Olympiad Test: Some Natural Phenomena - 1 - Class 8 MCQ

When two bodies are rubbed against each other, they acquire equal and opposite charges.
Explanation:
When two bodies are rubbed against each other, a process known as frictional charging occurs. This process involves the transfer of electrons between the two bodies, resulting in a redistribution of charges. Here's a detailed explanation of why the answer is option B:
1. Frictional charging: When two bodies are rubbed against each other, electrons are transferred from one body to another due to the friction between their surfaces. This transfer of electrons leads to a buildup of charges on the bodies.
2. Equal charges: The transferred electrons cause the bodies to acquire equal charges. This means that the number of positive charges on one body is equal to the number of negative charges on the other body.
3. Opposite charges: The acquired charges on the bodies are opposite in nature. This means that if one body gains a positive charge, the other body gains a negative charge.
4. Conservation of charge: The total charge in a closed system is conserved. Therefore, the total charge of the two bodies after rubbing remains zero, even though individual charges may be nonzero.
5. Coulomb's law: The acquired charges on the bodies result in an attractive force between them, which follows Coulomb's law. According to Coulomb's law, opposite charges attract each other, while similar charges repel each other.
Based on the above explanation, it is clear that when two bodies are rubbed against each other, they acquire equal and opposite charges (option B).

Explanation:
When it comes to charges, there are two types: positive and negative. Like charges refer to charges that are of the same type, either positive or negative.
The statement says "Like charges always repel each other." Let's break down the options and determine the correct answer:
A.

Always attract each other: This statement is incorrect because like charges do not attract each other. Instead, they repel each other.

B.

Sometimes attract each other: This statement is incorrect because like charges never attract each other.

C.

Always repel each other: This statement is correct. Like charges always repel each other. This is due to the electromagnetic force between the charges.

D.

Sometimes attract and sometimes repel each other: This statement is incorrect because like charges never attract each other. They always repel.

Therefore, the correct answer is C: Like charges always repel each other.

Intensity of an earthquake is measured on the Richter scale.
The Richter scale is a logarithmic scale that measures the intensity of earthquakes. It was developed by Charles F. Richter in 1935 and is still widely used today. Here is a detailed explanation of the Richter scale and how it measures earthquake intensity:
1. What is the Richter scale?
- The Richter scale is a numerical scale that assigns a magnitude value to an earthquake.
- It measures the amount of energy released by an earthquake at its source.
- The scale is logarithmic, meaning that each whole number increase on the scale represents a tenfold increase in the amplitude of the seismic waves.
2. How is the Richter scale calculated?
- The scale is based on the amplitude of seismic waves recorded by seismographs.
- Seismographs measure the ground motion caused by an earthquake.
- The amplitude of these waves is used to calculate the earthquake's magnitude on the Richter scale.
3. What do the Richter scale values represent?
- The Richter scale values range from 0 to 10 or higher.
- Each whole number increase on the scale represents a tenfold increase in the amplitude of the seismic waves and approximately 31.6 times more energy released.
- An earthquake with a magnitude of 2.0 or less is considered minor and is typically not felt by people.
- An earthquake with a magnitude of 7.0 or higher is considered major and can cause widespread damage.
4. Limitations of the Richter scale:
- The Richter scale is most accurate for earthquakes with magnitudes between 3.0 and 7.0.
- It is less accurate for very small or very large earthquakes.
- The scale does not take into account the duration or intensity of shaking or the potential damage caused by an earthquake.
In conclusion, the intensity of an earthquake is measured on the Richter scale, which is a logarithmic scale that measures the amplitude of seismic waves. The Richter scale provides a numerical value that represents the energy released by an earthquake at its source.

The brilliant flash of light produced in the sky is followed by

The flash of light produced in the sky refers to lightning. Lightning is a natural electrical discharge that occurs during thunderstorms. After the brilliant flash of light, several events can follow:

• Rain: Lightning often occurs during thunderstorms, which are usually accompanied by rainfall. Therefore, it is common for rain to follow the flash of light in the sky.


• Snow: In colder climates, lightning can occur during snowstorms. In such cases, the flash of light may be followed by snowfall.


• Hail: Hail is a form of frozen precipitation that can occur during severe thunderstorms. If the flash of light is followed by the sound of hail hitting the ground, then hail may be the subsequent event.


• Thunder: Lightning is always followed by thunder. Thunder is the sound produced by the rapid expansion and contraction of air surrounding a lightning bolt. Therefore, the brilliant flash of light is always followed by the rumbling sound of thunder.

So, the correct answer is D: Thunder.

The solid hard crust of the earth is called lithosphere.
Explanation:
The lithosphere is the outermost layer of the Earth's structure, encompassing the crust and a portion of the upper mantle. It is composed of solid rock and is relatively rigid compared to the underlying layers. Here's a detailed explanation of each option:
A. Biosphere:
- The biosphere refers to the part of the Earth where living organisms exist, including the land, water bodies, and the atmosphere.
- It includes all the ecosystems and the organisms within them.
B. Lithosphere:
- The lithosphere is the solid, outermost layer of the Earth.
- It includes the crust and a portion of the upper mantle.
- The lithosphere is broken into tectonic plates, which are constantly moving and interacting with each other.
C. Magma:
- Magma is molten rock that is found beneath the Earth's surface.
- It is formed from the melting of rocks within the mantle.
- Magma can erupt from volcanoes as lava.
D. Lava:
- Lava is molten rock that has reached the Earth's surface.
- It is typically associated with volcanic eruptions.
- When lava cools and solidifies, it can form new rock structures.
In conclusion, the solid hard crust of the earth is called the lithosphere. It is the outermost layer of the Earth's structure, consisting of solid rock and encompassing the crust and a portion of the upper mantle.

Charging a Body:
There are several ways to charge a body, including:
Friction:
- When two objects rub against each other, electrons can be transferred from one object to another.
- The object that gains electrons becomes negatively charged, while the object that loses electrons becomes positively charged.
- This is known as charging by friction.
Induction:
- Induction is a method of charging without direct contact between the charging object and the charged object.
- When a charged object is brought near a neutral object, the charges in the neutral object rearrange.
- This causes one side of the object to become positively charged and the other side to become negatively charged.
Conduction:
- Conduction involves direct contact between a charged object and a neutral object.
- When the two objects come into contact, electrons can be transferred from the charged object to the neutral object.
- This results in both objects having the same charge.
All of these methods:
- All of the above methods can be used to charge a body.
- Friction, induction, and conduction are all ways in which electrons can be transferred between objects, resulting in a charged body.
Therefore, the correct answer is D: all of these methods can be used to charge a body.

Explanation:
Charging a body refers to the transfer of electric charge to or from the body. There are several ways in which a body can be charged:
1. Rubbing it against another body: When two objects are rubbed together, electrons can be transferred from one object to another. This transfer of electrons leads to one object becoming positively charged, while the other becomes negatively charged. For example, rubbing a plastic comb against a woolen cloth can charge the comb.
2. Touching it to a charged body: When a neutral body comes into contact with a charged body, some of the charge from the charged body can transfer to the neutral body. This results in the neutral body becoming charged with the same type of charge as the charged body. For example, touching a neutral metal object to a positively charged object can result in the metal object becoming positively charged.
3. Bringing a charged body near it: When a charged body is brought close to a neutral body, the charges in the neutral body can be rearranged. This can result in one side of the neutral body becoming positively charged, while the other side becomes negatively charged. For example, bringing a negatively charged balloon close to a neutral wall can cause the wall to become polarized, with one side attracting the balloon and the other side repelling it.
Therefore, all of the above methods - rubbing, touching, and bringing a charged body near another body - can result in the charging of the body. The correct answer is option D.

The Earth's lithosphere and tectonic plates
The Earth's lithosphere is composed of several tectonic plates, which are large, rigid pieces of the Earth's crust and upper mantle. These plates are constantly moving and interacting with each other, resulting in various geologic phenomena such as earthquakes, volcanic activity, and the formation of mountain ranges.
Number of tectonic plates in the Earth's lithosphere
The exact number of tectonic plates is still a topic of ongoing scientific research and debate. However, the most widely accepted theory suggests that there are approximately 20 major tectonic plates on Earth. These plates vary in size, shape, and location, and they cover the entire surface of the Earth, including both land and ocean areas.
Importance of tectonic plates
The movement and interaction of tectonic plates play a crucial role in shaping the Earth's surface and influencing the distribution of continents, oceans, and geological features. Some key points regarding the importance of tectonic plates include:
- Plate tectonics is responsible for the formation of mountain ranges, such as the Himalayas, Andes, and Rockies.
- Tectonic activity leads to the occurrence of earthquakes and volcanic eruptions, which can have significant impacts on human populations and the environment.
- Plate boundaries are areas where tectonic plates meet and interact, creating features like subduction zones, transform faults, and mid-ocean ridges.
- Plate tectonics also plays a role in the cycling of Earth's materials, including the movement of carbon, water, and other elements through the lithosphere, hydrosphere, and atmosphere.
Conclusion
The Earth's lithosphere is composed of approximately 20 tectonic plates, which are responsible for shaping the Earth's surface and influencing various geological processes. The study of plate tectonics is crucial for understanding the dynamic nature of our planet and predicting natural hazards such as earthquakes and volcanic eruptions.

Lightning conductor is used to protect tall buildings from lightning flashes.
The lightning conductor, also known as a lightning rod, is a device used to protect tall buildings from the destructive power of lightning strikes. It works by providing a path of least resistance for the lightning to follow, diverting the electrical charge away from the building and safely into the ground. Here are the reasons why a lightning conductor is used specifically for protecting tall buildings from lightning flashes:
1. Dissipating the electrical charge:
- A lightning conductor is designed to capture the electrical charge from a lightning strike and conduct it safely to the ground.
- By providing a conductive path, it helps to prevent the lightning from striking the building directly and causing damage.
2. Preventing fire:
- When lightning strikes a building, it can cause fires due to the high temperatures generated.
- The lightning conductor redirects the lightning's electrical energy away from the building, reducing the risk of fire.
3. Protecting the structural integrity:
- Lightning strikes can have a devastating impact on the structural integrity of tall buildings.
- By providing a path for the lightning to follow, the lightning conductor helps to minimize the damage caused by the powerful electrical discharge.
4. Protecting the occupants:
- Lightning strikes can pose a significant risk to the people inside a building.
- A lightning conductor helps to protect the occupants by diverting the lightning's energy away from the building, reducing the chances of injury or electrocution.
5. Grounding the electrical charge:
- The lightning conductor is connected to a grounding system, which allows the electrical charge to safely dissipate into the ground.
- This grounding process helps to prevent electrical surges and potential damage to the building's electrical systems.
In conclusion, a lightning conductor is used to protect tall buildings from lightning flashes by providing a safe path for the electrical charge to follow and diverting it away from the building. This helps to prevent fires, protect the structural integrity of the building, and ensure the safety of its occupants.

Explanation:
To determine the intensity of an earthquake, we use the Richter scale, which measures the amplitude of seismic waves produced by the earthquake. The Richter scale is logarithmic, meaning that each whole number increase on the scale represents a tenfold increase in the amplitude of the seismic waves.
The intensity levels and their effects are as follows:
- Intensity 4.5 - 6.5: This is considered a moderate earthquake. It can cause slight damage to buildings and structures, but it is unlikely to result in the destruction of whole cities.
- Intensity 6.5 - 7.0: This is considered a strong earthquake. It can cause damage to buildings and structures, and in some cases, it may result in the destruction of poorly constructed or vulnerable structures.
- Intensity 7.0 - 7.9: This is considered a major earthquake. It can cause serious damage to buildings and structures, and in some cases, it may result in the destruction of well-built structures. However, it is still unlikely to destroy whole cities.
- Intensity 8 or above: This is considered a great earthquake. It can cause severe damage to buildings and structures, and in some cases, it can result in the destruction of whole cities.
Therefore, the correct answer is Option D: 8 or above. An earthquake of this intensity has the potential to destroy whole cities.