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The circum-pacific belt is also called Pacific ‘Ring of Fire’. This belt experiences greater number of volcanoes.

The volcanoes of the world are found certain areas. They are closely related to regions of folding and faulting and are found near the sea coast and islands. Most of the volcanoes are found in three belts:

i. Circum pacific belt 

ii. Mid continental belt 

iii. Mid Atlantic belt.

i. Circum pacific belt: The greatest concentration of volcanoes is found in this belt. It accounts for about two thirds of the world’s volcanoes. So it is also known as “Pacific ring of fire”. This belt starts form New Zealand, continues northwards into New Guinea, Indonesia, Philippines, coastal china, Japan, Kamchatka and Aleutian islands.

ii. Mid continental belt: This belt consist of Italy, Spain, France, Greece, turkey, Iran, Baluchistan, Myanmar and finally ends inn the eastern part of India.

iii. Mid Atlantic Belt: It includes the western part of India and islands east Atlantic Ocean. It extends form ice land t St. Helena including Madeira, Ascension Island, Cape Verde islands, Canary Island, St. Vincent and Azores. Besides a few volcanoes are also found in the Indian ocean Mauritius Madagascar and in the rift valley region of Africa, consisting of Kilimanjaro. 

Number of remaining children = 24 − 4 = 20

Let the number of sweets which each of the 20 students will get, be x.

The following table is obtained.

If the number of students is lesser, then each student will get more number of sweets.

Since this is a case of inverse proportion,

24 × 5 = 20 × x

x = (24 x 5)/20 = 6

Hence, each student will get 6 sweets.

Basic lava and Acidic lava are the two types of Lava.

Barren and Norcondom Island located to the northeast of port Blair of Andaman Islands.

(c) 5.5 grams per cubic cm

Correct Answer is: (c) L waves

The scientific study of volcano is known as ‘Volcanology’ 

Lines drawn on the map to show the places experiencing the same time of occurrence of earthquakes.

The Person who is specialized in the study of earthquakes are called Seismologist. 

Stromboli is known as ‘Lighthouse of the Mediterranean’.

(c) Science studying earthquake

• Richter scale 
• Mercalli Scale

Lines drawn on the map to show the places experiencing the same intensity of earthquake.

Lines drawn on the map to show the places recording the same time of occurrence of earthquake.

Narcondam in Andaman & Nicobar Islands is also an important volcano of India. 

The science of study of earthquakes is called seismology. 

Secondary waves are called transverse waves.

Charles Richter of U.S.A in invented Richter scale in 1935.

The surface waves or Long wave are most destructive as they vibrate much.

A large sea wave occasionally experienced along the sea coast caused by an underwater or sub-marine earthquake is called Tsunami.

Lithosphere, Pyrosphre and the core are the three concentric zones of the earth.

It means Vibration of the earth crust. The shaking or sudden vibration or series of vibrations are resulted from sudden movements of the earth’s crust.

It is the science which studies various aspects of seismic waves generated during the occurrence of earthquakes.

There are three major waves 

1. Primary waves (P) 

2. Secondary waves (S) and Surface waves (L).

Surface waves (long period waves) are most destructive earthquake wave.

The Circum-pacific belt record more seismic activities in the world.

These are the waves of greater height produced by the earthquakes in the oceans. Tsunami is a Japanese term. Tsu means port and nami means waves. Thus waves approaching the port are called Tsunamis. 

Elastic rebound theory was propounded by Harry Fielding Reid, and American Geologist in 1911.

Seismograph is used to record seismic waves.

Violent eruptions and extrusion of igneous magma from below the earth. Volcanic earthquakes are caused by gas explosions or the undoming and fissuring of volcanic structures. Such earthquakes bccur either simultaneously with eruptions or more commonly in the period preceding an eruption

A cone-shaped hill formed by of volcanic ash that is built up around a volcanic vent is called ash cone. 

In India, the seismograph centers are located at Kodaikanal (T.N), Poona, Kolaba (Maharashtra) Kolkata (W.B) and Gowribidnur (Karnataka).

An instrument devised to record and measure the intensity of earthquake is known as ‘seismograph’.

The outer portion or top layer of the crust is made up of granite rocks in which silica and aluminum elements predominate is known as Sial.

These are the slowest waves and reach the Epicentre at the Last stage. Surface waves are also called ‘Long’ waves of ‘Long period’ waves. The speed of these waves is around 3 to4 km per second and are confined to the upper layer of the crust. These waves cause heavy destruction and damage on the crust of the Earth.

The lower part of the earth’s crust is named as ‘Sima’ As it consists of Silica and Magnesium.

The earthquake waves are recorded by an instrument known as seismograph.

The temperature inside the Earth increases with the increasing depth (1°C per 32m) Formation of magma because of increase in temperature and reduction in pressure.

Dormant volcanoes are those volcanoes which have remained inactive for a long period of time, but may erupt in the future e.g. Mt Fuiyama in Japan.

Avogadro’s-Hypothesis and its applications:

In 1811, Italian physicist and mathematician Anedeo Avogadro published a hypothesis (also termed Avogadro’s law or principle) states that the volume of a gas is directly proportional to the number of molecules of the gas. This is represented by the formula ,
V = aN,
where a is a constant, V is the volume of the gas, and N is the number of gas molecules.
Applications
Avogadro’s law has been useful in substantiating a number of important laws and concepts. It has helped in the following areas:

(i) In explaining Gay Lussac’s law of gaseous volumes.

(ii) In determining the atomicity of gases.

(iii) In determining the molecular formula of a gas.

(iv) In establishing the relationship between relative molecular mass and vapour density.

Mt. Popa of Myanmar

1. v 

2. iv 

3. i 

4. ii 

5. iii

Extinct volcanoes are volcanoes which will most probably not erupt again in the future. Vesuvius and Krakatoa are example of extinct explosions. Popa in Myanmar (Burma) also is an example of extinct volcano.

Correct option is (d) Iron – nickel

Various types of landforms are produced by the volcanoes. They can be grouped into

1. Extrusive landforms 

2. Intrusive landforms

1. Extrusive landforms: The landforms which have been formed due to the accumulation and solidification of lava and other materials given out by volcanoes are known as extrusive landforms. The important extrusive land forms are:

a. Volcanic cones: volcanic cones are the most typical form of extrusive features or landforms.

The lava and other ejected materials that reach the surface of the earth are accumulated around the crater, and cones are formed. The formation of cones depends jupon the nature of explosion and the materials emitted out of it. There fore, cones are various types. They are:

• Cinder cones: A volcanic cone formed by volcanic cinder accumulated around the crates is called cinder cone. 
• Ash cone: A cone shaped hill formed by of volcanic ash that is built up around a volcanic ent is called ash cone. 
• Composite cone: A volcanic cone composed of alternative layers of ash, cinder and lava is called composite cone. 
• Parasite cone: Some times, many smaller cones are developed in the neighborhood of the main cone. They are called parasite cone. 

b. Crater: A crater is pit at the top of volcanic vent, during volcanic eruption, materials form the top of the cone are blown off and a bowl shaped depression is formed. It is known as crater. Caldera: Sometime a violent explosion blow away the original cone and forms a large basin-shaped depression called caldera 

Volcanic spine: The acid lava, which is vicious, solidifies quickly and blocks the vent. This stands up as a steep-sided cone called spine or plug.

Lava dome: The shape of lava dome is determined by the nature of lava. The highly fluid basic lava builds up shield dome with gently rising slopes, and flattened top. The basic lava, which is highly viscous, builds up dome with a great height and steep slope 

Lava plateau: An extensive elevated land made up of depositional lava called lava plateau. 

2. Intrusive land forms: Intrusive landforms occur when lava solidifies with the earth’s. crust and gives rise to various shapes or forms. Intrusive landforms are formed along the bedding planes of sedimentary rocks. There are various forms of intrusive landforms. They are:

Dyke: The Magma from the interior of the earth finds its way towards the surface through a passage. When it is able to reach the surface, it cools and solidifies, and a vertical or highly inclined feature is formed, and such a features is called dyke.

Sill: A sheet of magma which lies along the bedding plan is called sill. Laccolith: Laccolith is a large mound of igneous rock formed along a bedding plane in the sedimentary rock layers.

Batholith: Batholith is a very large dome – shaped intrusion of igneous rock. It is exposed to the surface only after considerable erosion.

Hot springs or thermal spring’s are more common. The water sinks deep inside where the rocks are heated. The heated water rises to the surface without any explosion. Such springs contain dissolved minerals which are of medicinal value. They can be also used to generate electricity. Iceland has thousands of hot springs. A Geyser is a hot spring form which a column of hot water and stream are alternatively ejected to a great height.

1. Shield volcano 

2. Mt. Fujiyama 

3. St.Helena

A volcano is a vent or an opening in the earth’s crust through which hot magma erupts from deep below the surface. The opening is usually circular in form.

Some of the volcanoes are characterized with both explosive and tranquil eruptions. These are intermediary volcanoes as they are named after their mode of eruption. Since the materials thrown out are different, they posses both the qualities. Some time solid fragments are thrown with explosion, whereas sometimes only lava flows out silently. As such the slope of the hills formed with the deposition is also of intermediately.