Some Natural Phenomena
Focused last-minute revision notes with clear concepts, exam traps, key comparisons and compact practice.
Chapter Snapshot
- Objects can become electrically charged by rubbing.
- Like charges repel; unlike charges attract.
- An electroscope detects electric charge.
- Lightning is a large electrical discharge in the atmosphere.
- A lightning conductor provides a safer path for charge to reach the ground.
- During thunderstorms, avoid open fields, isolated tall objects, metal fences and wired electrical equipment.
- Earthquakes result from sudden movement within Earth, commonly along faults or plate boundaries.
- The underground origin is the focus; the point above it on the surface is the epicentre.
- Seismic waves are recorded by seismographs.
- Preparedness and safe building design reduce earthquake risk.
What You Will Learn
- Explain charging by rubbing
- State interaction of charges
- Explain electroscope principle
- Describe lightning formation broadly
- Apply lightning safety
- Explain focus, epicentre and seismic waves
- Describe earthquake safety
Last-Minute Chapter Map
Lightning and earthquakes have different causes, so their safety measures are different.
1. Electric Charges
Rubbing certain materials can transfer electrons and leave objects electrically charged. Two charged objects may attract or repel. Like charges repel and unlike charges attract.
2. Electroscope
An electroscope detects the presence of electric charge. In a simple leaf electroscope, charge spreads to two thin leaves; similar charges on the leaves repel, making them diverge.
3. Lightning
Clouds contain moving water droplets and ice particles. Charge separation can build a very large potential difference. When the electric field becomes strong enough, air breaks down and a sudden discharge occurs: lightning.
4. Lightning Safety
The safest place is usually inside a substantial building or a closed vehicle. Avoid open fields, hilltops, isolated trees, metal fences and contact with wired electrical appliances or plumbing during severe storms. If no shelter exists, minimise height and contact area; do not lie flat.
5. Lightning Conductors
A lightning conductor is a metal system installed on buildings to provide a low-resistance path for lightning current to reach the ground, reducing the chance of destructive current passing through the structure.
6. Earthquakes
An earthquake is shaking of the ground caused by sudden energy release within Earth. Many earthquakes occur when rocks slip along faults due to movement of tectonic plates.
7. Focus, Epicentre and Seismic Waves
The point inside Earth where rupture begins is the focus (hypocentre). The point on the surface directly above is the epicentre. Energy travels outward as seismic waves, recorded by instruments called seismographs.
8. Earthquake Safety
During shaking indoors, Drop, Cover and Hold On under sturdy furniture, stay away from glass and do not use lifts. Outdoors, move away from buildings, trees and power lines. Prepared buildings and emergency planning reduce injuries.
Lightning vs Earthquake
| Feature | Lightning | Earthquake |
|---|---|---|
| Cause | Electrical discharge in atmosphere | Sudden energy release in Earth |
| Main hazard | Electric current, fire | Ground shaking, collapse |
| Key protection | Safe shelter / lightning protection | Earthquake-resistant construction and Drop-Cover-Hold |
Exam Focus
Must Revise Before the Exam
- Charging by rubbing
- Like/unlike charges
- Electroscope
- Lightning and conductor
- Thunderstorm safety
- Earthquake cause
- Focus vs epicentre
- Seismic waves
- Earthquake safety
Common Mistakes
Key Terms
Key Terms
Quick Revision
Quick Revision
- Rubbing can transfer charge.
- Like charges repel; unlike charges attract.
- Electroscope detects charge.
- Lightning is a massive electrical discharge.
- Seek substantial shelter during thunderstorms.
- Lightning conductor carries current safely toward ground.
- Earthquake focus is inside Earth; epicentre lies above it at surface.
- Seismographs record seismic waves.
- Drop, Cover and Hold On during strong shaking.
Practice Questions
Like electric charges:
A. attract
B. repel
C. never interact
D. become magnetic
View Solution
Correct Answer: B. repel
Like charges repel.
The point inside Earth where an earthquake begins is the:
A. epicentre
B. focus
C. equator
D. orbit
View Solution
Correct Answer: B. focus
The focus is the underground origin.
The safest place during lightning is generally:
A. under an isolated tree
B. in an open field
C. inside a substantial building
D. on a hilltop
View Solution
Correct Answer: C. inside a substantial building
Substantial enclosed shelter provides much better protection.
An instrument that records seismic waves is a:
A. thermometer
B. seismograph
C. barometer
D. ammeter
View Solution
Correct Answer: B. seismograph
Seismographs record ground motion from seismic waves.
How does a lightning conductor protect a building?
View Solution
It provides a low-resistance metallic path that carries lightning current safely toward the ground instead of through the building structure.
Differentiate focus and epicentre.
View Solution
Focus is the point inside Earth where rupture starts; epicentre is the point on Earth’s surface directly above the focus.
What should you do if strong earthquake shaking begins while you are inside a classroom?
View Solution
Drop to the ground, take cover under sturdy furniture, hold on, stay away from windows and do not rush to stairs or lifts during shaking.
Chapter Summary
Chapter Summary
- Rubbing can transfer charge.
- Like charges repel; unlike charges attract.
- Electroscope detects charge.
- Lightning is a massive electrical discharge.
- Seek substantial shelter during thunderstorms.
- Lightning conductor carries current safely toward ground.
- Earthquake focus is inside Earth; epicentre lies above it at surface.
- Seismographs record seismic waves.
- Drop, Cover and Hold On during strong shaking.