, 4 to weak students, questions 5 and discussion 1, 2
to the average students, questions discussion 3, 4 to the strong students.
Recommendations for formative assessment
work students will do by themselves. Then teacher will show answers on the
board. Learners will check their answers through the class.
Answers, criteria for
assignments, additional materials for the lesson
Q. No 1:
Three sources of magnetic fields are:
(a) Permanent magnet
(c) Current-carrying conductor
Q. No 2:
In an electromagnet the magnetic field is created through electric current in a wire-wound coil and strengthened by a soft-iron core. As soon as you turn off the power, the soft-iron core loses its magnetisation.
A permanent magnet is made of ferromagnetic material, which is magnetised by a strong external magnetic field. The magnetically hard material that is used keeps part of its magnetisation after the external magnetic field is turned off.
Q. No 3:
They are 1) bar magnet 2) horseshoe magnet 3) cylindrical magnet 4) solenoid 5) electro magnet 6) permanent magnet
A natural magnet is a magnet that occurs naturally in nature. All natural magnets are permanent magnets, meaning they will never lose their magnetic power. Natural magnets can be found in sandy deposits in various parts of the world. The strongest natural magnet material is lodestone, also called magnetite
The difference is that natural magnets are much more stronger than artificial magnets
Q. No 4:
Solenoid is coil having n number of turns of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is passed through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure.
When the north pole of a bar magnet is brought near to the end connected to the negative terminal of the battery, then the solenoid repels the bar magnet. It means the end of solenoid which is connected to the negative terminal of the battery behaves as north pole as like poles repel each other similarly the other and behaves as a south pole.
Q. No 5:
As nouns the difference between magnet and solenoid is that magnet is a piece of material that attracts some metals by magnetism while solenoid is a coil of wire that acts as a magnet when an electric current flows through it.
Possible Ans: As electricity passes through a wire, some of the electrical energy is converted to heat. The more current that flows through a wire, the more heat is generated. If double the current passing through a wire, the heat generated will increase 4 times! If triple the current passing through a wire, the heat generated will increase 9 times! Things can quickly become too hot to handle.
Depending on the thickness of the wire, might be able to get a meter of wire wrapped in a single layer along a core only a few centimeters long. With each turn, you add the magnetic force. And we are coiling it such that the lines of magnetic force are parallel and pointing in the same direction. We can add more coils on top of the first row, and this just adds more field strength. In technical terms, every coil of wire increases the "magnetic flux density" (strength) of magnet. The magnetic field on the outside of the coil resembles a bar magnet. The right hand rule can be applied to determine the North pole: if to hold the coil in your right hand, and the current flow is in the direction our fingers are pointing, the North pole is the end where your thumb is.
A thicker core might make a more powerful magnet. Just make certain that the material you choose can be magnetized.
If a permanent magnet is not attracted to core, it will not make a good electromagnet. An aluminum bar, for example, is not a good choice for your magnet's core.
Theoretical material for the lesson, definitions for concepts
An electromechanical relay is a solenoid used to make or break mechanical contact between electrical leads
Learners will discuss their experiences with electromagnets
A permanent magnet is made of ferromagnetic material, which is magnetised by a strong external magnetic field