Some Natural Phenomena — Class 8 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 8 Science chapter "Some Natural Phenomena" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 8 Science chapter "Some Natural Phenomena" — 8 important questions with detailed answers for CBSE board ex…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 8 Science — Some Natural Phenomena. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Some Natural Phenomena — All 8 Questions Solved
Q1. Define lightning. Explain how it is formed.
Lightning is a sudden electrical discharge between clouds or between clouds and the ground. Formation: Friction between water droplets and ice particles in cumulonimbus clouds creates electric charge separation. Lower part becomes negatively charged, upper part becomes positively charged. When potential difference becomes very large (~100 million volts), electrical breakdown occurs, creating a lightning bolt.
Q2. What is thunder? Why does it come after lightning?
Thunder is the sound produced by lightning. When lightning strikes, it heats the air to ~30,000 K, causing rapid expansion and creating a shock wave. This shock wave is the sound we hear as thunder. Light travels much faster than sound (~300,000 km/s vs ~340 m/s), so we see lightning before hearing thunder. Distance = (time gap) × 340 m/s.
Q3. How can we calculate the distance of lightning from us using the time interval between lightning and thunder?
Step 1: Note the time gap between seeing lightning and hearing thunder (in seconds)
Step 2: Use Distance = Speed of sound × Time = 340 m/s × t
Example: If time gap is 3 seconds, Distance = 340 × 3 = 1020 m ≈ 1 km. Light travel time is negligible. Divide by 2 if using round-trip time.
Q4. What is an earthquake? What causes it?
An earthquake is the sudden shaking or trembling of the Earth's surface. Causes: (1) Tectonic plate movement—Earth's crust consists of plates that constantly move, (2) Friction between plates builds stress, (3) When stress exceeds the strength of rocks, they suddenly break and slip, (4) This sudden release of energy creates seismic waves that cause shaking and destruction.
Q5. What is the Richter scale? What does it measure?
The Richter scale measures the magnitude (strength) of earthquakes. It ranges from 1 to 9. Magnitude represents the energy released during an earthquake. Scale: 1-3 (not felt), 3-4.5 (slight to moderate damage), 4.5-6 (serious damage), 6-7 (major damage), >7 (devastating). Each unit increase represents ~30 times more energy.
Q6. Name three safety precautions to follow during an earthquake.
(1) Drop, Cover, Hold On: Drop to hands and knees, cover head with arms under a sturdy table or desk. (2) Stay indoors: Avoid going outside where falling debris or power lines are dangerous. (3) Avoid elevators: Use stairs only. (4) Stay away from windows and heavy objects. (5) After the quake, remain alert for aftershocks.
Q7. How are seismic waves detected and recorded?
Seismic waves are detected using instruments called seismographs. A seismograph contains a pendulum or mass suspended by a spring that moves with ground vibrations. The movement is recorded on a rotating drum or electronically. Seismometers measure amplitude and frequency of ground motion. Networks of seismographs worldwide detect earthquakes and determine epicenter location by triangulation.
Q8. What is the difference between epicenter and focus (hypocenter) of an earthquake?
Focus (Hypocenter): The point inside the Earth where the earthquake originates and energy is released. It is the actual location where rock rupture occurs. Epicenter: The point on Earth's surface directly above the focus. It is the location closest to the focus and usually experiences the strongest shaking. Epicenter is determined by seismograph triangulation.
Some Natural Phenomena — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the phenomenon of electric discharge occurring between clouds or between clouds and the Earth called?
- A. Earthquake
- B. Cyclone
- C. Lightning
- D. Tsunami
Answer: C. Lightning — Lightning is the sudden and visible discharge of electricity that occurs between oppositely charged clouds, or between charged clouds and the ground.
MCQ 2. During a thunderstorm, it is safest to take shelter:
- A. Under a tall tree
- B. In an open field
- C. Inside a car with windows closed
- D. Near a water body
Answer: C. Inside a car with windows closed — A car with closed windows acts as a Faraday cage, providing a safe enclosure during lightning because the metallic body conducts the charge to the ground without affecting the occupants inside.
MCQ 3. Which of the following describes the principle behind how a lightning conductor works?
- A. It attracts all the lightning strikes to one point.
- B. It provides a low-resistance path for the electrical discharge to the ground.
- C. It repels the lightning strikes away from the building.
- D. It stores the electrical energy from lightning for later use.
Answer: B. It provides a low-resistance path for the electrical discharge to the ground. — A lightning conductor provides a direct, low-resistance path for the huge electrical energy of lightning to flow safely into the earth, thus protecting the building from damage.
MCQ 4. The instrument used to detect the presence of charge on a body is called a/an:
- A. Barometer
- B. Seismograph
- C. Electroscope
- D. Anemometer
Answer: C. Electroscope — An electroscope is a scientific instrument used to detect the presence and magnitude of electric charge on a body.
MCQ 5. What causes the spectacular flash of light and sound (thunder) during lightning?
- A. Chemical reaction in the air
- B. Rapid heating and expansion of air by the electric discharge
- C. Friction between clouds
- D. Reflection of sunlight
Answer: B. Rapid heating and expansion of air by the electric discharge — The immense heat generated by the electric discharge of lightning rapidly heats the air along its path, causing it to expand explosively, which produces the thunderclap.
MCQ 6. Which type of charge tends to accumulate at the top edges of thunderclouds?
- A. Positive charges
- B. Negative charges
- C. Neutral charges
- D. Both positive and negative equally
Answer: A. Positive charges — During a thunderstorm, due to friction and air currents, positive charges tend to accumulate near the top edges of the clouds, while negative charges gather near the lower edges.
MCQ 7. Why is it recommended to unplug electrical appliances during a thunderstorm?
- A. To save electricity
- B. To prevent damage from power surges caused by lightning
- C. To reduce noise interference
- D. To improve television signal
Answer: B. To prevent damage from power surges caused by lightning — Unplugging electrical appliances during a thunderstorm protects them from damage caused by power surges and spikes that can occur if lightning strikes the power lines or the building.
MCQ 8. The sudden shaking or trembling of the Earth's crust is known as a/an:
- A. Cyclone
- B. Tsunami
- C. Earthquake
- D. Landslide
Answer: C. Earthquake — An earthquake is defined as the sudden shaking or trembling of the Earth's crust, caused by the movement of tectonic plates.
MCQ 9. What is the main cause of earthquakes?
- A. Volcanic eruptions
- B. Movement of Earth's tectonic plates
- C. Strong winds
- D. Heavy rainfall
Answer: B. Movement of Earth's tectonic plates — Earthquakes are primarily caused by the sudden release of energy due to the movement and friction of the Earth's tectonic plates along fault lines.
MCQ 10. The instrument used to detect and record the intensity and duration of an earthquake is called a:
- A. Thermometer
- B. Barometer
- C. Seismograph
- D. Hydrometer
Answer: C. Seismograph — A seismograph is an instrument that detects and records ground motion during an earthquake, producing a seismogram.
MCQ 11. The magnitude of an earthquake is measured on the:
- A. Celsius scale
- B. Richter scale
- C. pH scale
- D. Kelvin scale
Answer: B. Richter scale — The Richter scale is used to quantify the magnitude of an earthquake, which indicates the energy released at the earthquake's source.
MCQ 12. If you are outdoors during an earthquake, what is the safest action to take?
- A. Stand near a tall building
- B. Run into a nearby forest
- C. Move to an open clear space away from buildings and trees
- D. Get into a car and drive away quickly
Answer: C. Move to an open clear space away from buildings and trees — During an earthquake, if outdoors, the safest action is to move to an open area away from buildings, trees, power lines, and other structures that could collapse or fall.
MCQ 13. The point inside the Earth where an earthquake originates is called the:
- A. Epicentre
- B. Focus
- C. Crust
- D. Mantle
Answer: B. Focus — The focus (or hypocenter) is the point within the Earth's crust where the earthquake originates, while the epicentre is the point on the Earth's surface directly above the focus.
MCQ 14. Which of the following statements about the Richter scale is correct?
- A. An increase of one unit on the Richter scale means a 10-fold increase in the amplitude of seismic waves.
- B. It measures the depth of the earthquake's focus.
- C. It is a linear scale.
- D. An earthquake of magnitude 2.0 is highly destructive.
Answer: A. An increase of one unit on the Richter scale means a 10-fold increase in the amplitude of seismic waves. — The Richter scale is logarithmic, meaning that each whole number increase in magnitude represents a ten-fold increase in the measured amplitude of seismic waves.
MCQ 15. Which of these natural phenomena is NOT caused by the movement of Earth's plates?
- A. Earthquakes
- B. Tsunami
- C. Volcanic eruptions
- D. Lightning
Answer: D. Lightning — Earthquakes, tsunamis (often triggered by undersea earthquakes), and volcanic eruptions are all related to the movement and interaction of Earth's tectonic plates. Lightning is an atmospheric electrical discharge.
MCQ 16. When lightning strikes, what is the safest place to be indoors?
- A. Near a window
- B. In the centre of a room
- C. Under a tree indoors (if any)
- D. By the main electrical panel
Answer: B. In the centre of a room — During a thunderstorm, it is safest to stay away from windows, doors, and electrical appliances. The centre of a room in a structurally sound building provides good protection.
MCQ 17. Why do lightning conductors have a sharp, pointed end at the top?
- A. To make them look aesthetically pleasing
- B. To attract more lightning strikes
- C. To facilitate the collection and channeling of electrical charges to the ground
- D. To reflect sunlight
Answer: C. To facilitate the collection and channeling of electrical charges to the ground — The sharp, pointed end of a lightning conductor helps to gather the charge and provide a better pathway for the lightning's immense electrical energy to safely flow to the ground.
MCQ 18. What is a fault line?
- A. A line showing incorrect data on a map
- B. A crack or fracture in the Earth's crust where movement occurs
- C. A boundary between land and ocean
- D. A geological layer rich in fossils
Answer: B. A crack or fracture in the Earth's crust where movement occurs — A fault line is a fracture or zone of fractures between two blocks of rock in the Earth's crust, where movement has occurred, leading to earthquakes.
MCQ 19. Which part of the Earth's structure is primarily involved in the movement that causes earthquakes?
- A. Inner core
- B. Outer core
- C. Mantle
- D. Crust
Answer: D. Crust — Earthquakes mostly originate in the Earth's crust, which is the outermost layer, due to the movement and interaction of the tectonic plates that form it.
MCQ 20. The seismic waves that typically cause the most damage to buildings during an earthquake are the:
- A. P-waves (primary waves)
- B. S-waves (secondary waves)
- C. Surface waves
- D. Body waves
Answer: C. Surface waves — Surface waves travel along the Earth's surface and have a larger amplitude and slower speed compared to P-waves and S-waves, causing the most significant ground shaking and structural damage to buildings.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.