PHY_10_59_V2_TG_Artificial magnets. Solenoid
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PHY_10_59_V2_TG_Artificial magnets. Solenoid

Оценка 5
docx
08.05.2020
PHY_10_59_V2_TG_Artificial magnets. Solenoid
PHY_10_59_V2_TG_Artificial magnets. Solenoid.docx

Theoretical material for the lesson, definitions for concepts 

The 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 Magnets

A 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.

Artificial Magnets

A 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.

The 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.

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.

Solenoids 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.

An 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.

As 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 applications.

 

Additional guidelines for organizing a lesson 

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 lesson

      The plan of events for the lesson

      Pre-teach the subject specific vocabulary.

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.

Then Subject-specific 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

A BBC Bitesize page on electromagnets:

http://www.bbc.co.uk/schools/ks3bitesize/science/energy_electricity_forces/magnets_electric_effects/revise4.shtml

A short video about electromagnets:

http://www.youtube.com/watch?v=LWey-OImGGs

This animation gives a simple explanation of the domain theory for the magnetisation of an iron rod:

http://www.youtube.com/watch?v=85dIRfKMlwM

Investigation of a current-carrying coil – practical electronics:

https://www.ruselectronic.com/katushka-induktivnosti/

Then teacher:

      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 lesson.

Students would:

      Attempt the questions given by the teacher.

      Summarize the main concepts, definitions, and equations learnt.

      Reflect on their own learning.

      Evaluate their own work and the work of their classmates.

Extension Work:

      Complete the flipped reading and research assignment before the next lesson.

Homework:

      Complete the specified thinking tasks for this lesson.

      Should complete worksheet  given by teacher

 

Additional multilevel (on differentiation) tasks

The teacher  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

 

This 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 
(b) Electromagnet
(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.
Solenoid Behave like a magnet
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.
 
 
 
Discussion:
1. 
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.
2. 
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.
 
3. 
A thicker core might make a more powerful magnet. Just make certain that the material you choose can be magnetized. 
 
4. 
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.

 

 


 

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Theoretical material for the lesson, definitions for concepts

Theoretical material for the lesson, definitions for concepts

An electromechanical relay is a solenoid used to make or break mechanical contact between electrical leads

An electromechanical relay is a solenoid used to make or break mechanical contact between electrical leads

Learners will discuss their experiences with electromagnets

Learners will discuss their experiences with electromagnets

A permanent magnet is made of ferromagnetic material, which is magnetised by a strong external magnetic field

A permanent magnet is made of ferromagnetic material, which is magnetised by a strong external magnetic field

A thicker core might make a more powerful magnet

A thicker core might make a more powerful magnet
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