Magnetism of iron and steel

Experiment 1: Experimental setup as shown in Fig

Experiment 1. (Photo: Internet Collection)

Close switch K to allow current to flow through the coil. Observe the angle of deviation of the magnet needle from the original direction

Place the wrought iron or steel core in the inner tube. Close switch K. Observe and comment on the deflection angle of the magnet needle compared to the case of a wire tube without iron (steel) core.

Conclusion of experiment 1:

Lock K is closed, the magnet needle is deviated from the original direction.

Put the iron (steel) core inside the coil, the deflection angle of the magnet needle is larger than the case without the iron (steel) core.

⇒ Comment: The iron or steel core increases the magnetic effect of the current-carrying wire.

Experiment 2: Experiment set up as shown in Fig

Experiment 2. (Photo: Internet Collection)

Indicate the phenomenon that occurs with iron nails in the case of:

The pipe with a young iron core is sucking the nail. Disconnect the KEEP switch

The pipe with a steel core is sucking the nail. Disconnect the KEEP switch

Conclusion of experiment 2: When the current through the wire is cut off, the young iron core does not attract the nail while the steel core still attracts the nail.

⇒ Comment: The young iron core loses all its magnetism, while the steel core retains its magnetism

After conducting 2 experiments, we draw the general conclusion:

The iron or steel core increases the magnetic effect of the current-carrying wire.

When the power is turned off, the young iron core loses all its magnetism and the steel core remains magnetic.

Compare the magnetization of iron and steel

After the above 2 experiments, students can draw different characteristics about the magnetization of iron and steel:

Iron and steel both have the ability to increase the current of the coil.

Iron is more strongly magnetized than steel but demagnetized immediately.

Steel is less magnetized than steel but retains its magnetism longer.

Conclusion: Because of the above reasons, people will apply the magnetization of steel to make permanent magnets. As for iron, people will use it to make electromagnets.

What is an electromagnet?

Next we will learn more about the definition, structure, operating principle and practical application of an electromagnet.

What is an electromagnet?

An electromagnet is a material that generates a magnetic field or in other words, it is a source of magnetic field generation.

Electromagnets work thanks to the magnetic field generated by the coil with a large current flowing through it. When current stops flowing, the electromagnet loses its magnetism.

The birth of the electromagnet: In 1825, the electromagnet was invented under the research of scientist William Sturgeon (1783-1850). Scientist Sturgeon’s electromagnet was originally a young iron core similar in shape to a horseshoe. Besides, the iron core will be wrapped around by the wire loop. When the current generated by the small battery flows through, the iron core becomes magnetized and produces a magnetic induction strong enough to be able to attract a 7-ounce iron can. His invention is considered to be the primitive foundation for the birth of modern devices later.

Although scientist Sturgeon was the first to develop the electromagnet, the person who improved this invention was the physicist Joseph Henry. Besides improving the attraction of electromagnets, he also invented other machines such as telephones, telegraphs and electric motors.

The birth of the electromagnet. (Photo: Internet Collection)

Compared with permanent magnets, electromagnets have a number of outstanding advantages such as:

Can generate a magnetic field much stronger than a permanent magnet

It is possible to completely demagnetize a magnet simply by interrupting the current flowing through it

The strength of the magnet can be adjusted by changing the number of turns or increasing or decreasing the current flowing through the coil.

Structure & working principle of electromagnet

Structure of an electromagnet. (Photo: Internet Collection)

Construction of electromagnet

The structure of an electromagnet consists of:

A long electric wire is wound around a young iron core, the wire is made of copper metal. As a result, when a current flows through that coil, the coil will become strongly magnetic inside.

On the other hand, thanks to the magnetization accumulated in the iron core, the magnetism also becomes stronger because of that. However, as long as we cut off the current, the iron core will lose its magnetism immediately.

The core of the electromagnet is made of wrought iron.

People use wrought iron instead of steel because if steel is used, when cutting the current flowing through the wire, the steel core will still retain its magnetism and still be able to attract metal.

At that time, the electromagnet will become a permanent magnet, not meeting production needs.

Working principle of electromagnet

Working principle of electromagnet. (Photo: Internet Collection)

Electromagnets work on the principle of electromagnetic induction.

When conducting current to the coil wound many times around the ferromagnetic core, the current will produce an electric field E inside the windings that is capable of attracting magnetic metal.

A magnetic field B perpendicular to the electric field E will be generated as a result of the action of the electromagnetic field.

When we disconnect the current, this magnetic field will disappear completely, and only when the current is restored will the coil act like an electromagnet. The magnetic field of the coil will depend on the current in the coil and the number of inductances.

The coil inductance is directly proportional to the number of turns, length and inversely proportional to the area of that winding.

When you put any steel core or iron core into a wire tube and let the current flow through the wire, the steel core (iron) will become magnetic and become a magnet, along with which will increase the magnetic effect of the tube. wire.

How to increase the magnetic force of an electromagnet?

To better understand how to increase the magnetic force of the electromagnet, we need to determine the factors that affect the magnetic force of the electromagnet. First of all, the magnetic field of the conducting coil depends on two factors that are the number of inductance of the coil and the amount of current flowing in the coil.

In which, the number of inductance of the coil will be proportional to the number of turns of the coil and inversely proportional to the area of that coil.

Based on those factors, we can determine two ways to increase the magnetic force of an electromagnet acting on an object as follows:

Increase the amount of current flowing through the loops of wire.

Increase the number of turns of wire wrapped around the coil.

Applications of electromagnets

Electromagnets are widely used in daily life. Industries that use electromagnets include transportation, healthcare, industry, electronics, etc.

• In the industry

Electromagnets help lift heavy objects. (Photo: Internet Collection)

Nowadays, electromagnets are widely used. Typically in the iron and steel processing process, using electromagnets in iron recycling or at major shipping and seaports,… Products manufactured from electromagnets include: electric pickup trucks , electric motors, microphones, loudspeakers, sensors, traveling wave tubes, sensors, clocks, microwave equipment, automatic control devices, aeronautical engineering, spaceflight, etc.

Most of the magnets used in industry are large magnets with strong magnetic attraction and great lifting power compared to ordinary magnets. The purpose of using electromagnets is to transport and support heavy metals during production and construction.

• In the medical industry

Electromagnets are used a lot in MRI diagnostic techniques to diagnose and detect diseases and cancer cells for patients.

This is considered one of the important applications of electromagnets because it is an extremely modern magnetic resonance imaging technique, using magnetic fields and radio waves to effectively solve health problems in the body. patient’s body without the need for invasive surgery.

• In the transportation industry

Electromagnets used in electric trains. (Photo: Internet Collection)

Electromagnets are also used in transportation, typically subway manufacturing applications. Thanks to the magnetic properties of electromagnets, people have found a way to accelerate the speed of the train, helping the train to move quickly and easily.

• In daily life

Besides, we can also easily see the appearance of electromagnets in daily life, through close and common objects such as automatic teller machines, credit cards, television screens. , parts of loudspeakers, television stations or moving vehicles such as electric motorcycles, electric bicycles, …

Exercise magnetization of iron and steel electromagnets

Lesson 1: An electromagnet consists of a coil of wire wrapped around a young iron core with current flowing through:

a) If the current is cut off, will it still have magnetic effect?

b) The core of the electromagnet must be wrought iron, not steel. Why?

The answer:

a) If the current is cut off, the electromagnet will no longer have a magnetic effect.

b) Because the steel wire still retains its magnetism when the power is cut off. Then the electromagnet loses its use.

Lesson 2: In the electromagnet drawn in Figure 25.1 SBT, if the young iron core is replaced by a nickel core, then:

a) Is the magnetic field stronger than a coil without a core?

b) What is the terminal A of the coil?

The answer:

a) The magnetic field is stronger. Because nickel has a strong magnetism like steel.

b) Applying the rule of holding the right hand, we get the end of A as the North pole.

Lesson 3: Figure 25.2 shows some iron paper clips that are attracted to the poles of the bar magnet.

a) Can these iron clamps become magnets? Why?

b) If it is confirmed that the iron clamps have become magnets, identify the magnetic pole name of one of these magnets.

c) From the above results, explain why magnets attract iron and steel objects when placed near it.

The answer:

Apply theory:

When the magnetic poles of two bar magnets are brought together, they attract each other if the poles have different names, repel each other if the poles have the same name.

When iron is placed in a magnetic field, the iron becomes magnetized.

a) Since the iron clamps placed in the magnetic field of the magnet are magnetized, it can be confirmed that it has become a magnet.

b) The names of the magnetic poles of some iron clamps are shown in Figure 25.1.

c) When placing iron or steel objects near a magnet, the object becomes magnetized and becomes a magnet. The tip placed near the magnet is the opposite magnetic pole of the magnet. Hence being attracted to the magnet.

Lesson 4: In the following cases, in which cases can objects become magnetized and become permanent magnets?

A. A steel wire loop is briefly brought close to one pole of a strong electromagnet, and then away.

B. A ring of wrought iron wire is brought close to one pole of a strong electromagnet for a short time, and then away.

C. A ring of wrought iron wire is brought close to one end of a strong electromagnet for a long time, and then away.

D. A young iron core is placed in the heart of a coil with a large current for a long time, and then moved away.

Answer: Answer A.

Detailed explanation: Because after being magnetized, young iron does not retain its magnetism for a long time, and steel retains its magnetism for a long time, so the case where an object is able to magnetize and become a permanent magnet is a steel conductor ring. brought close to one pole of a strong electromagnet for a short time, and then away. (Apply the theory: After being magnetized with young iron, which does not retain its magnetism for a long time, the steel retains its magnetism for a long time.)

Lesson 5: What happens to a steel bar when it is placed inside a wire with direct current flowing through it?

A. The steel bar is heated up.

B. The steel bar is glowing.

C. The steel rod is pushed out of the pipe.

D. The steel bar becomes a magnet.

Answer: EASY Answer

Detailed explanation: There is a magnetic field inside a wire with a direct current flowing through it. When the steel bar is put in, the steel bar will become magnetized and become a magnet. (Apply the theory: Magnetic materials placed in a magnetic field are magnetized.)

Lesson 6: When a young iron rod is placed in the heart of a conduit with direct current flowing through, the iron bar becomes a magnet. The north-south direction of a newly formed magnet relative to the north-south direction of the coil is:

A. Same direction.

B. Reverse direction.

C. Perpendicular.

D. Form a 450 angle.

Solution: Answer A

Detailed explanation: When a young iron rod is placed in the heart of a conductor with direct current flowing through it, the iron bar becomes a magnet. The north-south direction of a newly formed magnet is in the same direction as the north-south direction of the spool.

Lesson 7: Is there a way to increase the magnetic force of an electromagnet?

A. Use a large wire to wrap a few turns.

B. Use a small wire to wrap many turns.

C. Increase the number of turns of the conductor and decrease the voltage applied to the two ends of the conduit.

D. Increase the diameter and length of the conduit.

Answer: ANSWER

Detailed explanation: In the above ways to increase the magnetic force of an electromagnet, we use a small wire wound many times. (Apply the theory: To increase the magnetic force of the electromagnet, we increase the current flowing through the turns of the wire or increase the number of turns of the coil.)

Lesson 8: Why is the core of an electromagnet not made of steel but made of wrought iron?

A. Because the magnetized steel core is weaker than the young iron core.

B. Because of using a steel core, after being magnetized, it will turn into a permanent magnet.

C. Because using a steel core, it is not possible to change the strength of the electromagnetic force of the electromagnet.

D. Because the steel core is used, the magnetic force is reduced compared to when there is no core.

Answer: ANSWER

Epilogue

Above are the necessary knowledge for the process of learning and learning about the magnetization of iron and steel – Electromagnets. Hopefully with the information that Monkey has provided, they can learn effectively by themselves as well as improve their own understanding.