Goyal Brothers Solutions for ICSE Class 9 Physics Chapter 11 Electricity And Magnetism 2

Exercise

(A) Objective Questions

Question. A bar magnet is rubbed on a bar of steel along its length 20 times. The bar of steel gets magnetised due to the process of :
(a) induction
(b) conduction
(c) friction
(d) none of the these
Answer: (b) conduction
In simple words: This is like transferring a property through direct contact. By "stroking" or rubbing the magnet on the steel, the magnetic property is passed onto the steel bar.

📝 Teacher's Note: This is also known as the "Single Touch Method." Explain that by rubbing, we are essentially aligning the tiny molecular magnets inside the steel in one direction.

🎯 Exam Tip: While "induction" happens without touching, "conduction" or "contact" involves physical touch. Rubbing is a form of magnetization by contact.

Question. The magnetic strength of a bar magnet is :
(a) maximum at its centre
(b) same along the magnet
(c) maximum near its ends
(d) none of these
Answer: (c) maximum near its ends
In simple words: If you try to pick up paperclips with a magnet, they will mostly stick to the tips. This is because the magnetic "pull" is strongest at the North and South poles.

📝 Teacher's Note: Sprinkle iron filings over a bar magnet. Students will see the filings clustering heavily at the ends and almost none at the center.

🎯 Exam Tip: The ends of the magnet where the force is strongest are called "Poles." The center is the "Neutral Region."

Question. The surest test of magnet is :
(a) repulsion
(b) attraction
(c) induction
(d) none of these
Answer: (a) repulsion
In simple words: A magnet can attract both another magnet and a plain piece of iron. However, only a magnet can push away (repel) another magnet.

📝 Teacher's Note: This is a classic trick question. Emphasize that attraction can happen between a magnet and a magnetic substance, but repulsion only happens between two magnets.

🎯 Exam Tip: Always remember: "Repulsion is the only sure test of magnetism."

Question. Nickel is a :
(a) ferromagnetic substance
(b) paramagnetic substance
(c) diamagnetic substance
(d) none of these
Answer: (a) ferromagnetic substance
In simple words: Ferromagnetic materials are "super-attracted" to magnets. Nickel, like iron and cobalt, is a member of this strong magnetic family.

📝 Teacher's Note: Teach the "NIC" acronym: Nickel, Iron, Cobalt. these three are the primary ferromagnetic materials students need to know.

🎯 Exam Tip: Ferromagnetic materials can be turned into permanent magnets, unlike other types of materials.

Question. The substance which form a strong temporary magnet is:
(a) steel
(b) platinum
(c) soft iron
(d) manganese
Answer: (c) soft iron
In simple words: Soft iron is like a "switch." It becomes a magnet instantly when you wrap it in a wire with current, but it loses that power as soon as the electricity is turned off.

📝 Teacher's Note: This is the principle behind electromagnets. Steel would hold onto the magnetism, which we don't want in things like crane lifters or electric bells.

🎯 Exam Tip: Use "soft iron" for temporary magnets (electromagnets) and "steel" for permanent magnets.

Question. The place around a magnet where its influence can be detected is called :
(a) magnetic lines of force
(b) magnetic pole
(c) magnetic field
(d) magnetic space
Answer: (c) magnetic field
In simple words: Just like a heater warms up the air around it, a magnet creates an "invisible bubble" of force around it where it can pull or push other things.

📝 Teacher's Note: Use the analogy of a "Wi-Fi signal area"—you can only connect if you are within the range of the router. A magnetic field is the "range" of the magnet.

🎯 Exam Tip: The magnetic field is a vector quantity, meaning it has both strength and a specific direction.

(B) Subjective Questions

Question. What do you meant by the term pole of a magnet? Magnetically speaking, what is the difference between a piece of brass, a piece of soft iron and a piece of lode- stone?
Answer: Pole of a magnet: Each end of a bar magnet is called its pole. The point situated slightly inside a bar magnet, where most of its magnetic power is concentrated, is called magnetic pole or pole of a magnet.
Brass is not a magnetic substance and it is not affected by magnetic field. It does not stick to a magnet.
Soft iron is a ferromagnetic substance and gets strongly attracted towards a magnet. Soft iron can not attract other magnetic substances unless gets magnetised.
Lode stone is naturally magnetized piece of mineral magnetite. It can attract other magnetic substance.
In simple words: Poles are the "strong spots" at the ends of a magnet. Brass is like wood—magnets ignore it. Soft iron is like a "magnet-fan"—it loves to be near them. Lodestone is a "natural magnet" found in the ground.

📝 Teacher's Note: Point out that magnetic poles actually reside slightly inside the physical ends of the bar, usually at about \( 1/12\text{th} \) of the total length from each end.

🎯 Exam Tip: When distinguishing materials, categorize them: Brass (Non-magnetic), Soft Iron (Magnetic/Ferromagnetic), Lodestone (Natural Magnet).

Question. (a) What are magnetic and non-magnetic substances? Give at least two examples of each.
(b) Fill the blank spaces in the table given below :
Answer: (a) Magnetic substance : Those substances which are affected by the magnetic field are known as magnetic substances. For example : Iron, nickel, cobalt etc. are the magnetic substances.
Non-magnetic substances : Those substance which are not affected by the magnetic field are known as nonmagnetic substances. For example : Paper, glass, wood etc.
(b)

In simple words: Magnetic things (like a nail) get pulled by magnets. Non-magnetic things (like a pencil) are ignored. The table shows that "Likes repel, Unlikes attract."

📝 Teacher's Note: This table is a great way to verify the "repulsion is the sure test" rule. Notice that only magnets cause "repulsion."

🎯 Exam Tip: If a bar attracts both the North and South poles of a needle, it is a magnetic substance (like iron) but not a magnet itself.

Question. Define : magnetic field, magnetic meridian, geographical meridian, declination and magnetic equator.
Answer: Magnetic field : The space surrounding a magnet within which the magnet has its influence is called magnetic field.
Magnetic meridian: The vertical plane containing the magnetic axis of a free suspended magnet at rest, under the action of magnetic intensity of earth is called magnetic meridian.
Geographical meridian : The vertical plane which contains geographical north and south poles of earth at a given place is called geographical meridian.
Declination : The phenomenon due to which the earth’s geographical meridian is inclined to earth’s magnetic meridian is called declination.
Magnetic equator : An imaginary line right bisecting the effective length of bar magnet is called magnetic equator.
In simple words: The field is the magnet's zone. Meridians are like vertical "slices" of the Earth through the poles. Declination is the "error" or angle between a real map and a compass reading.

📝 Teacher's Note: Use a globe and a compass to show that the magnetic North Pole isn't exactly at the "Top" of the Earth's axis. This angle between them is Declination.

🎯 Exam Tip: Definitions of magnetic vs. geographic meridian are frequently asked. Remember that "Meridian" always refers to a "Vertical Plane."

Question. Why do lines of magnetic force never cross? Why do they never pass through a neutral point?
Answer: No two lines of magnetic force cross each other because in that case there would be two directions of resultant magnetic force at a given point, which is not possible.
Magnetic lines of force never pass through neutral point because at neutral point magnetic field due to bar magnet is neutralised by earth’s magnetic field.
In simple words: If the lines crossed, a compass would get confused and try to point in two directions at once, which can't happen! A neutral point is a "dead zone" where the magnet's pull is cancelled out by the Earth's pull.

📝 Teacher's Note: Explain that the tangent to a magnetic field line gives the direction of the field. At a crossing point, you'd have two tangents, which is mathematically impossible for a single point in space.

🎯 Exam Tip: The answer to "why lines don't cross" is a standard two-mark question. Focus on the "resultant direction" argument.

Question. Define : Isogonic line, agonic line isoclinic line.
Answer: Isogonic lines : A line which joins all the places on earth, having same angle of declination is called isogonic line.
Agonic line: A line which joins all the places on earth, having zero angle of declination is called agonic line.
Isoclinic line : A line joining all the places on globe, having same angle of dip or inclination is called isoclinic line.
In simple words: These are map lines. "Iso" means same. "Gonic" is for the angle on the ground (declination). "Clinic" is for the dip angle.

📝 Teacher's Note: Use the root words: Iso (Same) + Gonic (Angle of declination). Agonic literally means "No angle."

🎯 Exam Tip: Don't confuse Isogonic (Declination) with Isoclinic (Dip/Inclination).

Question. How do you account for the following facts?
(a) Iron becomes magnetised when placed in a coil carrying direct current.
(b) Bar magnets lose their magnetism when heated strongly.
(c) Steel makes better permanent magnet than soft iron.
(d) Soft iron keepers help to prevent the magnets from losing their magnetic properties.
Answer: (a) Iron is a magnetic substance and hence its each atom behaves as a tiny magnet. When iron piece is placed in a coil carrying direct current, then all the north poles of all the atoms of iron will align themselves in one direction and all the south poles of all the atoms of iron align themselves in a direction opposite to that to which their north poles point. As a result, iron piece gets magnetised.
(b) Bar magnets lose their magnetism when heated strongly. Due to heat energy, the kinetic energy of the molecules of a bar magnet increases. Thus from straight line molecular chains, they form closed molecular chains and hence, magnetism is lost.
(c) Steel makes better permanent magnet than soft iron because on magnetising steel, steel retain their magnetic behaviour for longer time even after the removal of source which is magnetising the steel. While the soft iron retains the properties of magnetism only so long as the current is passing through the coil.
(d) In magnets, external fields like earth’s magnetic field can randomize the domains. Stray fields from nearby circuits can also disturb the alignment. A keeper for magnets is just a strong permanent magnet that keeps all the domains pointing the same way and realign those that may have gone stray.
In simple words: Current forces the tiny "atom-magnets" to line up. Heat makes them shake so hard they fall out of line. Steel is "sticky" for magnetism, but soft iron is "slippery." Keepers act like a "lock" to keep the magnet's power from leaking.

📝 Teacher's Note: Use the "dancing crowd" analogy: if everyone faces the stage, you have a magnet. If they start dancing (heat), they face random directions and the magnetism is gone.

🎯 Exam Tip: The term "retentivity" is great to use when explaining why steel is better for permanent magnets.

Question. State briefly (a) the molecular theory of magnetism, (b) the modern views on magnetism.
Answer: (a) Ewing suggested the molecular theory of magnetism as follows:
1. Each molecule of a magnetic substance, whether it is magnetised or unmagnetised, is an independent magnet.
2. In a magnetised substance, the molecules are arranged in an order so as to produce an external effect. In this order, all the north poles point to one direction and south poles to the opposite direction.
3. In an unmagnetised substance, the molecules are not arranged in any order, so they neutralise the magnetic forces of each other.
(b) The molecular theory was a big step, but later came an electrical explanation. Atoms consist of negatively charged electrons which revolve around the nucleus. Electrical current loops are formed due to the circulation of these electrons. Each current loop behaves as a magnetic dipole. Also, electrons spin like tops, which adds further magnetism to the atom.
In simple words: Ewing thought everything was made of tiny bar magnets. Modern science says it's actually caused by spinning electrons acting like tiny electric circuits.

📝 Teacher's Note: Clarify that "closed molecular chains" in unmagnetized iron means the magnetic effect of one molecule is cancelled by its neighbor.

🎯 Exam Tip: If asked for modern views, use the keyword "Spin of electrons" and "Orbital motion of electrons."

Question. Describe various methods of magnetising a piece of iron.
Answer: METHODS OF MAGNETISATION :
1. Single Touch Method : The specimen is placed flat. A permanent bar magnet's one pole is placed on one end and drawn to the other end while inclined. It is lifted and repeated. The starting end gets the same polarity as the magnet pole touching it.
2. Divided Touch Method: Opposite poles of two strong bar magnets are placed together in the middle and drawn towards opposite ends. This is repeated several times.
3. Double Touch Method : Similar to divided touch, but a piece of wood or cork is placed between the two magnets to keep them apart as they are moved together from middle to ends.
4. Electrical Method : The specimen is placed inside a long coil (solenoid) and direct current is passed. This makes a very strong magnet. Soft iron becomes a temporary electromagnet, while steel becomes a permanent magnet.
In simple words: You can rub a magnet on iron, use two magnets at once, or use electricity to force the atoms to line up.

📝 Teacher's Note: The electrical method is the most efficient and is how industrial magnets are made. The direction of polarity depends on the direction of current flow (Clockwise = South, Anticlockwise = North).

🎯 Exam Tip: In the single touch method, remember that the end where the magnet is *lifted* acquires the *opposite* polarity to the stroking pole.

Question. What is magnetic induction? Explain it giving a suitable experiment.
Answer: Magnetic induction : The Phenomenon due to which a piece of steel or iron behaves like a magnet when placed near a strong magnet is called magnetic induction.
Experiment : Take a freely suspended magnetic needle. Bring the south pole of a bar magnet near it; the needle is repelled. Now, place a flat piece of iron (AB) between them. The needle is still repelled. Remove the iron—it stays the same. But remove the magnet, and the needle returns to its original position. This proves the iron only acted as a magnet while the real magnet was near it.
In simple words: If you hold a magnet near a nail, the nail becomes a magnet too for a little while. As soon as you take the big magnet away, the nail goes back to being just a normal nail.

📝 Teacher's Note: Induction *precedes* attraction. A magnet first turns the nearby iron into a magnet (induction) and then the opposite poles attract.

🎯 Exam Tip: "Temporary magnetism" is the result of induction in soft iron.

Question. Repulsion is a surer test of magnetic condition of a body than attraction. Explain.
Answer: Repulsion is the surest test of magnetism because the attraction can be caused between two unlike poles of the two magnets OR between a magnet and a plain magnetic substance like iron. But repulsion is ONLY caused when two similar poles of two actual magnets approach each other.
In simple words: A magnet will pull on a piece of steel AND the other end of another magnet. But it will only ever push away another magnet. If it pushes, you know for sure it's a magnet!

📝 Teacher's Note: Use this to explain how a magnetic compass works. It doesn't just attract; it aligns because of the repulsion of like poles.

🎯 Exam Tip: Use this reasoning to explain why we use repulsion to identify the polarity of an unknown magnet.

Question. There are two knitting needles. One of them is magnetised. How will you find out which one is magnetised, if no other magnet is available?
Answer: When an iron bar is magnetised, it slightly increases in length due to setting of molecular magnets along straight chains. So, on precisely measuring the length of knitting needle, the knitting needle which is slightly longer in length than other is magnetised.
In simple words: Magnetizing a needle makes its tiny particles line up in straight rows. This "straightening out" makes the needle a tiny bit longer than a normal one.

📝 Teacher's Note: This is a very subtle physical change called "Magnetostriction." In a school lab, you could also test this by seeing which needle's *middle* can attract the other (a magnet's middle is neutral, but a plain iron bar's middle will be attracted by a magnet's pole).

🎯 Exam Tip: Another way to answer is to bring the end of needle A to the middle of needle B. If there is attraction, A is the magnet. If not, B is the magnet.

Question. Describe two methods of determining the arrangement of the lines of force in the field close to a bar magnet. Give a brief explanation of each method.
Answer: First method : Place a card board on top of a bar magnet and scatter iron filings uniformly. Tap it gently. The filings get magnetised by induction and arrange themselves in curved lines. These lines show the magnetic field.
Second method : Use a small compass needle. Place the magnet on paper and mark a dot at one end of the needle. Move the needle so the other end sits on the dot, and mark a new dot. Repeat this to get a series of dots that form a closed curve from North to South.
In simple words: You can either use "iron dust" to see the whole pattern at once, or use a "tiny compass" to trace the lines one by one like following a trail.

📝 Teacher's Note: Tapping the cardboard is essential to overcome friction so the filings can align freely with the magnetic force.

🎯 Exam Tip: Lines of force always travel from North to South outside the magnet and South to North inside.

Question. Draw diagrams showing the arrangements of the lines of force for:
(a) a single magnet.
(b) two magnets in line, with unlike poles facing one another.
(c) a piece of soft iron laid in line with magnetic field.
Answer: (a) Single magnet: Lines loop from N to S.
(b) Unlike poles: Lines go straight from the N of one magnet to the S of the other, pulling them together.
(c) Soft iron: The lines "bend" and crowd into the soft iron because it is easier for them to travel through iron than air.
In simple words: Magnetic lines are like rubber bands—they try to take the shortest path and they love to dive into iron!

📝 Teacher's Note: This "crowding" of lines into the iron is called "Magnetic Permeability." Iron "conducts" magnetic flux much better than air.

🎯 Exam Tip: In your diagrams, never let the lines of force cross each other.

Question. Give short account of the earth’s magnetic field.
Answer: When a bar magnet is suspended freely, it aligns itself along geographical north-south direction. William Gilbert suggested that earth itself behaves as a huge magnet. It is assumed that:
1. A huge magnet is buried at the centre of earth.
2. The south end of earth’s magnet is towards the earth’s geographic north and vice-versa.
3. The axis of earth’s magnet is not in line with the geographical axis, but makes a small angle with it.
In simple words: The Earth is like a giant ball with a big bar magnet stuck inside it. But the "North" on our maps is actually near the "South pole" of this giant internal magnet!

📝 Teacher's Note: This is why the North pole of our compass points North—it is being attracted by the magnetic South pole located near the geographic North.

🎯 Exam Tip: The angle between the magnetic axis and the geographic axis is approximately \( 17^\circ \).

Question. Give the various methods for demagnetising a magnet.
Answer: 1. Electrical Method : A magnet is placed inside a coil (East-West direction) connected to AC mains. The current is switched on for a minute and the magnet is slowly withdrawn. This randomizes the molecules.
2. By Rough Handling : Dropping the magnet repeatedly or hitting it with a hammer.
3. By Heating : Heating it to a red-hot temperature and letting it cool.
4. By Induction : Placing it near another magnet of same strength with similar poles facing each other for a long time.
5. By Self-Induction : Leaving a magnet alone without keepers; the poles eventually push their own domains out of alignment.
In simple words: To "break" a magnet, you can either cook it, bash it, use confusing electricity, or just let it sit alone until its power leaks away.

📝 Teacher's Note: Explain that AC current is best for demagnetization because it changes direction 50-60 times a second, which totally confuses the alignment of the molecular magnets.

🎯 Exam Tip: Heating and Hammering are the two most common answers. For the electrical method, specify that **Alternating Current (AC)** must be used, not DC.

Question. Describe two simple experiments to support the statement that magnetism is a property of the molecules of a magnet.
Answer: Experiment-1 : Take a bar magnet and break it. Each small part will still have its own North and South pole. No matter how many times you break it, you can never get a single "North-only" piece. This shows magnetism exists in the tiny building blocks.
Experiment-2 : A soft iron bar gets slightly longer when magnetised. This is because the tiny "molecular magnets" are turning to face the same way, stretching the bar out slightly.
In simple words: Breaking a magnet just makes more, smaller magnets. Also, magnets stretch a tiny bit when they "turn on," proving their insides are moving.

📝 Teacher's Note: If magnetism were just a surface property, breaking it would eventually give you non-magnetic pieces. The fact that it doesn't is the strongest proof of the molecular theory.

🎯 Exam Tip: Use the term "dipoles" to describe these tiny molecular magnets.

Question. Explain, why steel is used in preference to soft iron for making permanent magnets while soft iron is used in preference to steel for making electromagnets.
Answer: Steel is used for permanent magnets because it has high "retentivity"—it keeps its magnetism for a very long time once magnetised. Soft iron is used for electromagnets because it has low retentivity; it loses its magnetism instantly when the current stops, making it easy to turn the magnet "on" and "off."
In simple words: Steel is "stubborn" and stays a magnet. Soft iron is "obedient" and only stays a magnet as long as you tell it to with electricity.

📝 Teacher's Note: Retentivity is the ability to retain magnetism. Coercivity is the resistance to being demagnetized. Steel has high values for both.

🎯 Exam Tip: This is a very common "Give Reason" question. Use the words "High Retention" and "Low Retention."

Question. Describe, how you will proceed to determine the position of the pole of a bar magnet.
Answer: Place a bar magnet on paper and draw its outline. Use a small compass needle near one end. Mark two dots (A and B) at the ends of the needle. Move the compass and mark new dots. Join these dots with straight lines. Repeat for several positions. All the lines will point to one spot inside the magnet. That spot is the magnetic pole.
In simple words: Use a compass to see where the "invisible arrows" are pointing. If you draw those arrows as lines, they all meet at the magnet's "heart"—the pole.

📝 Teacher's Note: Remind students that the "Effective Length" (distance between poles) is always less than the "Geometric Length" of the actual metal bar.

🎯 Exam Tip: The effective length is approximately \( 0.84 \) times the actual length of the bar.

Question. Draw lines of force surrounding a bar magnet when it is placed in the magnetic meridian with its (a) north pole pointing geographic, north (b) north pole pointing geographic south.
Answer: (a) N-pole pointing Geo-North: The lines of the magnet and Earth point in opposite directions at the sides, creating two "Neutral Points" on the equatorial line.
(b) N-pole pointing Geo-South: The lines point in opposite directions at the ends, creating two "Neutral Points" on the axial line.
In simple words: When the Earth's pull and the magnet's pull fight each other, they create "Neutral Points" where there is no magnetic pull at all.

📝 Teacher's Note: A neutral point is where the horizontal component of Earth's magnetic field is exactly equal and opposite to the magnet's field.

🎯 Exam Tip: Always mark the 'X' or dots for the Neutral Points in these diagrams; they are the most important part of the grade.

Question. 1. Name the metal used for E and F.
2. Why are E and F placed in contact with the poles of the magnets as shown in the diagram?
3. Mark on the diagram the poles of the second magnet,
4. What is the material of darkened part?
Answer: 1. Soft iron is used for E and F.
2. E and F are placed in contact to form a continuous loop for magnetic lines, which preserves the strength of the magnets.
3. The second magnet must have opposite poles facing the first (N facing S, S facing N).
4. The darkened part is a non-magnetic material like wood or cardboard.
In simple words: Keepers are like "bridges" that let the magnetism circulate in a circle so it doesn't get lost. We use wood between the magnets to stop them from just sticking together.

📝 Teacher's Note: This is a "Magnetic Circuit." By providing a high-permeability path (iron), the lines of force stay contained and don't interact with outside stray fields.

🎯 Exam Tip: Keepers must always be "Soft Iron," never steel, for this purpose.

Question. The figure shows a freely suspended magnet in rest position. Copy the diagram and on it show : (a) Angle of declination (b) Angle in dip
Answer:
In simple words: Declination is the "sideways" angle of the compass. Dip is the "downward" angle where the magnet tries to point into the ground.

📝 Teacher's Note: At the magnetic poles, a magnet would try to point straight down (Dip = \( 90^\circ \)). At the equator, it stays flat (Dip = \( 0^\circ \)).

Question. (a) Since every iron atom is a tiny magnet, why are not all iron bar magnets?
(b) If a magnet is carefully broken into two pieces as shown in figure (i), how does the magnetic strength of each piece compare with that of original magnet? If another magnet is carefully broken in half along its long axis shown in figure (ii), how would the strength of each piece compare with that of original magnet?
Answer: (a) In an unmagnetised iron piece, the tiny atomic magnets are arranged in random directions or closed loops, so they cancel each other out. Only when they are all aligned in one direction does the iron act as a magnet.
(b) 1. Broken across the middle (i) : Each piece becomes a new magnet with the **same pole strength** as the original, but the length is halved.
2. Broken along the axis (ii) : Each piece becomes a new magnet with **half the pole strength** of the original.
In simple words: In a regular nail, the "atom-magnets" are all messy and arguing, so they don't do anything. If you snap a magnet like a twig, the ends are just as strong. but if you slice it like a hotdog, the new thin magnets are only half as strong.

📝 Teacher's Note: Use the "hotdog vs. twig" analogy. Snapping a magnet ( twig style) increases the number of magnets without weakening the "gripping power" of the tips. Slicing it (hotdog style) actually reduces the amount of magnetic material at the tip, weakening it.

🎯 Exam Tip: Snapping perpendicular to length = Same pole strength. Slicing parallel to length = Half pole strength.

Question . Draw the magnetic flux pattern near a bar magnet placed with its axis in the magnetic meridian and the south pole pointing towards geographic north.
Answer:
In simple words: When the South pole faces North, the magnet's field and Earth's field fight each other at the ends. This creates two "dead zones" called neutral points on the line passing through the magnet.

📝 Teacher's Note: When the South pole points North, the neutral points are located on the axial line. When the North pole points North, they are on the equatorial line.

🎯 Exam Tip: Always mark the Neutral Points with an 'X' and ensure your arrows on field lines go from North to South.

Question . Draw a clearly labelled diagram, to show how a steel bar is magnetised by a divided touch method. A written description is not required.
Answer:
In simple words: Two magnets start in the middle of the steel bar and are rubbed outward to the ends at the same time. This "combies" the tiny particles inside the steel to face the same way.

📝 Teacher's Note: Emphasize that the magnets used must be of equal strength and the stroking must be done simultaneously from the center to the opposite ends.

🎯 Exam Tip: Ensure the polarities of the stroking magnets and the resulting poles of the steel bar are correctly shown (opposite to the stroking pole).

Question. Define the terms magnetic declination and dip with reference to freely suspended magnet.
(a) What do you understand by the terms magnetic meridian and geographic meridian?
(b) At what places on the earth will the angle of dip be (1) maximum and (2) minimum?
Answer: Magnetic declination : The angle through which freely suspended magnetic needle is inclined to the geographic axis is known as magnetic declination.
OR
The angle between the geographic meridian and magnetic meridian it is given place is called declination.
Magnetic dip : The angle between the horizontal axis passing through freely suspended magnet and the direction of earth’s magnetic field is called magnetic dip.
(a) Magnetic meridian : The vertical plane containing the magnetic axis of a freely suspended magnet at rest, under the action of magnetic intensity of earth is called magnetic meridian.
Geographic meridian : The vertical plane which contains geographic north and south pole of earth at a given place is called geographic meridian.
(b) The angle of dip is maximum i.e. 90° at the magnetic poles. The angle of dip is minimum i.e. 0° at the magnetic equator.

In simple words: Declination is the angle between "Map North" and "Compass North." Dip is how much a needle tilts down toward the ground. It points straight down at the poles and stays flat at the equator.

📝 Teacher's Note: Use a dip circle or a needle balanced on a horizontal axis to show students how the needle "dips" depending on latitude.

🎯 Exam Tip: Remember the values: Dip = 90° at Poles, Dip = 0° at Equator. This is a very common fill-in-the-blank question.

Question. (a) What are magnetic keepers? What are they used for?
(b) Explain the ‘molecular theory’ of magnetism with the help of a diagram.
Answer: (a) Magnetic keeper : A magnetic keeper is a ferromagnetic bar made from soft iron or steel, which is placed across the poles of a permanent magnet. Magnetic keepers are used to preserve the strength of the magnet by completing the magnetic circuit.
(b) Ewing suggested the molecular theory of magnetism as follows:
1. Each molecule of a magnetic substance, whether it is magnetised or unmagnetised, is an independent magnet.
2. In a magnetised substance, the molecules are arranged in an order so as to produce an external effect. In this order, all the north poles of the molecules of the magnetised substances point to one direction and all their south poles point to a direction opposite to that to which their north poles points.
3. In an unmagnetised substance, the molecules are not arranged in any order, so they neutralise the magnetic forces of each other.
In simple words: Keepers are like "caps" that keep a magnet's power from leaking out. The molecular theory says inside every magnet is a tiny "team" of molecules. If they all face the same way, the magnet is strong. If they are in a messy pile, they cancel each other out.

📝 Teacher's Note: Mention that unmagnetised molecules form "closed chains" where the North of one molecule touches the South of another, creating no external field.

🎯 Exam Tip: For the molecular theory diagram, show the "Magnetised" state with all arrows pointing in one direction (N to S).

Question. What do you understand by the term magnetic declination?
Answer: Magnetic declination : The angle through which freely suspended magnetic needle is inclined to the geographic axis is known as magnetic declination.
OR
The angle between the geographic meridian and magnetic meridian it is given place is called declination.
Magnetic dip : The angle between the horizontal axis passing through freely suspended magnet and the direction of earth’s magnetic field is called magnetic dip.
(a) Magnetic meridian : The vertical plane containing the magnetic axis of a freely suspended magnet at rest, under the action of magnetic intensity of earth is called magnetic meridian.
Geographic meridian: The vertical plane which contains geographic north and south pole of earth at a given place is called geographic meridian.
(b) The angle of dip is maximum i. e. 90° at the magnetic poles. The angle of dip is minimum i.e. 0° at the magnetic equator.

In simple words: It's the difference between where a compass points and where the map says North is. This happens because the Earth's "magnetic spine" is tilted compared to its "spinning axis."

📝 Teacher's Note: This is a repeat of Question 25 from the textbook, stressing how important these definitions are for students.

🎯 Exam Tip: Always distinguish between "Declination" (horizontal angle) and "Dip" (vertical angle).

Question. (a) Explain the mechanism by which unmagnetised iron nails get attracted to a magnet when brought near it.
(b) State any two properties of magnet.
Answer: (a) Every atom of an iron nail behaves as a tiny magnet. Due to the random orientations of these tiny magnets, iron nail does not behave as a magnet. But when iron nail is placed near a magnet, then due to induced magnetism, all the atoms (tiny magnets) align themselves in a particular direction. As a result, the end of the iron nail nearer to magnet acquires the opposite polarity and hence get attracted towards the magnet.
(b) Properties of a magnet :
1. Freely suspended magnet always align itself in the geographic north and geographic south direction.
2. Like poles of magnets repel each other while unlike poles attract.

In simple words: The big magnet acts like a teacher that makes all the messy atoms in the nail "line up" in straight rows. Once they line up, the nail becomes a magnet too, and since its end is the opposite of the big magnet, they stick together!

📝 Teacher's Note: This explains why "Induction precedes attraction." The nail must first become a magnet through induction before it can be pulled by the original magnet.

🎯 Exam Tip: The keyword here is "Induced Magnetism" and "Alignment of atoms."