Thursday, November 29, 2012

Earthquake: Some Natural Phenomenon:CBSE Class 8th Science

Q. What are tectonic plates? 

Ans: The earth's lithosphere (crust) is fragmented into many pieces of stabs or plate of rocks called tectonic plates. These plates are in continuous motion i.e. they float over hot magma. 

Q. What is the term used to describe the fraction along earth crust?

Ans: Faults

Q. What do you call the point where an earthquake originates?

Ans: Focus or hypocenter

Q. Where is the intensity of tremor (vibrations) highest?

Ans: At the boundaries of the tectonic plates along fault.

Q. What do you call point on the earth surface that lies directly above the focus of an earthquake?

Ans: Epicenter

Q. Name the three layer of earth.

Ans: Crust, Mental and Core

Q. List two places in India which are most threatened by earthquake.

Ans: Two places in India which are most threatened by earthquake are

1. Kashmir       2. Rann of Kutch.

Q. What are the scientists who study about Earthquake called?

Ans: Seismologists

Q. Explain focus and Epicenter with respect to Earthquake?

Ans: The place below earth surface from where the earthquake originates is called the hypocenter  or  the  focus  of an earthquake. It is often several kilometers below the earth’s surface.  The spot on the earth’s surface exactly above the hypocenter of an earthquake is the epicenter.

Q. Define these terms.

Ans: (a) Seismograph: A type of instrument used to measure earthquake.

(b) Seismic wave: The shock wave produced by earthquake.

(c) Seismology: The branch of science deeling with earthquake and related problem is called Seismology.

(d) Tectonic plate: The crust layer of earth is made up of a number of rocky slabs called tectonic plates.

Q. What do you do in following situation during earthquake

Ans: (a) You are sitting in film theatre --->  stay on seat and cover your head with arm

(b) You are at home watching TV->     Do not go to another room. Take shelter under a table and protect your head by wrapping your arms around it

(c) You are travelling in car: -->       Drive slowly and do not come out till the tremors stop.

(d) You are in the basement of a building-->  Take shelter under a table and protect your head by wrapping 
your arms around it

Q. What is earthquake? How it is caused?

Ans: Ans: An earthquake is a sudden shaking or trembling of the earth lasting for a very short time.

Earthquake is caused due to the movement of tectonic plates that float over molten magma. As the 
plate moves collide, moves apart or slide over one another cause vibration that reach over surface of the 
earth and felt as earthquake.

Q. Describe the scale commonly used to measure the magnitude of earthquake?

Ans:  The magnitude of most earthquakes is measured on the Richter scale. The Richter magnitudes are  based on a logarithmic scale (base 10). Each whole number you go up on the Richter scale, the amplitude of  the ground motion recorded by a seismograph goes up ten times.

Q. What preventive steps should be taken to minimize the effects of earthquakes in future?

Ans: (a) We should build earthquake resistance building

(b) In earthquake prone area, light –weighted materials are used to build building

(c) Always take care to make sure ceiling fan, air conditioner etc fixed firmly.

Q. What are the after effects of earthquakes?

Ans: (a) Huge loss of life and property

(b) Fire may cause by inflammable material

(c) Sewer system may burst open

(d) Dams and embankments develop cracks

(d)In hilly are land slides

(e) Under ocean generate huge surface wave called Tsunami

Q. Fill in the blanks

(a) The intensity of an earthquake is measure on the -------------   ------------------

Ans: Richter scale

(b)------------- is a huge wave due to an earthquake occurring under the sea floor.

Ans: Tsunami

(c) earthquake are cause because of the motion of the ------- plates in the outer crust of the earth.

Ans: Tectonic

(d) Shock wave of earthquake are called --------------

Ans Seismic wave

(e) An earthquake of magnitude 2-4 on Richter scale is a  ---------------  one

Ans: weaker

(f) An earthquake of magnitude 8 or more on Richter scale is a  ---------------  one

Ans: stronger

(g)The instrument used to measure earthquake wave is called --------------.

Ans: seismograph

(i)The intensity of tremors is highest near the -------------

Ans: fault zoneorepicenter

(j) The intensity of tremors ----------- with distance from the epicenter.

1 comment:

Janardan Sunil said...

It consists of a vertical metal rod housed in a box, with two thin gold leaves attached to its bottom end.
working= When a charged object touches the metal knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of divergence is an indicator of the amount of charge.The white paper strips is used to explain the working of the apparatus. We fold the strips into half so that we make a mark of fold.We open the strip and iron it lightly with the mountain fold up.We hold the strip by pinching it at the fold.We notice that the two halves move apart.This shows that the strip has acquired charge on ironing. When we fold it into half, both the halves have the same charge. Hence they repel each other. The same effect is seen in the leaf electroscope.
On charging the curtain rod by touching the ball end with an electrified body, charge is transferred to the curtain rod and the attached aluminium foil. Both the halves of the foil get similar charge and therefore repel each other. The divergence in the leaves depends on the amount of charge on them.

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