Magnetism and Electricity Class 8 Questions and Answers Notes Basic Science Chapter 11 Kerala Syllabus

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Class 8 Basic Science Chapter 11 Magnetism and Electricity Question Answer Notes

Class 8 Basic Science Chapter 11 Notes Kerala Syllabus Magnetism and Electricity Question Answer

Magnetism and Electricity Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
A student is trying to make a device to find direction using a magnetic needle. For this, he places the magnetic needle inside a box made of iron.
a) Will this device work properly?
b) Explain your answer.
c) What changes should be made to make this device work properly?
Answer:
a) No, the device will not work properly.

b) Iron is a magnetic material with high permeability. This means it allows the Earth’s magnetic field lines to pass through it very easily. The iron box will attract all the magnetic field lines, causing them to pass through the walls of the box instead of passing through the inside. The compass needle inside will be shielded from the Earth’s magnetic field and will not align to the North-South direction. This is called magnetic shielding.

c) The box should be made of a non-magnetic material (an insulator) that does not interfere with magnetic field lines. Examples: A box made of plastic, cardboard, wood, or aluminum.

Question 2.
AB is a bar magnet shown in the figure below. An iron rod CD is placed near its B pole.
• Which magnetic poles will be formed at the ends C and D?
• Which property of magnets does this phenomenon demonstrate?

Answer:
This is an example of Magnetic induction.

• The pole nearer to the magnet gets the opposite polarity.
• The pole farther from the magnet gets the same polarity.

Therefore:

• End C (nearer to B’s South pole) will become a North pole (N).
• End D (farther from B’s South pole) will become a South pole (S).

This phenomenon demonstrates Magnetic Induction. Magnetic Induction is the phenomenon where a magnetic substance acquires magnetism (Induced Magnetism) due to the presence of a magnet.

Question 3.
A bar magnet and a U magnet are shown in figures (a, b) each having two iron nails hanging from them.
a. Which is the correct figure in each case?
b. Explain the reason clearly.

Answer:
a.

• For the bar magnet: Figure A is correct.
• For the U-magnet: Figure B is correct.

b. Reason: The nails are magnetized by magnetic induction. When induced, the like poles (which form at the free ends of the nails) will repel each other.

In Figure A (Bar magnet): The magnet’s pole (e.g., North) induces an opposite pole (South) at the head of both nails and a like pole (North) at the tips. Since both tips are North poles, they repel each other and move apart.

In Figure B (U-magnet): The two poles of the U-magnet (N and S) are used. The nail on the N pole gets an S pole at its head and an N pole at its tip. The nail on the S pole gets an N pole at its head and an S pole at its tip. Since the free tips of the nails are now unlike poles (N and S), they will attract each other and move closer.

Question 4.
You are given a soft iron piece, a steel piece of the same size, insulated copper wire and a battery:
a. Suggest a method to make a powerful permanent magnet.
b. Suggest a method to make a temporary magnet.
Answer:
a. To make a permanent magnet, you must use the steel piece, which has high retentivity (the ability to retain magnetism).

• Method: Wrap the insulated copper wire around the steel piece many times to create a coil.
• Connect the ends of the wire to the battery and pass a strong electric current through it for some time.
• Even after the battery is disconnected, the steel will retain its magnetism.

b. To make a temporary magnet (an electromagnet), you must use the soft iron piece, which has high susceptibility (gets magnetized easily) but low retentivity (loses magnetism quickly).

• Method: Wrap the insulated copper wire around the soft iron piece.
• Connect the ends of the wire to the battery.
• The soft iron will become a strong magnet only as long as the electricity is flowing. It will lose its magnetism when the battery is disconnected.

Question 5.
In an experiment, a plastic car with an iron piece inside it, is made to run on a wooden table by sliding a strong magnet below it.
a) The experiment failed when a steel table was used. What is the reason for this?
b) If an aluminium table is used instead of steel, what will happen? Why?
Answer:
a) Reason: Magnetic Shielding.
Steel is a magnetic material (like iron). When the magnet is moved under the steel table, the steel table’s high permeability causes the magnetic field lines to pass through the table itself rather than passing above the table to reach the car. The steel table effectively shields the iron piece in the car from the magnet’s force, so the car does not move.

b) What will happen: The experiment will work.
Why: Aluminium is a non-magnetic material (like plastic or wood). It does not block or interfere with magnetic field lines. The magnetic field from the magnet will pass through the aluminium table easily and attract the iron piece in the car, making it move.

Basic Science Class 8 Chapter 11 Question Answer Kerala Syllabus

Textbook Page No : 186 & 187

Question 1.
Some situations in which magnets are used are given below. Add more situations.
Answer:

• MRI scanning machines
• Headphones and speakers
• Magnetic compass
• Electric motors
• Digital Compasses
• Electromagnets
• Maglev trains (Magnetic Levitation)

Question 2.
Some familiar magnets are given below. Complete the table.

Answer:

Textbook Page No : 188 & 189

Question 3.
What happens when the north pole of a magnet is brought near to the north Dole of another maanet?

observe the changes and complete the table.
Answer:

Activity	Observation
When the north poles are brought close to each other	Repels
When the north pole and the south pole are brought close to each other	Attracts
When the south poles are brought close to each other	Repels

Question 4.
Why is the pencil not falling down and floating in the air like this?
Answer:
The pencil is floating because of magnetic levitation. The magnetic force of repulsion between the magnets on the pencil and the magnets on the cardboard is strong enough to balance the force of gravity, causing the pencil to float in the air.

Question 5.
Can you move the pencil backward without touching it? How can it be possible?
Answer:
Yes, it’s possible. You can move the pencil by bringing another magnet near one of the floating magnets. If you bring a like pole (e.g., North pole to North pole), the repulsion will push the floating magnet and the pencil away.

Question 6.
What will happen if you bring another magnet near one side of the top magnet?
Answer:
It depends on which pole you bring close. If you bring a like pole near the top magnet, it will repel and move away. If you bring an unlike pole near it, it will attract and move towards the magnet you are holding.

Question 7.
Do you know if this special property of magnet is used in any technology?
Answer:
Maglev (Magnetic Levitation) Trains

Question 8.
What are Maglev trains?
Answer:
This is a major technology that uses magnetic levitation.

• Maglev trains are trains that run with out wheels.
• They use powerful electromagnets on the train and the track to repel each other.
• This levitates (suspends) the train above the track.
• Advantage: The absence of physical contact eliminates friction. This allows Maglev trains to reach extremely high speeds with minimal energy loss, and provides a quieter, smoother ride.

Textbook Page No : 190 & 191

Question 9.
When a bar magnet is suspended freely, in / which direction does it align?

Answer:
If a magnet can move freely, it always aligns in the north-south direction of the Earth.

Question 10.
Why does a magnetic compass always show the north-south direction?
Answer:
It is because of the influence of the Earth’s magnetic field. The Earth acts like a giant magnet with its own magnetic poles. The magnetic north pole of the Earth is near the geographic south pole, and the Earth’s magnetic south pole is near the geographic north pole.

Question 11.
How can we make an artificial magnet?
Answer:
You can make one by taking a magnetic material (like a hacksaw blade) and rubbing it with one pole of a strong magnet. You must rub it repeatedly in the same direction from one end to the other.

Textbook Page No : 192 & 193

Question 12.
How can you identify the poles of a ring magnet or a U-shaped magnet?
Answer:
You can use a magnetic compass (magnetic needle). If the north pole of the compass needle (often the red end) is repelled, that part of the magnet is a North pole. If the north pole of the compass is attracted, that part of the magnet is a South pole.

Question 13.
What is your conclusion after breaking a magnet into smaller pieces?
Answer:
No matter how small a magnet is, it will always have two poles (a north and a south pole). A magnet with only one pole (a monopole) does not exist.

Textbook Page No : 195 & 196

Question 14.
Is the distribution of magnetic field lines the same everywhere?
Answer:
No, the distribution of magnetic field lines is not the same everywhere around a magnet. The spacing of the lines indicates the strength of the magnetic field.

Question 15.
How is magnetic field strength related to magnetic field lines?
Answer:
The magnetic field is strongest where the magnetic field lines are closest together. These areas have a higher magnetic flux density.

Question 16.
What will happen to the magnetic flux if the size of the surface it passes through increases?
(Increase/ decrease)
Answer:
The magnetic flux will increase. Since magnetic flux is the total number of field lines passing perpendicular / normally through a surface, a larger surface will catch more lines.

Question 17.
Is the magnetic flux density higher at the poles of a magnet or at other places?
Answer:
The flux density is higher at the poles. The text states, “The poles of a magnet have the highest magnetic flux density.”

Question 18.
In the experiment with iron filings in a bottle (Fig 11.19), where do the filings stick the mo¬st and where do they stick the least?

Answer:
Most: The iron filings stick the most at the poles of the magnet.

Least: The filings are seen the least in the middle of the magnet, away from the poles. This happens because the magnetic field strength is greatest at the poles and gets weaker as you move away from them.

Textbook Page No : 197 & 198

Experiment (Fig. 11.20 & 11.21)

Question 19.
“Bring another pin near the free end of the first pin. Isn’t the second needle getting attracted?”
Answer:
Yes, the second pin gets attracted. This is because the first pin has become an induced magnet and can now attract other magnetic substances.

Question 20.
“Now, bring a magnetic compass near the free end of the needle. Isn’t the direction of the compass needle changing?”
Answer:
Yes, the direction of the compass needle changes. This confirms that the first pin has acquired Induced Magnetism and is acting as a magnet with defined poles.

Question 21.
“Then, carefully remove the first needle from the magnet. Does it still show magnetic properties? Write your observations in the science diary.”
Answer:
Observation: The first pin will still show some magnetic properties (attract paper clips or other pins) immediately after being removed, but this induced magnetism will be temporary and quickly weaken, depending on the material the pin is made of (e.g., iron or steel).

Question 22.
“What are the uses of magnetic induction? Discuss.”
Answer:

• Used in making electromagnets, where soft iron cores are induced to become temporary magnets.
• It is the principle by which a permanent magnet can attract non-magnetized magnetic objects (like iron nails).
• Used in magnetic separation techniques and the operation of certain electrical devices.

Question 23.
Which of these has greater susceptibility? (Soft iron/Steel)
Answer:
Soft iron.

Question 24.
Which of these has greater retentivity? (Soft iron/Steel)
Answer:
Steel

Textbook Page No : 199 & 200

Question 25.
Based on the characteristics you observed, which is more suitable for making strong temporary magnets, soft iron or steel?
Answer:
Soft iron is more suitable. Temporary magnets (electromagnets) need to acquire magnetism easily (high susceptibility) and lose it quickly (low retentivity) when the current or external field is removed.

Question 26.
When making permanent magnets, which magnetic property of steel should be utilised?
Answer:
The property of high retentivity should be utilised. Permanent magnets need to retain their magnetism for a long time.

Permeability and Experiment

Question 27.
What do you observe?
Answer:
Observation: When the iron filings are sprinkled and the plate is tapped, the filings will cluster around the magnets but will not stick to the area over the gap (the hole) in the large iron nut. The magnetic field lines are concentrated through the iron nut, bypassing the area where the air gap is.

Question 28.
Are the iron filings sticking to the area where the gap in the iron nut is present?
Answer:
No, the iron filings are not sticking to the area where the gap in the iron nut is present.

Question 29.
What conclusion do you reach?
Answer:
Conclusion: Soft iron (like the iron nut) has a higher ability than air to allow magnetic field lines to pass through it. The magnetic field lines prefer to travel through the path of least resistance, which is the soft iron, rather than the air gap.

Question 30.
Why do compass needles not show direction when placed inside a box made of soft iron?
Answer:
Explanation: Soft iron has very high permeability. When a compass is placed inside a soft iron box, the soft iron effectively diverts the Earth’s external magnetic field lines, causing them to pass through the box material instead of the air inside it. This magnetic shielding effect prevents the magnetic field from reaching the compass needle, so the needle cannot align itself with the Earth’s field and show direction.

Question 31.
Electromagnet Experiment; complete the table

Answer:

Experiment	Observation
When electricity flows, the soft iron piece and the paper clips	attracts
After removing the cell, the soft iron piece and the paper clips	does not attract

Question 32.
Based on this experiment, can you write down the different ways to increase the strength of an electromagnet?
Answer:

• Increasing the number of turns of the coil around the soft iron core.
• Increasing the current flowing through the coil (by increasing the number of cells/battery voltage).
• Increasing the cross-sectional area of the soft iron inside the coil.
• Using a core material with higher permeability (like soft iron).

Question 33.
Let’s write examples of devices that use electromagnets

Answer:

• Electric bells
• Loudspeakers
• Cranes (used to lift heavy iron objects)

Question 34.
What is the charge of the paint droplets?
Answer:

Electromagnets	Permanent Magnets
Poles can be changed	The gained magnetism can be retained for a long time
Magnetic strength can be changed/ varied (by changing the current or number of turns)	Magnetic strength cannot be increased

Class 8 Basic Science Chapter 11 Question Answer Extended Activities

Question 1.
What is the important role of neodymium magnets in electric vehicles (EVs)? How does the use of these magnets affect the vehicle’s efficiency, speed, and driving range? Collect information about this and prepare a report.
Answer:
Neodymium magnets are used to create permanent magnet synchronous motors (PMSM), which are highly efficient and powerful.

Efficiency: PMSMs with neodymium magnets are very efficient, converting a large percentage of electrical energy into mechanical energy.

Speed/Power: They allow for high power density, enabling faster acceleration and higher top speeds.

Driving Range: The high efficiency reduces energy consumption, leading to an extended driving range for the EV on a single charge.

Question 2.
Build a model of a vehicle that operates using magnetic levitation. Prepare a slide/chart explaining its working principle.
Answer:
This is a project-based activity involving building a model (e.g., a simple Maglev train model).

Working Principle (for the slide/chart): Magnetic levitation works using repulsive forces between magnets (either permanent magnets or electromagnets) to lift the vehicle above the track, eliminating friction. An electromotive force is then used to propel the vehicle forward.

Magnetism and Electricity Class 8 Notes

Class 8 Basic Science Magnetism and Electricity Notes Kerala Syllabus

Magnets are objects that can attract (ആകർഷിക്കുക) and repel (വികർഷിക്കുക) other objects. This property is called magnetism. Magnets are used in many devices.

Examples of Magnet Uses

• MRI scanning machines
• Headphones and speakers
• Magnetic compass
• Electric motors
• Maglev trains (Magnetic Levitation)

ആകർഷിക്കാനും വികർഷിക്കാനും കഴിവുള്ള വസ് തുക്കളാണ്. കാന്തങ്ങൾ. കാന്തിക ബലം ഉപയോഗി ച്ച് വസ്തുക്കളെ വായുവിൽ ഉയർത്തി നിർത്താൻ സാധിക്കും (Magnetic levitation).

Natural Magnets & Artificial Magnets

Natural Magnets (പ്രകൃതിദത്ത കാന്തങ്ങൾ)

• These are magnets that are obtained directly from nature.
• Example: Lodestone, Magnetite

Artificial Magnets (കൃത്രിമ കാന്തങ്ങൾ)

• These are magnets made by people in specific shapes, sizes, and strengths.
• They are typically made using metal alloys (ലോഹസങ്കരങ്ങൾ).

Types of Artificial Magnets
Artificial magnets are made from d materials.

• Alnico Magnets:
  These are alloys made from aluminum (Al), nickel (Ni), cobalt (Co), and iron (Fe).
• Ceramic/Ferrite Magnets
  These are made by mixing iron oxide with carbonates of elements like barium or strontium.
• Electromagnet
  This is a temporary magnet made by passing electricity through a wire coiled around a soft iron core.

General Properties of Magnets (കാന്തത്തിന്റെ പൊതുവായ സവിശേഷതകൾ)
1. Poles Exist in Pairs: Every magnet has two poles, a North pole (N) and a South pole (S). A magnet with only one pole (monopole) does not exist. If you break a magnet, each piece becomes a new, complete magnet (Each has two poles)
‘ഒരു കാന്തത്തെ എത്ര ചെറുതാക്കിയാലും, അതിന് എപ്പോഴും ഒരു ഉത്തരധ്രുവവും ദക്ഷിണധ്രുവവും ഉണ്ടായിരിക്കും. ഒരൊറ്റ ധ്രുവം (N or S) മാത്രമായി ഒരു കാന്തത്തിന് നിലനിൽക്കാൻ കഴിയില്ല.

2. Attraction & Repulsion: The fundamental law of magnetism is:

• Like poles repel ((സജാതീയ ധ്രുവങ്ങൾ വികർഷിക്കുന്നു.) (e.g., N-N or S-S).
• Unlike poles attract (വിജാതീയ ധ്രുവ ങ്ങൾ ആകർഷിക്കുന്നു) (e.g., N-S).

3. Directional Property: If a magnet is suspended freely (like being suspended by a string), it will always align itself with the Earth’s North-South direction.
ഒരു കാന്തത്തെ സ്വതന്ത്രമായി തൂക്കിയിട്ടാൽ, അത് എപ്പോഴും ഭൂമിയുടെ വടക്ക് തെക്ക് ദിശയിൽ വന്ന് നിൽക്കും. ഇതാണ് കാന്തത്തിന്റെ ദിശാസൂചക സ്വഭാവം.

Application: This is the working principle of a Magnetic Compass (വട ക്കുനോക്കിയന്ത്രം).).

• A compass is a device that uses this property.
• It contains a small magnetic needle that can rotate freely.
• This needle always points to the Earth’s North-South direction, allowing us to easily determine all other directions (East, West).

4. Magnetic Levitation: The repulsion of like poles can be used to make an object float, balancing the force of gravity (e.g., Maglev trains).

Maglev Trains

• This is a major technology that uses magnetic levitation.
• Maglev trains are trains that run without wheels.
• They use powerful electromagnets on the train and the track to repel each other.
• This levitates (suspends) the train above the track.
• Advantage: The absence of physical contact eliminates friction. This allows Maglev trains to reach extremely high speeds with minimal energy loss, and provides a quieter, smoother ride.

The Earth as a Giant Magnet (ഭൂമി ഒരു വൻകാന്തം)
The directional property of a compass works because the Earth itself acts like a big magnet, with its own magnetic field and poles.

• Cause of Earth’s Magnetism: This magnetic nature is believed to be caused by the movement of large amounts of molten iron and nickel in the Earth’s inner core.
• The “Pole-Swap”: The Earth’s magnetic poles are inverted compared to its geographic poles.
  1. The Earth’s Magnetic South Pole is located near the Geographic North Pole (the “top” of the world).
  2. The Earth’s Magnetic North Pole is located near the Geographic South Pole (the “bottom” of the world).
• How a Compass Works: A compass needle’s North pole is attracted to the Earth’s Magnetic South Pole (which is at our Geographic North). This is why a compass needle always points north!

ഭൂമി ഒരു വലിയ കാന്തമായി പ്രവർത്തിക്കുന്നു. ഭൂമിയുടെ കാന്തിക ദക്ഷിണ ധ്രുവം (Magnetic South Pole) അതിന്റെ ഭൂമിശാസ്ത്രപരമായ ഉത്ത ര ധ്രുവത്തിന് (Geographic North Pole) അടു ത്താണ്. ഒരു വടക്കുനോക്കിയന്ത്രത്തിലെ കാന്ത സൂചിയുടെ ഉത്തരധ്രുവം (N pole), ഭൂമിയുടെ ഈ കാന്തിക ദക്ഷിണ ധ്രുവത്താൽ ആകർഷിക്ക പ്പെടുന്നു. ഇതുകൊണ്ടാണ് കാന്തസൂചി എപ്പോഴും വടക്ക് ദിശയിലേക്ക് തിരിഞ്ഞുനിൽക്കുന്നത്.

Magnetisation (കാന്തവൽക്കരണം)
We can create artificial magnets using a process called magnetisation. One common way is the “single-touch” method.

Procedure (Fig. 11.12):

1. Place a hacksaw blade on a table.
2. Take a strong bar magnet. Using one pole (e.g., the North pole), rub the blade starting from one end (A) to the other end (B).
3. Lift the magnet and bring it back to end A.
4. Repeat this process several times, always rubbing in the same direction (A to B).

• Result: The hacksaw blade will become a magnet. The end where the rubbing starts (A) will become the North pole, and the end where the rubbing ends (B) will become the South pole.

• Observation (Fig. 11.13): When a magnet is broken into smaller pieces, each piece instantly becomes a new, complete magnet with its own North pole and South pole.
• Conclusion: “No matter how small a magnet is, it will always have two poles. A magnet with only one pole does not exist.” (These single poles are called ‘monopoles’).

ഒരു കാന്തത്തെ ഏത് ചെറിയ കഷണങ്ങളായി മുറിച്ചാലും, ആ ഓരോ കഷണവും ഒരു പൂർണ്ണ കാന്തമായിരിക്കും (അതിന് സ്വന്തമായി ഒരു നോ ർത്ത് പോളും സൗത്ത് പോളും ഉണ്ടാകും). ഒരു ധ്രുവം (Nor S) മാത്രമുള്ള ഒരു കാന്തത്തെ (magnetic monopole) നിർമ്മിക്കാൻ സാധ്യമല്ല.

Magnetic Field and Field Lines (കാന്തിക മണ്ഡലവും മണ്ഡലരേഖകളും)
Magnetic Field
The region around a magnet where its force can be felt is called the magnetic field.

Magnetic Field Lines (Fig. 11.16):

• Definition: These are imaginary lines used to represent the direction and strength of a magnetic field.
• Properties:
  1. They are closed loops.
  2. Outside the magnet, their direction is always from the North pole to the South pole.
  3. Where the lines are closer together (at the poles), the magnetic field is stronger.
• How to Draw Field Lines (Experiment):
  1. Place a bar magnet on a piece of paper.
  2. Place a magnetic compass near the North pole.
  3. Put a dot on the. paper where the north tip of the compass needle points.
  4. Move the compass so its south tip is at the dot you just made.
  5. Repeat this process, making new dots, until you reach the South pole.
  6. Connect the dots to draw a single magnetic field line.

ഒരു കാന്തത്തിന് ചുറ്റും അതിന്റെ ശക്തി (ആകർ ഷണ/വികർഷണ ബലം അനുഭവപ്പെടുന്ന മേഖല യാണ് കാന്തിക മണ്ഡലം (Magnetic Field), ഈ കാന്തിക മണ്ഡലത്തെ ചിത്രീകരിക്കാൻ ഉപയോഗി ക്കുന്ന സാങ്കൽപ്പിക രേഖകളാണ് കാന്തിക മണ്ഡല രേഖകൾ (Magnetic Field Lines). ഈ രേഖകൾ കാന്തത്തിന് പുറത്ത് എപ്പോഴും നോർത്ത് പോളിൽ നിന്ന് ആരംഭിച്ച് സൗത്ത് പോളിൽ അവസാനിക്കുന്നു.

Magnetic Field Strength and Magnetic Flux Density
These terms describe how strong a magnetic field is.

Magnetic Field Strenth

This is how strong the magnet’s influence is. The iron filing experiment (Fig. 11.19) shows that the magnetic field strength is greatest at the poles and gets weaker as you move away.

Magnetic Flux ((കാന്തിക ഫ്ളക്സ്))

• Definition: “The total number of magnetic field lines passing normally (perpendicularly) through a given surface”.

• If the size of the flat surface in Fig 11.18 increases, the magnetic flux passing through it will also increase.

Magnetic Flux Density (കാന്തിക ഫ്ളക്സ് ഡെൻസിറ്റി)

• Definition: “The number of magnetic field lines passing normal through a unit area…”.
• This is a measure of how concentrated or dense the field lines are.
• Key Relationship: Magnetic flux density is higher where the magnetic field strength is more. Since the field strength is greatest at the poles (where iron filings stick the most), the poles of a magnet have the highest magnetic flux density.
• മാഗ്നറ്റിക് ഫ്ളക്സ് ഒരു പ്രതലത്തിലൂടെ ലംബ മായി കടന്നുപോകുന്ന കാന്തിക മണ്ഡല രേഖക ളുടെ ആകെ എണ്ണമാണ് (Total number) ഫ്ളക്സ്.
• മാഗ്നറ്റിക് ഫ്ളക്സ് ഡെൻസിറ്റി: ഒരു നിശ്ചിത വിസ്തീർണ്ണത്തിൽ (Unit Area) എത്രമാത്രം മണ്ഡലരേഖകൾ ഉണ്ട് (അവയുടെ ‘തിക്ക്’. ‘അ ടുപ്പം’) എന്നതാണ് ഫ്ളക്സ് ഡെൻസിറ്റി.
• കാന്തത്തിന്റെ ശക്തി (Strength) ഏറ്റവും കൂടു തലുള്ളത് ധ്രുവങ്ങളിൽ (poles) ആണ്. ഇവിടെ കാന്തിക മണ്ഡലരേഖകൾ വളരെ അടുത്തടുത്താ ണ് സ്ഥിതിചെയ്യുന്നത്. അതിനാൽ, കാന്തിക ശ ക്തി എവിടെയാണോ കൂടുതൽ, അവിടെ ഫ്ളക് സ് ഡെൻസിറ്റിയും കൂടുതലായിരിക്കും.

Magnetic Induction (കാന്തിക പ്രവേശനം)

This is the phenomenon of making a temporary magnet without touching it.

• Definition: “The phenomenon of a magnetic substance (like an iron pin) acquiring magnetism due to the presence of a magnet is known as Magnetic Induction”.
• The magnetism the substance (pin) gets is called Induced Magnetism.

Polarity of Induced Magnetism:

• The polarity of the induced magnet is fixed:
  • Unlike polarity develops at the nearer end.
  • Like polarity develops at the farther end.
• Example (Fig 11.21): The permanent magnet’s North pole (N) is near the pin.

• • The head of the pin (nearer end) gets the unlike pole: South pole (S).
  • The tip of the pin (farther end) gets the like pole: North pole (N).

ഒരു കാന്തത്തിന്റെ സാന്നിധ്യം (presence) മൂലം മറ്റൊരു കാന്തിക വസ്തുവിന് (magnetic substance, e.g., ആണ്) താൽക്കാലികമായി കാന്തശ ക്തി ലഭിക്കുന്ന പ്രതിഭാസമാണ് മാഗ്നറ്റിക് ഇൻഡക്ഷൻ.

പ്രത്യേകത: കാന്തത്തിന്റെ ഏത് ധ്രുവമാണോ അടു ത്തു കൊണ്ടുവരുന്നത്, അതിന് വിപരീത ധ്രുവം (unlike pole) ആയിരിക്കും ആണിക്ക് അറ്റത്ത് ലഭി ക്കുക. ആണിക്ക് മറ്റേ അറ്റത്ത് കാന്തത്തിന്റെ അതേ ധ്രുവം (like pole) ആയിരിക്കും ലഭിക്കുക.

Properties of Magnetic Materials (Soft Iron & Steel)
Different materials react to magnetic fields differently.

• Experiment (Fig 11.22 & 11.23):

• Soft Iron (പച്ചിരുമ്പ്): Gets magnetized easily when placed near a magnet. But when the magnet is removed, it quickly loses its magnetism.
• Steel (ഉരുക്ക്): Takes more time to get magnetised. However, even after the magnet is removed, it does not lose its magnetism quickly.
  This leads to four important properties:

Susceptibility

• Definition: The ability of magnetic materials to get magnetised due to the influence of an external magnetic field.
• Soft Iron has greater susceptibility.

Retentivity

• Definition: The ability to retain the magnetism.
• Steel has greater retentivity.

Permeability

• Definition: The ability of a substance to pass magnetic field lines through it.
• Soft Iron has a high permeability.

Soft Iron VS Steel (പച്ചിരുമ്പും ഉരുക്കും)

Material	Susceptibility (പെട്ടെന്ന് കാന്തമാകും)	Retentivity (കാന്ത ശക്തി നിലനിർത്തും)	Use (ഉപയോഗം)
Soft Iron	High	Low	Temporary magnets (e.g., Electromagnets)
Steel	Low	High	Permanent magnets

Applications:

• Soft Iron is suitable for making temporary magnets (like electromagnets) because of its high susceptibility and low retentivity.
• Steel is suitable for making permanent magnets because of its high retentivity.
• Magnetic Shielding: A compass placed inside a soft iron box will not show direction because soft iron’s high permeability forces the Earth’s magnetic field lines to pass through the box rather than the in-side, shielding the compass.

Electromagnets വൈദ്യുതകാന്തങ്ങൾ

• Definition: A temporary magnet made by passing electricity through an insulated wire coiled around a soft iron core.
• Property: Only magnetic when the cur¬rent is on.
• Uses: Electric bells, loudspeakers, MRI machines.
• Increasing Strength: You can make an electromagnet stronger by:
  1. Increasing the number of turns in the coil (ചുറ്റുകളുടെ എണ്ണം കൂട്ടുക).
  2. Increasing the strength of the current (വൈദ്യുതിയുടെ ശക്തി കൂട്ടുക).
  3. Increasing the cross-sectional area of the soft iron core (പച്ചിരുമ്പിന്റെ കനം കൂട്ടുക).

ഒരു പച്ചിരുമ്പ് കോറിന് (soft iron core) ചുറ്റും കവചിത ചാലകം (insulated wire) ഉപയോഗിച്ച് വൈദ്യുതി കടത്തിവിടുമ്പോൾ നിർമ്മിക്കപ്പെടുന്ന താൽക്കാലിക കാന്തങ്ങളാണ് വൈദ്യുതകാന്തങ്ങൾ. വൈദ്യുതി നിലയ്ക്കുമ്പോൾ ഇവയുടെ കാന്തശ ക്തി നഷ്ടപ്പെടുന്നു.