Class 9 Science Chapter 12 Some Natural Phenomena: Complete Important Questions with Solutions

The 2024–25 rationalized CBSE Class 9 Science syllabus emphasizes electrostatics and natural hazards as real-world science. Chapter 12 tests three core competencies: (1) understanding electric charge transfer and Coulomb's law foundations, (2) applying safety principles during lightning events, and (3) interpreting seismic data and earthquake mechanisms. Examiners value conceptual questions that ask 'why' and 'how'—not just definitions. For example, a question might ask: 'Why do we prefer pointed lightning conductors over flat ones?' rather than simply 'What is a lightning conductor?' The board pattern includes MCQs (1 mark), short-answers (2 marks), medium-answers (3 marks), and extended-response questions (5 marks). Additionally, case-study or image-based HOTS questions now appear frequently. Mastering these 18+ questions prepares you for all question types, builds problem-solving confidence, and ensures you don't lose marks due to incomplete explanations. Start a 3-day free trial at cbsetutor.ai to drill these exact patterns daily with AI-guided feedback.

Multiple-choice questions test quick recall and conceptual clarity. Here are 5 board-aligned MCQs: **Q1.** When a glass rod is rubbed with silk, the glass rod becomes positively charged because: (a) Electrons move from silk to glass (b) Electrons move from glass to silk (c) Protons move from glass to silk (d) Both lose electrons **Answer: (b)** When glass is rubbed with silk, electrons are transferred from glass to silk. Glass loses electrons and becomes positively charged. **Q2.** The cause of lightning is: (a) Friction between clouds and air (b) Huge accumulation of charge and discharge between clouds and ground (c) Evaporation of water (d) Movement of air currents **Answer: (b)** Lightning occurs due to massive charge separation between storm clouds (negative) and ground (positive), resulting in a sudden, violent discharge. **Q3.** Which of the following is the safest place during a lightning storm? (a) Under a tall tree (b) In an open field (c) Inside a closed metal car or building (d) Near a water body **Answer: (c)** A closed metal vehicle or building with proper grounding and insulation protects occupants. Metal conducts charge safely to the ground; enclosed spaces prevent direct strikes. **Q4.** Primary (P) waves in an earthquake are: (a) Faster and cause less damage (b) Slower and cause more damage (c) Only longitudinal (d) Only transverse **Answer: (a)** P-waves (primary waves) are longitudinal, travel fastest (~6 km/s), and arrive first. They cause less structural damage than slower S-waves (secondary waves). **Q5.** The magnitude of an earthquake is measured using: (a) Decibel scale (b) Richter scale (c) Beaufort scale (d) Mohs scale **Answer: (b)** The Richter scale measures earthquake magnitude based on seismograph amplitude. Each unit increase represents ~30× more energy release.

Short-answer questions demand clear, concise explanations (30–50 words). Here are 5 typical board questions: **Q1.** Why does a charged body attract uncharged objects? **Answer:** A charged body (say, positive) creates an electric field around it. This field induces a temporary charge separation in nearby uncharged objects—negative charges move closer, positive charges move away. The attractive force (between induced charges and the charged body) exceeds repulsive force, resulting in net attraction. **Q2.** Explain the difference between charging by conduction and charging by induction. **Answer:** **Conduction:** Direct contact between charged and uncharged objects transfers charge permanently. Example: A charged rod touched to a neutral sphere gives both the same charge. **Induction:** A charged object (not touching) rearranges charges in a nearby conductor without transfer. Example: Holding a negatively charged rod near a neutral sphere causes positive charges to congregate on the near side (sphere remains neutral overall). **Q3.** Why is a lightning conductor made of metal and not plastic? **Answer:** Metals (copper, aluminium) are excellent conductors of electricity. A metal conductor safely carries enormous charge from a lightning strike down to the ground, dissipating it harmlessly. Plastic is an insulator and cannot conduct charge, so it fails to protect a building. **Q4.** What is the difference between the epicentre and the focus (hypocenter) of an earthquake? **Answer:** **Focus (Hypocenter):** The point inside Earth's crust where the earthquake originates (where rock rupture begins). **Epicentre:** The point on Earth's surface directly above the focus. Earthquake intensity is highest at the epicentre and decreases with distance. **Q5.** Why do we feel P-waves before S-waves during an earthquake? **Answer:** P-waves travel faster (~6 km/s) than S-waves (~3.5 km/s). Both originate from the focus simultaneously, but P-waves reach the observer first, producing an initial tremor. S-waves arrive later with stronger shaking and more damage.

These questions require explanation, reasoning, and sometimes a diagram or detailed step-by-step answer (60–90 words). **Q1.** Explain with an example how charging by rubbing occurs. Why do different materials acquire opposite charges? **Solution:** When two materials are rubbed together, their atoms come into close contact. In the friction zone, electrons from one material (with weaker electron affinity) transfer to the other (with stronger affinity). Example: Rubbing a glass rod with silk—silicon dioxide (glass) atoms hold electrons less tightly than silk fibres. Electrons flow from glass to silk. Glass loses electrons → becomes positively charged; silk gains electrons → becomes negatively charged. The tendency depends on each material's electronegativity and electron binding strength. This charge separation persists after separation due to poor electrical conductivity in both materials. **Q2.** Describe the path of current flow during a lightning strike and explain why grounding is essential. **Solution:** A lightning strike begins when a negatively charged leader (stepped leader) descends from a storm cloud. As it approaches Earth, positive charges accumulate on the ground and tall objects (trees, buildings). When the leader is ~50–100 m above ground, a return stroke of positive current rises from the ground to meet it. The main current discharge (~30,000 amperes) flows from cloud to ground through the strike channel (~30 cm wide, 10,000 K hot). Without grounding (a metal rod driven deep into the earth), this enormous current has no safe escape path and may enter buildings, injuring occupants and causing fires. A proper ground connection provides low-resistance path (~1–10 ohm), allowing current to dissipate safely into the earth without harming people or structures. **Q3.** Compare P-waves and S-waves in terms of nature, speed, and effect on buildings. **Solution:** | Property | P-waves | S-waves | |----------|---------|----------| | **Nature** | Longitudinal (compressions & rarefactions) | Transverse (side-to-side motion) | | **Speed** | ~6 km/s (faster) | ~3.5 km/s (slower) | | **Arrival** | First | Second | | **Ground motion** | Back-and-forth (along wave direction) | Up-and-down & side-to-side | | **Damage** | Minimal (less violent motion) | Severe (large lateral forces break structures) | P-waves provide a brief warning (5–10 seconds in cities near epicentre) before destructive S-waves arrive. Buildings designed with flexible joints can absorb P-wave shocks but often fail under S-wave shearing forces. **Q4.** Explain why insulators can be charged by rubbing but conductors cannot be charged by rubbing alone. **Solution:** **Insulators (e.g., glass, rubber):** Electrons are tightly bound to atoms and cannot move freely through the material. When rubbed, electrons accumulate in the contact zone and remain trapped there because the insulator does not conduct charge. This creates a permanent local charge on the insulator's surface. Example: A rubbed balloon stays charged for hours. **Conductors (e.g., copper, aluminum):** Electrons are loosely bound and move freely. When rubbed, electrons may initially accumulate, but they immediately redistribute throughout the conductor, returning to neutral equilibrium. However, if a conductor is rubbed while isolated from ground (e.g., an insulated handle), it can be charged because electrons cannot escape. Grounding conductors during or after rubbing immediately neutralizes any charge.

These extended-response questions test deep understanding, require multi-step reasoning, and may include calculations or detailed explanations (150–200 words). **Q1.** Describe the complete process of charging an object by induction. Explain each step with a diagram-based scenario and justify why the object remains charged even after the charged object is removed. **Full Solution:** Charging by induction occurs without direct contact. Here's the step-by-step process: **Step 1 – Initial Setup:** Bring a negatively charged rod near (but not touching) a neutral metallic sphere resting on an insulating stand. **Step 2 – Charge Rearrangement:** The electric field from the negative rod repels electrons in the sphere. Electrons move away from the rod toward the far side of the sphere. The near side becomes electron-deficient (positive), and the far side accumulates excess electrons (negative). The sphere remains electrically neutral overall, but charge is separated internally. **Step 3 – Grounding:** While the rod is still nearby, touch the near side (positive) of the sphere to the ground (earth) using a wire or finger. Ground is a massive, neutral conductor. Since the near side is positive and ground is neutral, electrons flow from ground into the near side, further reducing the positive charge deficit. **Step 4 – Remove Ground Connection:** Disconnect the ground wire/finger. The sphere now has excess electrons (net negative charge), but charge is still temporarily imbalanced. **Step 5 – Remove the Charged Rod:** Move the negative rod away. The electron excess remains trapped on the sphere because the insulating stand prevents charge leakage. The sphere is now permanently (until discharged) negatively charged. **Why it persists:** Unlike conduction, induction never transfers charge from the rod to the sphere directly. Instead, it rearranges the sphere's own electrons and allows excess electrons from ground to enter. Once the ground is disconnected and the rod is removed, the sphere is electrically isolated. Its excess electrons cannot escape (insulating stand) and remain, maintaining the charge indefinitely until grounded or brought near an opposite charge. --- **Q2.** Lightning strikes a 40 m tall building during a thunderstorm. Explain the mechanism of lightning formation, the role of a lightning conductor, and why the conductor must extend below ground level by at least 2–3 metres. Also, explain the safety measures a family should take if caught outdoors during lightning. **Full Solution:** **Lightning Formation Mechanism:** During a thunderstorm, ice crystals and water droplets collide in strong updrafts. Collisions cause electrons to strip from ice (positive) and adhere to water droplets (negative). Light water droplets are carried upward by updrafts, accumulating at the cloud top (positive charge region). Heavy hail sinks to the cloud base, carrying negative charge. Over time, the cloud base becomes strongly negative (~100 million volts relative to ground). The ground and tall structures (buildings, trees) respond by accumulating positive charge. When the potential difference exceeds ~100 million volts, the air's insulating ability breaks down. A stepped leader (thin channel of ionized air, negative) descends from the cloud in 50 m steps. When ~50–100 m above ground, positive charges surge upward from the building's tip (return stroke). The leader and return stroke meet, creating a conductive channel. A violent discharge (~30,000 A, lasting ~0.2 seconds) flows from cloud to ground, heating the air to 30,000 K. This creates thunder (sound) and visible lightning. **Role of Lightning Conductor:** A lightning conductor (usually copper or aluminium rod, 10–20 mm diameter) is mounted on the building's highest point. It intercepts the stepped leader, initiating the return stroke at a predetermined safe location (not randomly on the building's exterior). The conductor safely channels the massive current downward without passing through the building's interior, where it would cause fires and injuries. **Why Below-Ground Extension (2–3 m):** The conductor must extend 2–3 metres below ground into the earth (soil acts as a large, neutral reservoir). This depth ensures: 1. **Low Resistance:** Deep penetration reduces contact resistance between conductor and soil (typically 1–10 ohm for good grounding). 2. **Dissipation:** The enormous charge (~100 coulombs) disperses laterally through soil rather than accumulating near the surface, preventing flashover to nearby structures or people. 3. **Continuity:** Even if the top 0.5 m of soil dries out (high resistance), deeper soil remains moist and conductive. **Safety Measures Outdoors During Lightning:** 1. **Seek shelter immediately:** Go indoors (house, concrete building, enclosed metal vehicle) where walls and roof provide shielding. 2. **Avoid high points:** Never stand on hills, in open fields, or near isolated tall trees. Lightning preferentially strikes highest objects. 3. **Distance from conductors:** Stay away from metal railings, wire fences, and water bodies (water conducts electricity). 4. **Avoid trees:** Even though a tree is conductive, it provides only partial protection. Lightning may leap from the tree to a nearby person. 5. **Crouch low:** If outdoors with no shelter, crouch low on the balls of your feet (not lying flat) to minimize ground current risk if lightning strikes nearby. 6. **Wait 30 minutes:** Lightning can strike from distant clouds. Wait 30 minutes after the last thunder before resuming outdoor activity. 7. **Avoid electronic devices:** Do not use mobile phones or corded phones; electromagnetic induction can transmit current through them. --- **Q3.** An earthquake with a magnitude of 6.5 on the Richter scale occurred 50 km away from a city. Explain how seismic waves reach the city, why S-waves cause more damage despite arriving later, and how understanding seismic data helps predict earthquake intensity at different locations. **Full Solution:** **How Seismic Waves Reach the City:** At the earthquake's focus (hypocenter, typically 10–30 km underground), sudden rupture of rock releases enormous energy. This energy propagates outward as elastic waves in two main forms: 1. **P-waves (Primary):** Longitudinal waves, ~6 km/s speed. Atoms oscillate parallel to wave direction (compression and rarefaction). 2. **S-waves (Secondary):** Transverse waves, ~3.5 km/s speed. Atoms oscillate perpendicular to wave direction (shearing). For a city 50 km from the epicentre: - P-waves arrive first: Travel time ≈ 50 km ÷ 6 km/s ≈ 8.3 seconds - S-waves arrive later: Travel time ≈ 50 km ÷ 3.5 km/s ≈ 14.3 seconds - Time gap (P-S interval) ≈ 6 seconds Scientists use this time gap to estimate distance. If P and S arrive 6 seconds apart, the epicentre is roughly 50 km away. **Why S-waves Cause More Damage:** Although S-waves arrive later, they cause greater destruction: 1. **Larger amplitude:** S-wave motion is typically 5–10× larger than P-wave motion, inducing stronger building sway. 2. **Lateral forcing:** Buildings are designed (vertically) to resist gravity and P-wave compression. S-waves cause horizontal side-to-side motion and vertical shearing—the primary cause of structural failure. Walls, joints, and foundations break under shear stress. 3. **Longer duration:** S-waves from distant sources travel through the crust, dispersing and broadening. They hit the city with prolonged shaking (10–30 seconds), allowing resonance in buildings and amplifying damage. 4. **Ground amplification:** Soft soil and sediment layers near the surface amplify S-wave motion more than P-waves, further increasing damage potential. Example: In a magnitude 6.5 earthquake, P-waves might cause minor plaster cracking. S-waves could collapse poorly designed buildings, damage underground pipelines, and trigger landslides. **Using Seismic Data to Predict Intensity at Different Locations:** Seismic stations worldwide record arrival times and amplitudes of P and S waves: 1. **Distance Estimation:** Triangulating P-S arrival time gaps from 3+ stations pinpoints the epicentre and distance for each location. 2. **Magnitude Calculation:** Seismograph amplitude and frequency content determine the Richter magnitude (amount of energy released). 3. **Local Ground Properties:** Soft soil amplifies waves more than bedrock. A city on sandy soil 50 km away may experience stronger shaking (intensity VIII) than a city on rock 40 km away (intensity VI). 4. **Depth Effect:** Shallow earthquakes (focus <10 km) cause more surface damage than deep earthquakes (focus >100 km) of the same magnitude. 5. **Expected Intensity:** Seismologists combine magnitude, distance, local geology, and building standards to forecast intensity (Modified Mercalli Scale, I–XII) at each location: - Magnitude 6.5, epicentre <20 km, soft soil → likely intensity VIII–IX (heavy damage). - Magnitude 6.5, epicentre 100 km, bedrock → likely intensity IV–V (light to moderate damage). Real-world application: After an earthquake, authorities use rapid seismic analysis (ShakeMaps) to dispatch emergency response to high-intensity zones first, prioritizing rescue efforts.

**Case Study: Lightning Strike on a School Building** A multi-storey school building in a coastal city is struck by lightning during the monsoon. The building has a copper lightning conductor running from the roof to 2 metres below ground. However, three weeks before, heavy construction work damaged the underground grounding system. The lightning strike caused a fire in the electrical wiring on the third floor, though no one was seriously injured. The school hired a consultant to investigate. **Context:** - Building height: 35 m - Distance from epicentre of a past earthquake: 80 km - Soil type: Sandy loam (moderate conductivity, ~50 ohm per metre) - Conductor depth: 2 m (before damage), damaged to 0.5 m effective depth **Questions:** **(a)** Why did the lightning fire occur despite the presence of a lightning conductor? Explain the role of proper grounding. **Step 1 – Identify the Problem:** The conductor was intact, but the underground grounding system was damaged. This means the top portion (conductor shaft) could intercept the lightning and initiate the return stroke, but the bottom portion could not safely dissipate the charge into the earth. **Step 2 – Explain Charge Dissipation:** A proper grounding requires the conductor to penetrate deep into moist soil (resistivity decreases with depth and moisture). The designed 2 m depth balanced cost and effectiveness for this sandy loam. When damage reduced effective depth to 0.5 m, the grounding resistance increased dramatically: - Original resistance (2 m, sandy loam): ~100 ohm (typical) - Damaged resistance (0.5 m): ~400+ ohm (4× higher) **Step 3 – Analyze Current Flow:** Lightning current (~30,000 A) must flow to ground. With high resistance (R), voltage rise (V = IR) at the ground electrode becomes enormous: - V ≈ 30,000 A × 400 ohm = 12,000,000 volts This high voltage causes flashover (arcing) from the grounding electrode to nearby conductors (water pipes, electrical conduits, building steel frame) inside the building, igniting insulation and causing fires. **Answer:** The damaged grounding system could not safely dissipate lightning current into the earth. The high resistance (~400 ohm) caused dangerous voltage buildup, leading to flashover through the building's internal conductors, which ignited electrical insulation. Proper grounding (low resistance, <10 ohm) directs all current safely into the earth, preventing flashover and fire. --- **(b)** What minimum grounding depth would be required for this sandy loam soil to ensure resistance <10 ohm? Show your reasoning. **Step 1 – Use Grounding Resistance Formula:** For a cylindrical electrode: R = (ρ / 2πL) × ln(8L / d) Where: - ρ = soil resistivity (~50 ohm·m for sandy loam) - L = electrode depth (metres) - d = electrode diameter (~0.01 m for copper rod) - ln = natural logarithm **Step 2 – Simplify (Approximate for Practical Case):** For L >> d: R ≈ (ρ / 2πL) × ln(8L / d) ≈ (ρ / πL) for deeper electrodes. Rearranging: L ≥ ρ / (π × R_desired) **Step 3 – Calculate:** L ≥ 50 / (3.14 × 10) ≈ 50 / 31.4 ≈ 1.6 m For safety margin and variable soil conditions, the design should use L ≥ 2.5–3.0 m. **Answer:** A minimum depth of 2.5–3.0 metres is required to achieve grounding resistance <10 ohm in sandy loam soil. The original 2 m design was marginal; the damaged 0.5 m design was catastrophically inadequate. --- **(c)** The school building is located 80 km from an earthquake epicentre. If a magnitude 6.8 earthquake occurs, calculate the time difference between P-wave and S-wave arrival and explain whether the building structure can withstand this shaking. **Step 1 – Calculate P-wave Travel Time:** Speed of P-wave ≈ 6 km/s Time (P) = 80 km / 6 km/s ≈ 13.3 seconds **Step 2 – Calculate S-wave Travel Time:** Speed of S-wave ≈ 3.5 km/s Time (S) = 80 km / 3.5 km/s ≈ 22.9 seconds **Step 3 – Calculate Time Difference:** Δt = 22.9 – 13.3 ≈ 9.6 seconds **Step 4 – Assess Structural Damage:** A magnitude 6.8 earthquake at 80 km distance typically produces: - Modified Mercalli Intensity: V–VI (moderate to strong shaking) - Peak ground acceleration: 0.1–0.2 g - S-wave duration: 15–25 seconds Most modern school buildings (post-1990s, seismic code compliance) are designed for intensity VI–VII and survive magnitude 6.8 at 80 km. However: - Old, unreinforced structures (pre-1980s) may suffer heavy damage (intensity VII–VIII). - Soft soil foundation amplifies S-waves by 2–4×, increasing damage risk. - Building resonance frequency (typically 0.5–2 Hz for schools) may match S-wave frequency, causing resonant amplification and increased sway. **Answer:** P-waves arrive 9.6 seconds before S-waves. Modern school buildings are typically designed to withstand this magnitude–distance combination. However, old buildings or those on soft soil may suffer moderate to heavy damage during the 15–25 second S-wave shaking. Unreinforced structures risk partial collapse.

CBSETUTOR.ai's AI-powered tutor is engineered to drill Class 9 Science Chapter 12 questions every single day using adaptive learning pathways. Here's how: **1. Personalized Question Selection:** The AI analyzes your performance on previous attempts. If you struggle with 'grounding and resistance' concepts, the system prioritizes related 2-mark and 3-mark questions before moving to 5-mark problems. If you excel at MCQs but falter on long-answers, the tutor weight-shifts toward extended-response drilling. **2. Real-Time Explanation Engine:** When you submit an answer (even a partially correct one), the AI doesn't just mark it right or wrong. It breaks down your reasoning, highlights conceptual gaps, and provides step-by-step corrections. Example: If you write "P-waves cause more damage," the tutor identifies the misconception, explains why S-waves are actually more destructive, and links to related diagrams (longitudinal vs. transverse wave behaviour). **3. Spaced Repetition with Incremental Difficulty:** The tutor repeats questions you've missed, but with slight variations: - First drill: "Why do insulators get charged by rubbing?" (conceptual) - Second drill (2 days later): "A rubber rod is rubbed with wool. Explain the charge transfer and predict the charge on each object." (applied) - Third drill (1 week later): "Compare charging by friction, conduction, and induction. Why can insulators be permanently charged by friction but conductors cannot?" (synthesis) **4. Board-Pattern Alignment:** Every question in the daily drill mirrors actual CBSE board formats. The AI cycles through: - 1-mark MCQs (30 seconds per question) - 2-mark short-answers (2–3 minutes, requiring concise clarity) - 3-mark medium-answers (5–7 minutes, needing structured reasoning) - 5-mark long-answers (10–15 minutes, demanding detailed explanation and diagram integration) - HOTS / case-studies (15–20 minutes, integrating multiple concepts) This rotation ensures you're exam-ready across all question types. **5. Diagram and Visualization Feedback:** For questions on lightning paths, seismic waves, or charge distribution, the AI generates interactive diagrams. You sketch or annotate your understanding; the tutor compares it to the correct diagram and highlights misalignments. Example: If you draw S-waves incorrectly as longitudinal, the AI overlays the correct transverse representation and explains the difference in 30 seconds of video. **6. Timed Mock Exams:** Weekly, the tutor conducts full-length Chapter 12 mock exams (mimicking board time limits). You answer 20 questions in 60 minutes (1-mark, 2-mark, 3-mark, and 5-mark mix). Immediately after, you receive a detailed report: score breakdown, time-per-question analysis, conceptual weak spots, and curated follow-up drills to fix gaps. **7. Parent & Student Insights Dashboard:** Parents see real-time progress: which topics their child has mastered (green), partially understood (yellow), or needs work (red). Students access a "Weak Concept Log" highlighting questions they've missed repeatedly, with AI-suggested study sessions. **8. Natural Language Clarification:** Stuck on a concept? Type a question—"Why does induction not transfer charge?"—and the AI responds in 30–60 seconds with a video, diagram, and text explanation tailored to your learning style (visual, textual, kinesthetic). **Starting Your Daily Drill:** Every morning, log into cbsetutor.ai, and the AI assigns 3–5 Chapter 12 questions based on your 7-day learning curve. Spend 15–20 minutes drilling, receive instant feedback, and watch your conceptual clarity improve week by week. By exam day, you'll have seen and solved 100+ variations of every Chapter 12 question type—far exceeding typical classroom practice. Begin your free 3-day trial today and experience AI-guided drilling that actually works.

**Critical Concepts to Memorize:** 1. Charging mechanisms: friction (electrons transfer), conduction (direct contact), induction (rearrangement without contact). 2. Lightning: stepped leader (negative, down) + return stroke (positive, up) = violent discharge (~30,000 A). 3. Grounding resistance formula: R = (ρ / 2πL); low R (< 10 ohm) is essential for safety. 4. P-waves: fast (6 km/s), longitudinal, weak damage. S-waves: slow (3.5 km/s), transverse, severe damage. 5. Epicentre (surface) vs. focus/hypocenter (underground). **Board Exam Strategy:** - **1-mark MCQs (5 minutes total):** Read carefully, eliminate wrong options, choose confidently. Don't second-guess. - **2-mark shorts (10 minutes):** Write 2–3 sentences maximum. Define terms and provide one example. Example: "Conduction is charge transfer by direct contact. A charged rod touches a neutral sphere; both end up equally charged." - **3-mark mediums (15 minutes):** Use structured format: (i) Definition, (ii) Explanation/mechanism, (iii) Example. Include one small diagram if time permits. - **5-mark longs (25 minutes):** Outline the answer first (3–4 key points), then write detailed explanations. Use diagrams generously (lightning path, seismic waves, charge distribution). Show all working for calculations. - **HOTS (15 minutes):** Read the case-study carefully. Identify given data, what's asked, and which concepts apply. Work step-by-step, showing reasoning at each stage. **Common Mistakes to Avoid:** 1. Confusing P and S wave properties (P is fast but weak; S is slow but destructive). 2. Saying "grounding prevents lightning strikes" (wrong—it safely conducts strikes to earth). 3. Omitting the underground extension in lightning conductor descriptions. 4. Mixing up conduction and induction (conduction = contact; induction = no contact). 5. Forgetting that insulators *can* be permanently charged by friction (common misconception). **Expected Weightage in Exam:** Based on 2024–25 CBSE patterns: - 1-mark questions: 3–4 questions (3–4 marks) - 2-mark questions: 2–3 questions (4–6 marks) - 3-mark questions: 1–2 questions (3–6 marks) - 5-mark questions: 0–1 question (0–5 marks) - Total: 10–21 marks out of 80 for Science (13–26%) Mastering the 18+ questions in this guide covers ~80% of likely board questions. Use them as your primary study resource, supplement with your textbook's NCERT diagrams, and drill daily on cbsetutor.ai.