# Question 1

What is static electricity?

Solution:
The electrical charges generated by rubbing is called static electricity because these charges do not move.

# Question 2

What is the cause of lightning?

Solution:
Lightning is due to the meeting of the negative charges from the clouds and the positive charges on the ground.

# Question 3

What is a lightning rod? How it protects the buildings?

Solution:
Lightning rod is a device used to secure tall buildings from the effect of lightning. A metallic rod taller than the height of the building to be protected is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is fixed in the ground. This provides easy route for transfer of electric discharge to the ground. Several such rods would be required to safeguard a building with a large area.

# Question 4

What are the causes of earthquakes? Explain.

Solution:
We know that the tremors are caused by the disturbance deep down inside the uppermost layer of the earth, called the crust.

The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. Whey they brush against one another, or collide, or a plate goes under or moves away from another, they cause disturbance in the earth's crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

# Question 5

What is seismograph? Explain its construction and functioning.

Solution:
The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph the instrument is simply a vibrating rod, or a pendulum which starts vibrating when tremors occur. A pen is attached to the vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves scientist can construct a complete map of the earthquake and they can also estimate the energy associate with the earthquake which determines is power to cause destruction.

# Question 6

How the power of an earthquake is estimated? At what strength it becomes destructive?

Solution:
The power of an earthquake is expressed in terms of magnitudes on a scale called richter scale. Really destructive earthquake have magnitudes higher than about 7 on the richter scale. But bhuj and kashmir earthquakes had magnitudes greater than 7.5.

Like many other scales in science (decibel is another example) richter scale is not linear. This means that an earthquake of magnitude 6 does not have twice the destructive energy of an earthquake of magnitude 3. In fact, an increase of 2 in magnitude means 1000 times more destructive energy. For example an earthquake of magnitude 6 has thousand times more energy that an earthquake of magnitude 4.

# Question 7

If an earthquake's strength was 9.9 what would happen?

Solution:
The largest earthquake was a 9.5 event along the coast of Chile in 1960. The second largest was a 9.2 along the southern coast of Alaska in 1964. A 9.9 earthquake would be 4/10 of a unit larger than that of Chile, so it would release 10 raised to the power (1.5*4/10) = 4 times as much energy. The fault length would also be about 4 times longer, or 4,000 km. Although we don't expect an earthquake of this size, one of the places it might conceivably occur would be along the Aleutian/Alaska subduction zone. This would require the entire zone to rupture in one earthquake, which we don't think has ever happened. Such an earthquake would both cause strong shaking for 5 minutes or more as well as generate a large ocean wave (tsunami) that would travel at 800 km/hour across the entire Pacific Ocean. This wave could would have low amplitude over the open ocean but would grow in height as it reached shorelines and could cause a lot of damage to near shore facilities and homes.

# Question 8

If there was an earthquake in your house what should you do?

Solution:

Earthquakes

If you are indoors during an earthquake, keep calm and take cover under a heavy table or desk. Stay away from glass, windows or anything that could fall, like a bookcase.

If you are outdoors, move away from buildings, street lights and utility wires.

If you are in a crowded public place, do NOT rush for the doors. Everyone will be doing that. Instead, take cover under something heavy and stay away from things that could fall on you. Stay calm. Do not get in an elevator during an earthquake!

After an earthquake, be prepared for after shocks. After shocks are follow-up earthquakes that are usually smaller than the first one. They are dangerous because they can cause things that are weakened in the first earthquake to fall down.

If you are home and you smell gas or hear a hissing or blowing sound, open a window and get out of the building right away. It may mean that a gas line in your house has been broken. Tell your parent or another adult.

Make sure you are wearing shoes after an earthquake. There may be broken glass on the ground and inside your home.

If you are scared, share your fears with an adult. Earthquakes can be scary, but remember -- they only last a few seconds.

# Question 9

Are there more earthquakes under the sea than land?

Solution:
Areas of subduction, where an oceanic plate is sinking down into the Earth, are the sources of much of the World's earthquakes. Hence, more earthquakes occur under the sea than under the land.

# Question 10

If you fell into a crack caused by an earthquake where would you land?

Solution:
Cracks in the Earth caused by earthquakes are not very deep. If you fell into one, chances are that you could just stand up and climb out. Falling into a crack is the absolutely least likely way that you could be injured by an earthquake. For the most part it's buildings and other man-made structures that cause injury during an earthquake.