Class 9 Science Chapter 4 Exploring Magnets: 18 Important Questions with Complete Solutions

The 2026-27 CBSE Class 9 Science syllabus emphasizes conceptual understanding over rote memorization. Chapter 4 is typically allotted 8–10 marks in board exams, distributed across multiple question types. The rationalized NCERT curriculum focuses on observable, hands-on knowledge: distinguishing magnetic from non-magnetic materials through attraction tests, identifying magnetic poles and their interaction rules, understanding Earth's magnetism and compass orientation, and the practical method of magnetizing iron. Board examiners test both factual recall (What are magnetic poles?) and application-level thinking (Why does a compass needle align north-south? How would you magnetize a needle using a bar magnet?). Students who master the logical sequence—from material properties → pole interaction → Earth's field → practical magnetization—tend to score higher marks. These 18 questions are deliberately structured to build that progression, ensuring no learning gap remains before your board exam.

Multiple-choice questions test quick recall and concept clarity. They appear in the objective section of board papers and demand accurate understanding in seconds. **Q1. Which of the following is a non-magnetic material?** A) Iron B) Cobalt C) Nickel D) Copper **Answer: D) Copper** Explanation: Copper does not possess magnetic properties and is not attracted to a magnet. Iron, cobalt, and nickel are ferromagnetic materials. **Q2. The region around a magnet where magnetic force can be experienced is called:** A) Magnetic equator B) Magnetic field C) Magnetic pole D) Magnetic axis **Answer: B) Magnetic field** Explanation: A magnetic field is the invisible region of magnetic influence around a magnet where a magnetic force acts on other magnetic materials. **Q3. Two similar magnetic poles:** A) Attract each other B) Repel each other C) Are neutral D) Do not interact **Answer: B) Repel each other** Explanation: Like poles (North-North or South-South) always repel, while opposite poles (North-South) attract. **Q4. The Earth acts as a:** A) Permanent magnet B) Electromagnet C) Temporary magnet D) Non-magnet **Answer: A) Permanent magnet** Explanation: Earth possesses a permanent magnetic field due to molten iron in its outer core, making it function as a giant permanent magnet. **Q5. A compass needle points towards:** A) Geographic North B) Magnetic North C) True North D) Magnetic South **Answer: B) Magnetic North** Explanation: A compass needle aligns with Earth's magnetic field lines and points toward the magnetic North pole, which is close to but not identical to geographic North.

Short-answer questions require concise but complete explanations. They test understanding of definitions, simple relationships, and basic phenomena. **Q1. Distinguish between magnetic and non-magnetic materials with one example each.** Answer: Magnetic materials are those that are attracted to a magnet and can be magnetized (e.g., iron, nickel, cobalt). Non-magnetic materials are not attracted to magnets and cannot be magnetized (e.g., wood, plastic, copper). Iron is magnetic—it is attracted to a magnet. Rubber is non-magnetic—a magnet has no effect on it. **Q2. Why is it not possible to separate the two poles of a magnet by breaking it in half?** Answer: When a magnet is broken, each fragment develops its own North and South poles. The poles are inseparable because they always exist together as a pair in every magnetic material. Breaking a magnet creates two new magnets, each with complete North-South polarity, rather than isolating individual poles. **Q3. What is a compass? How does it help us find direction?** Answer: A compass is a simple instrument consisting of a magnetic needle (usually made of magnetized iron) suspended freely on a pivot. The needle aligns itself with Earth's magnetic field and points toward the magnetic North pole, helping users determine cardinal directions (North, South, East, West) and navigate accurately. **Q4. State the rule for magnetic attraction and repulsion.** Answer: Unlike poles (North and South) of two magnets attract each other. Like poles (North-North or South-South) of two magnets repel each other. This rule holds for all magnetic interactions between poles. **Q5. Describe one method of making a magnet using a bar magnet.** Answer: Stroking method: Take an unmagnetized iron rod or needle. Stroke it repeatedly in one direction using one pole (say North pole) of a bar magnet, lifting the magnet after each stroke. After 40–50 strokes in the same direction, the iron rod becomes magnetized because the atomic magnets align in the same direction. The end where the North pole stroked becomes the South pole of the new magnet.

Three-mark questions test deeper understanding, logical reasoning, and the ability to link concepts. These often appear in the short-answer section of board papers. **Q1. A student observes that a magnet attracts iron filings. Explain why not all materials behave this way. Also, explain what happens at the atomic level in iron during magnetization.** Answer: Not all materials are attracted to magnets because only ferromagnetic materials (iron, cobalt, nickel) possess unpaired electrons that generate atomic magnetic dipoles. In non-magnetic materials like copper or wood, electrons are paired, canceling their magnetic effects. At the atomic level, iron atoms have inherent magnetic moments. When an external magnet is brought near, these atomic magnets experience a torque and align in the direction of the external magnetic field. Once aligned, the combined effect of billions of aligned atomic magnets produces a strong net magnetic force, causing iron filings to be attracted. **Q2. The geographic North pole and magnetic North pole of Earth are not in the same location. Why does a compass still help us navigate? What is declination?** Answer: Although geographic and magnetic North poles differ by approximately 11° in longitude, a compass remains useful because it consistently points toward magnetic North. Navigation systems account for this difference. Declination (or magnetic declination) is the angle between true geographic North and magnetic North at any given location. Modern navigation tools and maps include declination values so users can adjust their heading from the compass reading to true North. For most practical navigation on land, this small difference (typically 5–15°) is acceptable for short-distance travel. **Q3. A teacher magnetized an iron nail by stroking it with a magnet. The next day, the nail had lost some magnetism. Explain why this happens and suggest a method to prevent this loss.** Answer: Magnetism is lost because the atomic magnets in the iron nail gradually become randomly oriented due to thermal motion, mechanical vibration, and time. This process is called demagnetization. The aligned structure of magnetic domains becomes disordered, weakening the net magnetic field. To prevent loss: (1) Store the magnetized nail away from heat and vibration, (2) Keep it away from other magnets or non-aligned magnetic materials that could disturb domain alignment, (3) Store it in a soft iron keeper (a yoke) that provides a closed magnetic circuit, reducing external field perturbation, or (4) Re-magnetize it periodically using the stroking method. **Q4. Explain why Earth's magnetic field is stronger at the magnetic poles than at the magnetic equator.** Answer: Earth's magnetic field originates from convection currents of molten iron in the outer core. These currents generate a dipole magnetic field similar to a bar magnet. At the magnetic poles (near the axis of this dipole), magnetic field lines are most concentrated and densely packed, resulting in maximum field strength. At the magnetic equator, field lines are more spread out and run parallel to Earth's surface, resulting in weaker net vertical component. This is why a compass needle dips more steeply at higher latitudes near the poles and remains nearly horizontal at the equator (magnetic inclination varies with latitude). The field strength ≈ 25–65 microtesla at poles versus ≈ 30 microtesla at equator, with directional variation determining the dip angle.

Five-mark questions demand comprehensive explanations, step-by-step reasoning, and often combine multiple concepts. These carry significant weight in board exams. **Q1. Describe the process of magnetizing an iron rod using a bar magnet. Also explain what happens to the atomic structure of iron during this process and why the rod retains magnetism even after the bar magnet is removed.** Full Solution: (a) **Magnetization Process (Stroking Method):** — Take an unmagnetized soft iron rod and a bar magnet. — Hold the rod horizontally on a non-magnetic stand. — Starting from one end, stroke the rod along its length using the same pole of the bar magnet (e.g., North pole). — Lift the magnet slowly at the end and return it to the starting position without touching the rod. — Repeat this stroking motion 40–50 times in the same direction. — The iron rod becomes magnetized; the end where the North pole stroked becomes the South pole, and the opposite end becomes the North pole. (b) **Atomic-Level Explanation:** — Iron atoms possess electrons with unpaired spins, creating atomic magnetic moments (tiny dipoles). — In an unmagnetized rod, these atomic dipoles are randomly oriented in all directions, their fields canceling out. — When an external magnet is brought near, it applies a torque on the atomic dipoles, forcing them to align parallel to the external magnetic field. — Stroking repeatedly reinforces this alignment, organizing the dipoles into ordered domains. — Once aligned, billions of atomic magnetic moments add vectorially, creating a macroscopic magnetic field. (c) **Why Magnetism is Retained:** — Soft iron has a low coercivity (resistance to demagnetization). — The aligned domains in soft iron remain in their ordered state due to exchange interaction (quantum mechanical coupling between neighboring atomic spins). — Once established, the domain alignment is energetically stable and persists even without the external magnet. — Over time, thermal motion and mechanical vibration gradually randomize domains, causing slow demagnetization (usually weeks to months). **Q2. A student uses a compass to navigate. Explain Earth's magnetic field, magnetic inclination, and magnetic declination. Why are these concepts important for accurate navigation?** Full Solution: (a) **Earth's Magnetic Field:** — Earth behaves as a giant permanent magnet due to convection currents of molten iron in the outer core (Gutenberg layer). — These moving charges (ions and electrons) generate a magnetic field with a North pole near the geographic South pole and a South pole near geographic North (by convention, we call the pole toward geographic North the "magnetic North"). — The magnetic field extends thousands of kilometers into space (magnetosphere) and protects Earth from solar wind. — Field strength: approximately 25–65 microtesla, varying with latitude. (b) **Magnetic Inclination (Dip Angle):** — Magnetic field lines emerge from the magnetic South pole and curve around Earth to enter the magnetic North pole. — At the magnetic poles, these lines are nearly vertical (perpendicular to Earth's surface). — At the magnetic equator, lines are nearly horizontal (parallel to surface). — Inclination is the angle below the horizontal at which a freely suspended magnetic needle aligns. — At magnetic poles: inclination ≈ 90° (needle points straight down/up). — At magnetic equator: inclination ≈ 0° (needle is horizontal). — In India (latitude ~25°N): inclination ≈ 30–35° (needle tilts downward). (c) **Magnetic Declination:** — Declination is the angle between true geographic North and magnetic North. — Magnetic North does not align exactly with geographic North; it varies by ~11° longitude globally. — In India: declination is approximately 1–2°W (magnetic North is 1–2° west of true North). — Declination changes with geographic location and slowly over time (decades) due to core convection variations. (d) **Importance for Accurate Navigation:** — A compass points toward magnetic North, not true geographic North. — Without accounting for declination, navigation errors accumulate: e.g., 5° error over 100 km ≈ 8.7 km lateral drift. — Modern maps and GPS systems provide declination values so users can adjust compass readings to true North. — Mariners and pilots use nautical charts with declination isogons marked to maintain accurate courses. — Understanding inclination prevents false readings in inclinometers used for surveying and geology. **Q3. A bar magnet is broken into three pieces: two small magnets from the ends and one rectangular piece from the center. Predict the polarity of each piece and explain why you cannot obtain a monopole (single isolated pole).** Full Solution: (a) **Polarity of Broken Pieces:** — Original bar magnet: North pole at one end, South pole at the other. — End pieces (small magnets): · The small magnet from the North end becomes a new magnet with North pole on the exposed face and South pole on the internal face (facing the center piece). · The small magnet from the South end becomes a new magnet with South pole on the exposed face and North pole on the internal face. — Center piece: · The rectangular center portion becomes a magnet with North pole on one face (internal) and South pole on the other (internal face). · Both exposed faces were originally internal surfaces; the center piece retains complete North-South polarity. (b) **Why Monopoles Cannot Exist:** — Every piece, no matter how small, develops complete North and South poles. — At the atomic level, each electron spin (source of magnetic moment) is a dipole: it generates a magnetic field with both North and South components. — Magnetic dipoles cannot be separated into isolated poles; they always pair. — If we theoretically cut down to a single atom or electron, the magnetic moment itself is a dipole. — This is fundamentally different from electric charge, where positive and negative charges can be isolated. — Mathematically, magnetic monopoles would satisfy ∇·**B** ≠ 0, but experimentally ∇·**B** = 0 always (no magnetic monopoles detected in 150+ years of physics). — Therefore, isolated North or South poles (monopoles) do not and cannot exist in nature.

**Case-Study Question: Magnetized Compass in an Unusual Location** **Scenario:** A geologist travels to a cave in the Himalayas and finds that her compass needle does not point toward true North. Instead, it consistently points 35° to the west. She also notices that when she places the compass on the ground (horizontal orientation), the needle tilts downward at an unusual 60° angle. The local rocks contain high concentrations of magnetite (Fe₃O₄), a strong natural magnet. **(a) What is happening here? Identify the two anomalies and explain their causes.** **(b) Which compass readings—magnetic inclination or magnetic declination—are affected by the magnetite rocks? Explain why.** **(c) How would the geologist correct her compass readings to determine true geographic direction?** **(d) If the geologist broke a magnetite stone in half, would each half still exhibit magnetism? Justify your answer using pole theory.** **Full Solution:** **(a) Two Anomalies and Their Causes:** Anomaly 1: Compass needle points 35° west of true North instead of aligning with magnetic North. — This is an extreme magnetic declination caused by local magnetic interference from magnetite rocks. — Magnetite is a strong ferromagnetic mineral (Fe₃O₄) with permanent magnetic properties. — The concentrated magnetite deposits in the cave create a powerful localized magnetic field that dominates over Earth's weaker background magnetic field. — The compass needle aligns with this stronger local field rather than Earth's magnetic North. — Normal declination in the Himalayas ≈ 1–2°W; 35°W is clearly anomalous. Anomaly 2: The compass needle tilts downward at 60° instead of Earth's normal inclination (≈ 35°–45° in the Himalayas). — This reflects an abnormal magnetic inclination caused by the magnetite field's geometry. — If the magnetite deposit has a North pole oriented downward into the ground, its field lines would point steeply downward, forcing the compass needle to dip to 60°. — This extreme inclination is produced by the vectorial addition of the local magnetite field and Earth's field. **(b) Affected Reading: Magnetic Declination (Primarily) and Inclination (Secondarily)** Magnetite rocks affect both, but primarily declination: — **Magnetic Declination** is the horizontal angular deviation of the compass needle from true North. The 35°W deviation is directly caused by the local magnetite field's horizontal component dominating the compass. — **Magnetic Inclination** is the angle of dip below horizontal. The anomalous 60° tilt reflects the vertical component of the local field. Magnetite with a downward-pointing pole creates a steep downward field that the compass needle follows. Why magnetite causes these effects: — Magnetite produces a dipole field (like any magnet) with regional influence, overriding the global Earth magnetic field locally. — The compass needle is sensitive to the vector sum of all magnetic fields; if the local magnetite field is stronger, the needle responds to it exclusively. — The effect is strongest close to the ore deposit and decreases with distance (field strength ∝ 1/r³). **(c) Correcting the Compass Reading:** Step 1: Measure the magnetic declination locally using astronomical observation or GPS. — Observe the true North direction using star positions or a GPS receiver. — Compare the compass reading to the true North direction: the difference is local declination = 35°W. Step 2: Adjust the compass bearing. — If the compass points 35° west of true North, add 35° to any compass bearing to obtain true bearing. — Example: Compass reads 90° (east); true bearing = 90° + 35° = 125° (roughly south-southeast). Step 3: Use an alternative navigation method. — If magnetite interference is severe, use GPS, celestial navigation (sun or stars), or topographic landmark navigation. — Mark declination on maps before travel to avoid repeated errors. **(d) Would magnetite break into two magnetic pieces?** **Yes, each half would exhibit magnetism.** Explanation: — Magnetite (Fe₃O₄) is a ferromagnetic material with atomic magnetic moments aligned in a crystal structure. — When broken, the piece separates at the atomic level but does not isolate individual poles. — Each fragment develops a complete North-South pole configuration from the realignment of atomic dipoles at the new surface. — Even the smallest magnetite particle (if not shattered into atomic scale) remains magnetic because atomic dipoles are intrinsic to iron atoms and cannot be separated. — You cannot obtain a monopole—a piece of pure North or pure South pole—no matter how finely you divide magnetite. This principle is universal for all ferromagnetic materials and applies equally to magnetite.

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