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

The comprehensive approach in SCERT Class 8 Basic Science Textbook Solutions Chapter 11 Magnetism and Electricity Important Questions ensure conceptual clarity.

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

Magnetism and Electricity Class 8 Important Questions

Question 1.
Which material is most suitable for making a permanent magnet?
a) Soft Iron
b) Steel
c) Copper
d) Lodestone
Answer:
b) Steel. (It is used for permanent magnets due to its high retentivity).

Question 2.
The phenomenon of an object floating in the air using magnetic force to balance gravity is called:
a) Magnetic Induction
b) Magnetic Levitation
c) Magnetisation
d) Magnetic Permeability
Answer:
(b) Magnetic Levitation.

Question 3.
The ability of a magnetic material to get magnetized due to an external magnetic field is called:
a) Susceptibility
b) Permeability
c) Retentivity
d) Induction
Answer:
a) Susceptibility.

Question 4.
Statement 1: When a magnet is broken into two pieces, one piece will be a North pole and the other will be a South pole.
Statement 2: A freely suspended magnet aligns in the North-South direction because the Earth itself acts like a giant magnet.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
c) Only Statement 2 is correct. (Statement 1 is incorrect; each piece will be a new, complete magnet with both a North and South pole).

Question 5.
Statement 1: Magnetic field lines outside a magnet are directed from the South pole to the North pole. Statement 2: The magnetic field strength is greatest at the poles of a magnet.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
c) Only Statement 2 is correct. (Statement 1 is incorrect; they are directed from the North pole to the South pole).

Question 6.
Statement 1: Soft iron is used to make the core of an electromagnet because it has low retentivity and high susceptibility.
Statement 2: Steel is used to make permanent magnets because it has high retentivity.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
a) Both statements are correct.

Question 7.
Classify the following materials based on their primary use in magnetism (Permanent Magnet / Temporary Magnet):
(Soft Iron, Alnico, Steel, The core of an electric bell)
Answer:
Permanent Magnet: Alnico, Steel
Temporary Magnet: Soft Iron, The core of an electric bell (which is an electromagnet)

Question 8.
Categorize the following as Natural Magnets or Artificial Magnets: (Lodestone, Bar magnet, Electromagnet, Horseshoe magnet. Ceramic magnet)
Answer:
Natural Magnets: Lodestone
Artificial Magnets: Bar magnet, Electromagnet, Horseshoe magnet, Ceramic magnet

Question 9.
Find and correct the error in this statement:
“A magnetic compass needle points to the Earth’s Geographic North Pole because it is attracted to the Earth’s Magnetic North Pole.”
Answer:
Error: It is attracted to the Earth’s Magnetic North Pole.

Correction: A magnetic compass needle points to the Earth’s Geographic North Pole because its North pole is attracted to the Earth’s Magnetic South Pole, which is located near the Geographic North Pole.

Question 10.
Find and correct the error in this statement:
“To make a permanent magnet, I will wrap an insulated wire around a soft iron rod and connect it to a battery.”
Answer:
Error: Using a soft iron rod.
Correction: To make a permanent magnet, you should wrap the wire around a steel rod, not soft iron. (Soft iron would create a temporary electromagnet

Question 11.
Find and correct the error in this statement:
“Magnetic field lines are imaginary lines that show the direction of magnetic force. They start at the South pole and end at the North pole.”
Answer:
Error: They start at the South pole and end at the North pole.
Correction: Outside the magnet, magnetic field lines are directed from the North pole to the South pole.

Question 12.
Why is repulsion, and not attraction, considered the sure test for magnetism?
Answer:
Repulsion only occurs between two like poles (N-N or S-S) of magnets. Attraction, however, can occur in two different situations:

1. Between two unlike poles (N-S).
2. Between a magnet and an unmagnetized magnetic substance (like an iron nail) due to magnetic induction. Since attraction is not unique to two magnets, only repulsion can definitively prove that both objects are magnets.

Question 13.
Why will a freely suspended bar magnet always align itself in a North-South direction?
Answer:
This happens because the Earth itself acts like a giant magnet, with its own magnetic poles and magnetic field. The North pole of the bar magnet is attracted to the Earth’s Magnetic South Pole (which is located near the Geographic North Pole), and the magnet’s South pole is attracted to the Earth’s Magnetic North Pole. This alignment guides the magnet.

Question 14.
If you place a magnetic compass inside a box made of soft iron, it will not show the correct North-South direction. Why?
Answer:
This is due to magnetic shielding. Soft iron has a very high permeability, meaning it allows magnetic field lines to pass through it very easily. The soft iron box will “absorb” the Earth’s magnetic field lines, guiding them through its walls. This prevents the field lines from reaching the compass needle inside, so the needle cannot align with the Earth’s magnetic field.

Question 15.
A bar magnet (AB) with pole A as North and pole B as South is placed near an iron rod (CD) as shown in the assessment question.
a) What magnetic pole is induced at end C?
b) What magnetic pole is induced at end D?
c) What is this phenomenon called?
Answer:
a) The pole B (South) is near end C.
By induction, the nearer end gets the opposite pole. Therefore, C be comes a North pole.
b) The farther end D gets the like pole. Therefore, D becomes a South pole.
c) This phenomenon is called Magnetic Induction

Question 16.
You are given two identical-looking steel bars. One is a permanent magnet, and the other is just a plain steel bar. How can you identify which is the magnet without using any other object (like a compass or a third bar)?
Answer:

1. Hold one bar (Bar A) in your hand.
2. Bring one end of the second bar (Bar B) and touch it to the center of Bar A. Note the force.
3. Now, touch the same end of Bar B to one of the ends of Bar A.
4. Repeat this by trying to pick up Bar B with Bar A.
5. Observation: A magnet’s strength is strongest at the poles and very weak (almost zero) at its center. The unmagnetized steel bar has uniform properties.
6. Conclusion: The bar that can attract the other bar at its ends but cannot attract it (or attracts very weakly) at its center is the permanent magnet. The other bar is the plain steel bar.

Question 17.
You are given a hacksaw blade, a strong bar magnet, and some iron filings. Describe the procedure to:
a) Magnetise the hacksaw blade.
b) Confirm that the blade has been magnetized and identify its poles.
Answer:
a) Magnetisation (Single-Touch Method):

1. Place the hacksaw blade flat on a table.
2. Take the bar magnet and pick one pole (e.g., the North pole).
3. Press this pole down at one end of the blade (End A).
4. Rub the magnet along the blade to the other end (End B) in one continuous stroke.
5. Lift the magnet and bring it back to End A.
6. Repeat this process 20-30 times, always moving in the same direction (A to B) and using the same pole.

b) Confirmation:

1. Dip the newly magnetized blade into the pile of iron filings.
2. If it is magnetized, the iron filings will stick to it, especially at the ends (poles).
3. (To identify poles, you would need a compass or a known magnet, as the filings only show the presence of poles, not their N/S identity).

Question 18.
Describe an experiment to make a simple electromagnet and test its properties.
Answer:
Experiment:
Making: Take a soft iron nail and a long piece of insulated copper wire. Wind the wire tightly around the nail many times to form a coil.
Testing (OIM): Connect the free ends of the wire to the terminals of a battery. Bring the tip of the nail near a pile of paper clips.
Observation 1: The nail attracts the paper clips, proving it is now a magnet.
Testing (OFF): Disconnect one end of the wire from the battery.
Observation 2: The paper clips fall off the nail.
Conclusion: This shows that a mag¬net can be created with electricity, and it is a temporary magnet (an electromagnet) that only works when current is flowing.

Question 19.
Describe a procedure to draw the magnetic field lines of a bar magnet using a magnetic compass and a piece of paper.
Answer:

1. Place a white paper on a flat surface and fix it.
2. Place a bar magnet at the center of the paper and trace its outline. Mark the N and S poles.
3. Place a magnetic compass near the North pole (N).
4. Put a small dot on the paper at the exact point where the north tip of the compass needle is pointing.
5. Move the compass so that its south tip is now at the dot you just marked.
6. Put a new dot where the north tip is pointing now.
7. Repeat this “dot-to-dot” process. The compass will trace a curved path.
8. Continue until you reach the South pole (S) of the magnet.
9. Join all the dots to form a smooth curve. This is one magnetic field line.
10. Add an arrow to this line, pointing from North to South, to show its direction.
11. Repeat the entire process starting from a different point near the North pole to draw more field lines.

Question 20.
Name the following magnet.

Answer:
Bar magnet, Magnetic needle, U mag-net, Ring magnet, disc Meignetic

Question 21.
Which instrument is used to identify the direction in ship journey in ancient time?
Answer:
Compass

Question 22.
A bar magnet is hanged by a thread. Where does the north pole of the magnet point?
Answer:
The north pole of the compass points towards north of the earth that is south pole of earth’s magnet because earth is a magnet.

Question 23.
Write the magnetic substances from the following.
Wooden block, iron nail, paper, nickel, gold, cobalt, aluminium
Answer:
Iron nail, nickel, cobalt

Question 24.
Write the right statement
Greater susceptibility (Soft iron/ Steel)
Greater retentivity? (Soft iron/Steel)
Answer:
a. Soft iron b. Steel

Question 25.
Write three method to increase the strength of an electromagnet.
Answer:

1. The number of turns of coiled conductor
2. the strength of current
3. the area of cross section of the soft iron placed inside the coil.

Question 26.
You are given a bar magnet. The poles are not marked on it. Suggest a method to identify the poles of the magnet.
Answer:
The magnet is suspended using a thread so that it can oscillate freely in a horizontal plane. When it comes to rest the end pointing south can be marked as south pole.

Question 27.
A magnet is dipped in iron filing, the iron fillings are more attracted towards the poles of the magnet than towards other places. Why?
Answer:
The intensity at the poles is greater than that at other places.

Question 28.
North of geomagnet inclined against 110 with geoscientific north pole? Examine the statement.
Answer:
The statement is incorrect. North of geomagnet inclined against 11o with geoscienfic south pole. Magnet suspended on geomagnet alinged south – north direction is due to the attraction of unlike poles. North pole (N) of magnet attracted towards the south pole of geomagnet.

Question 29.
What are the difference in the magnetic properties of iron and steel?
Answer:
Iron becomes a more intense magnet on magnetic induction. But that magnetic power is temporary. When the permanent magnet is removed it losses its magnetic power. In the presence of a magnet, steel doesn’t acquire the magnetic power like that of a soft iron. But steel retains most of its magnetic power after removing the permanent magnet.

Question 30.
Write your inferences.
a. All magnets have same shape.
b. All magnets show N, S direction when suspended freely.
c. All magnets are man made.
d. All magnets show N, S direction when suspended freely.
Answer:
a. No, There are different types of magnets.
b. Yes, Because the north pole of magnet turns to geographical south of earth and south pole turns to geographical north of earth.
c. No, There are natural and man made magnets.
d. Yes.Earth acts like a large magnet. Hence the poles of the suspended magnet is opposite to the poles of the earth’s magnet.

Question 31.
When an iron nail is wounded with copper wire and connected to a battery, it doesn’t become a magnet, select the reasons from the following.
a. Battery has not enough charge.
b. The insulation at the ends of the wire is not removed.
c. The nail is wounded with non insulated copper wire.
d. The polarity of the battery is changing.
Answer:
a. Battery has not enough charge, b. The insulation at the ends of the wire is not removed, c. The nail is wounded with non insulated copper wire.

Question 32.
An Iron nail is suspended at the north pole of a bar magnet. Bring the north pole of another magnet near the free end of a nail. What is observed? What is its reason?
Answer:
The free end of an iron nail repel. Because the free end of an iron nail becomes north pole by magnetic induction.

Question 33.
Complete the figure

Answer:

Question 34.
The pole of a magnet attracts an iron nail which has no magnetic power. Describe the working behind this.
Answer:
The magnet attracts the iron nail brought near the pole of a magnet really as the result of magnetic induction. If the magnetic material reaches near the magnetic field of the magnet, an unlike pole is induced at its near end. The pole of permanent magnet is attract the newly formed unlike poles. That is why the magnetic pole attracts a magnetic material near it.

Question 35.
What are the factors that the attractive force of two magnetic poles depend on?
Answer:
The attractive force between the magnetic poles increases with increase in the strength of the pole and decreases with increase in the distance between the poles.

Question 36.
What is meant by atomic magnets?
Answer:
Each atom of a magnetic substance is an independent magnet. They are called atomic magnets.

Question 37.
What is meant by line of force (line of flux)?
Answer:
The line of force is the path that the north pole of a free magnetic needle would take around the bar magnet.

Question 38.
Examine the figure and mark the poles

Answer:

Question 39.
Which among the following statements is correct?
a) Like poles attracts each other.
b) Magnetic field is experienced in all directions around a magnet.
c) The direction of magnetic lines of force is from the north pole outside the magnet.
Answer:
b)Magnetic field is experienced in all directions around a magnet.

Question 40.
In the figure, south poles of two bar magnets are placed facing one another. Redraw the figure and illustrate magnetic field lines?

Answer:

Question 41.
Which of the following has more susceptibility.”(Steel / Soft iron)
Answer:
Soft iron

Question 42.
The following figures depict, two electromagnets made from two iron nails of same size. Which is the strongest electromagnet?

Answer:
a)

Question 43.
a) Draw magnetic lines of force between the given poles of magnets.

b) Write any two peculiarities of magnetic lines of force.
Answer:
a)

b) i. Magnetic lines of force do not intersect one other
ii. Magnetic lines of a force are from north pole to south pole

Question 44.
A magnetic needle is suspended so as to move freely in a horizontal plane.
a. In which direction north pole of the magnetic needle is pointing.
b. Give reason for it.
c. The case of magnetic compass is not made of soft iron? Why?
Answer:
a. The north pole of a bar magnet pointing towards the geographic north when it suspended freely.

b. The earth itself acts like a magnet. Just as the earth has north and south geographically the earth has north and south geographically. It has the north pole and the south pole when considered as a magnet. The south pole of the earth’s magnet is near the geographic north and the north pole of the earth’s magnet is near the geographic south. Hence the freely suspended magnet pointing towards the geographic north.

c. Magnetic lines of force pass more easily through soft iron than through the air. This ability is called as permeability. Hence the magnetic lines of forces from the magnetic needle spread into the iron case and the needle loses its directional property. So the case of magnetic compass is not made of soft iron core.

Question 45.
Select the correct statement.
a. The north pole of the earth’s magnet is near the geographic north pole.
b. The south pole of the earth’s magnet is near the geographic north pole.
c. The south pole of the earth’s magnet is at the equator.
Answer:
b.The south pole of the earth’s magnet is near the geographic north pole.

Question 46.
A magnetised hacksaw blade is cut into pieces as shown in figure.

a. Find the polarity of the edges B and D.
b. Suggest a method to make the hacksaw blade into a permanent magnet.
Answer:
a. B-North D – North

b. Place the hacksaw blade on a table. Rub the north pole of the bar mag-net NS starting from one end to the another end of the blade. Repeat it several times in the same manner. The hacksaw blade will change into a magnet.

Question 47.
An iron rod and a steel rod of equal size are placed near a magnet. Complete the following table based on the property of these substances.

Which rod act as a stronger magnet	…………… a …………..
Which rod retains the magnetic powder even after removed it from the magnet	…………… b …………..

Answer:
a. Iron rod
b. Steel rod

Question 48.
A and B are two magnetic materials. Analyse their properties and answer the questions.
i. A is easily magnetised compared to B than that for A.
ii. Ability to retain the magnetism thus acquired is more for B than that for A
a. Which these is the most suitable material for making a permanent magnet? Explain why?
b. Write the name of a substance used for making permanent magnets.
Answer:
a. B is the suitable material used to make permanent magnet. Because it has retentivity or it has the ability retain the acquired magnetic strength.

b. Steel, Alnico

Question 49.
The magnetic flux lines between two
magnetic poles are drawn in the figure.

a. Name the poles represented by A and B.
A. ……………………… B. …………………………….
b. Give the principle helped you to write down this answer
Answer:
a. A – South, B – North
b. The direction of magnetic lines of force is from the north pole to the south pole.

Question 50.
Which of the following is the correct picture?

Answer:
c

Question 51.
a. Which are the materials required to make an electromagnet
b. Using these materials, how can you make an electromagnet?
c. Suggest a method to increase the strength of an electromagnet?
Answer:
a. Insulated copper wire, soft iron piece.
b. By passing electric current through insulated copper wire wound on a so¬ft iron piece.
c. By increasing the number of turns of wire in the coil

Question 52.
Which of the following is an example of a natural magnet?
A. Alnico magnet
B. Horseshoe magnet
C. Lodestone
D. Electromagnet
Answer:
C. Lodestone

Question 53.
What is the directional property of a freely suspended magnet?
A. It aligns itself East-West.
B. It aligns itself North-South.
C. It points towards the nearest metal object.
D. It always points towards the sun.
Answer:
B. It aligns itself North-South.

Question 54.
Which pair of magnetic poles will exhibit the strongest force of repulsion?
A. North pole (N) and South pole (S)
B. North pole (N) and North pole (N)
C. South pole (S) and South pole (S)
D. Both B and C
Answer:
D. Both B and C

Question 55.
Where is the Earth’s Magnetic South Pole located?
A. Exactly at the Geographic South Pole.
B. Near the Geographic South Pole.
C. Near the Geographic North Pole.
D. Exactly at the Equator.
Answer:
C. Near the Geographic North Pole.

Question 56.
What does the high density of magnetic field lines in a specific region indicate?
A. The magnetic field is weakest in that region.
B. The region is non-magnetic.
C. The magnetic field is strongest in that region.
D. The magnetic field lines are intersecting.
Answer:
C. The magnetic field is strongest in that region.

Question 57.
Explain the rule for attraction and repulsion between magnetic poles. Give one application of this principle.
Answer:
Rule for Attraction and Repulsion:
Attraction: Unlike poles attract each other (North attracts South).
Repulsion: Like poles repel each other (North repels North, and South repels South).
Application: This principle is used in Magnetic Levitation (Maglev) technology, where the repulsion between like poles is used to lift a train above the track, eliminating friction.

Question 58.
Describe the composition of two types of artificial magnets mentioned in the chapter.
Answer:
Composition of Artificial Magnets: Alnico Magnets: These are strong metal alloys made from Aluminum, Nickel, Cobalt, and Iron (Fe).
Ceramic/Ferrite Magnets: These are made by mixing iron oxide with carbonates of elements like barium or strontium.

Question 59.
State two essential characteristics of magnetic field lines. How does the “SingleTouch Method” of magnetisation work, and what pole is acquired at the starting end of the unmagnetised material?
Answer:
Characteristics of Magnetic Field Lines:

• Closed Loops: Magnetic field lines form continuous, closed loops. They emerge from the North pole and enter the South pole outside the magnet, and continue from South to North inside the magnet.
• Non-Intersecting: They never intersect (cross) each other. If they did, it would mean that at the point of intersection, a compass needle would point in two different directions simultaneously, which is impossible.
• (Note: Stating the direction (N to S outside the magnet) is also a valid characteristic.)
• Single-Touch Method and Pole Acquisition:
• The Single-Touch Method involves repeatedly stroking an unmagnetised material (like a steel bar) in a single, consistent direction using one pole of a permanent magnet.
• The pole acquired at the starting end of the steel bar will be the opposite pole to the one used for rubbing. For example, if you rub the bar starting from end A using a North pole, end A will acquire a South pole.

Question 60.
What is a magnetic field, and where is the field strength typically the strongest on a bar magnet?
Answer:
A magnetic field is the region of space surrounding a magnet where its magnetic force can be experienced by another magnetic material or magnet. The magnetic field strength is typically the strongest at the poles (the North and South ends) of the bar mag¬net, where the magnetic field lines are densest.

Question 61.
Explain the difference between natural and artificial magnets, and give one example for each type, including the specific composition for the artificial magnet example.
Answer:
Natural Magnets
Definition: Magnets that are obtained directly from nature.
Purpose: Used as they are found. Example: Lodestone (mineral name: Magnetite).
Artificial Magnets
Definition: Magnets that are man-made using various metallic alloys.
Purpose: Made in specific shapes, sizes, and strengths as needed by humans.
Example: Alnico Magnets: These are alloys primarily made from Aluminum (Al), Nickel (Ni), Cobalt (Co), and Iron (Fe).