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SHORT ANSWER TYPE QUESTIONS

1.What is static electricity ?

Static electricity is the buildup of an electric charge on the surface of an object. This charge remains in one place (“static”) until it is released, often through a spark or a shock. It happens when two surfaces rub together and electrons are transferred from one to the other.

2. Why does a rubbed comb attract bits of paper ?
When a plastic comb is rubbed through dry hair, electrons are transferred, giving the comb a negative charge. This charged comb creates an electric field. When brought near neutral, light objects like paper bits, it attracts the positive charges within them, causing the paper to stick to the comb.

3. What are the two types of charge? On rubbing a glass rod with silk cloth, what type of charge is generated in (a) silk cloth, (b) glass rod?
The two types of electric charge are positive charge and negative charge.

When a glass rod is rubbed with a silk cloth:

• (a) Silk cloth gets a negative charge (it gains electrons from the glass).
• (b) Glass rod gets a positive charge (it loses electrons to the silk).
• Which scale measures the magnitude of an earthquake? How does this scale differ from other scales?

The Richter scale measures the magnitude (energy released) of an earthquake.
It differs from other scales (like the Mercalli Intensity Scale) because it measures the actual energy released at the source using scientific instruments (seismographs). Other scales often measure the earthquake’s effects or intensity (like damage to buildings and how people felt it) at different locations.

5. What is earthing ? Why is earthing necessary in household circuits?

Earthing (or grounding) is the process of connecting the metal casing of electrical appliances to the ground (earth) via a wire.

It is necessary for safety. If a loose live wire touches the metal casing, the current will flow directly into the ground through the earthing wire instead of passing through a person touching the appliance, preventing a severe electric shock.

6. What is a lightning conductor ?
A lightning conductor (or lightning rod) is a safety device used to protect tall buildings from lightning strikes. It is a metal rod installed at the highest point of a building, connected to the ground by a thick metal strip. It provides a safe, low-resistance path for the lightning’s electrical charge to travel directly into the earth, preventing damage to the structure.

7. What is the focus and epicentre of an earthquake ?

• Focus (Hypocenter): The point inside the Earth’s crust where an earthquake originates. This is where the rock first breaks and energy is released.
• Epicentre: The point on the Earth’s surface directly above the focus. The shaking is usually strongest at the epicentre.

LONG ANSWER TYPE QUESTIONS

1. What is an electroscope? How does it detect the charge ?

An electroscope is a simple scientific instrument used to detect the presence of an electric charge on a body.

It typically consists of a metal rod with a metal disc or ball at the top and two thin, lightweight metal leaves (often gold) at the bottom, enclosed in a glass jar.
How it works:

• When a charged object touches the metal disc, the charge flows down the metal rod to the leaves.
• Since both leaves receive the same type of charge (positive or negative), they repel each other and diverge (spread apart).
• The degree of divergence indicates the amount of charge. A stronger charge causes the leaves to spread wider.

2. How does lightning occur ?
Lightning is a giant spark of electricity in the atmosphere. It occurs due to the separation of charges inside a thundercloud.

• Charge Separation: Inside a storm cloud, strong updrafts cause ice particles and water droplets to collide. This process separates charges, leaving the top of the cloud positively charged and the bottom negatively charged.
• Electric Field: This creates a powerful electric field between the cloud and the ground, and within the cloud itself.
• Leader Stroke: When the electric field becomes strong enough, it ionizes the air, creating a conductive path called a stepped leader that zigzags towards the ground.
• Return Stroke: As the leader nears the ground, a powerful surge of positive charge travels up from tall objects to meet it. This connection completes the circuit, resulting in the bright, high-current flash of light we see as lightning. The rapid heating and expansion of air along this path creates the sound of thunder.

3. List some do’s and don’t’s during lightning.
DO’s:

• Seek shelter inside a substantial building or a fully enclosed, metal-topped vehicle.
• If indoors, avoid using corded electrical appliances, plumbing, and stay away from windows and doors.
• Crouch low if caught in an open field with no shelter, minimizing contact with the ground.
  DON’T’s:
• Do NOT stand under isolated tall trees, in open shelters, or on hilltops.
• Do NOT stay in or near water bodies like pools, lakes, or the beach.
• Do NOT hold metal objects like umbrellas or fishing rods.

4. How does a lightning conductor work ?
A lightning conductor works on the principle of providing a safe, preferred path for lightning to reach the ground.

1. The pointed metal rod at the top of the building attracts the lightning strike more easily than the building itself (principle of action of points).
2. When lightning strikes, it hits the rod.
3. The thick, low-resistance copper strip connected to the rod carries the massive electric current safely down the side of the building.
4. The other end of the strip is buried deep in a moist ground plate, which safely disperses the electrical energy into the earth, preventing fire or structural damage to the building.

5. What is the cause of an earthquake ? List some precautions to be taken during an earthquake.
Cause: Earthquakes are primarily caused by the sudden release of built-up energy along faults (cracks) in the Earth’s crust. This is usually due to the movement of the large tectonic plates that make up the Earth’s surface. Volcanic activity can also trigger earthquakes.
Precautions during an earthquake:

• DROP, COVER, and HOLD ON. Drop to your hands and knees, take cover under a sturdy table or desk, and hold on until the shaking stops.
• Stay away from windows, glass, and heavy objects that could fall.
• If you are outdoors, move to an open area away from buildings, trees, and utility wires.
• If you are in a vehicle, pull over to a clear spot and stay inside with your seatbelt on.
• Do not use elevators.

HIGHER ORDER THINKING SKILLS

1. If the cap of a gold-leaf electroscope is replaced by plastic in place of copper and a positively charged body is wiped across it, would the gold leaf diverge? Why or why not?

No, the gold leaf would not diverge.
This is because plastic is an insulator, while metals like copper are conductors. The function of the metal cap/disc is to receive the charge and conduct it down to the metal rod and leaves. When a charged body is wiped across a plastic cap, the charge cannot pass through the insulator to reach the leaves. The charge remains localized on the plastic surface, leaving the leaves uncharged and undeflected.

2. Why it is advised to use mud or timber instead of heavy construction material in earthquake-prone areas ?
It is advised to use lighter, more flexible materials like mud or timber in earthquake-prone areas because they are less rigid and have more flexibility.

• During an earthquake, the ground shakes. Heavy, rigid materials like stone or unreinforced concrete are brittle and cannot bend or sway with these forces. They are more likely to crack, crumble, or collapse.
• Materials like timber and mud are lighter, which means they impose less inertial force when shaken. Timber, in particular, has some natural flexibility (give), allowing the structure to absorb and dissipate some of the seismic energy without catastrophic failure, making it safer.