Some natural phenomena

Q1) What type of charges can an object possess?

Ans:

An object can possess positive or negative charge. The object which loses electrons becomes positively charged and the other which gains electrons becomes negatively charged.

Q2) what can you do to make hard rubber positively charged?

Ans:

When hard rubber is rubbed with polyester, hard rubber becomes positively charged.

Q3) list the methods by which objects can be charged?

Ans:

Objects can be charged by :

      1-   Friction

      2-  Conduction

      3-  Induction

    

Q4) what are the huge rocky plates that cover the entire earth called?

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The huge rocky plates that cover the entire earth are called  the tectonic plates.

Q5) name the outermost layer of the earth?

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The outermost layer of the earth is called the crust.

Q6) what is the core of the earth made up of?

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The core of the earth is made up of solid metal . (iron and nickel)

Q7) what moves the tectonic plates?

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The semi-solid layer that is present in the mantle of the earth is made up of molten rock ( magma). This layer is in motion all the time due to which the tectonic plates which float over this keep moving.

Q8) what causes an earthquake?

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As the magma moves, it moves the tectonic plates that float on it. At times, the adjacent tectonic plates collide with each other. This causes an earthquake.

Q9) What will happen if a plastic ruler rubbed against a woolen garment is brought close to bits of paper? Why?

Ans:

When plastic ruler rubbed against a woolen garment, the woolen garment will lose electrons and acquires a positive charge. The electrons which are lost from the woolen garment will flow into the plastic ruler. As a result the plastic ruler becomes negatively charged. Both the woolen garment and the plastic ruler will acquire static electricity. So, when the plastic ruler is brought close to bits of paper, the paper gets attracted to it.

Q10) illustrate attraction and repulsion between charged bodies.

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Q11) what is thunder? How is it created?

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During thunderstorm, the negative charge from the cloud attracts the positive charge from the land. This forms a continuous path through which charge from the cloud flows down and causes lightning. The sudden heating expands the air violently, and then contract it. This creates a sound which is known as thunder.

Q12) How are convection currents formed in magma?

Ans:

There is a temperature difference between the outer and the inner mantle. The outer mantle is cool since it meets the colder, solid crust above it. The inner mantle gets hotter due to the very hot core beneath it. These differences in the temperature between the outer and inner mantle gives rise to a movement called convection currents in the fluid magma.

Q13) What is the difference between hypocenter and epicenter?

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The spot where the earthquake originates is called the hypocenter or the focus of an earthquake. The spot on the earth’s surface exactly above the hypocenter of an earthquake is the epicenter.

Q14) List two safety measures you would take during an earthquake?

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i)           Move to an open area immediately

ii)         Stay away from buildings, electric poles, trees, sign boards, bridges or any other man made structure.

Q15) describe the working of a simple electroscope.

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Materials required a glass jar, a metal plate, a one holed cork, metal rod, two stripes of aluminium foil.

A simple electroscope is set up as shown. When you rub a plastic ruler on your dry hair and touch it to the metal plate, the strips repel each other and open out because they acquire the negative charge of the ruler by conduction. The opening out of the aluminium strips indicates that the object which was brought in contact was charged. This is the most simple type of electroscope.

Q16) Explain how lighting occurs?

Ans:

During thunderstorms, the negative charge from the cloud attracts the positive charge from the land. This forms a continuous path through which large amount of negative charge which is accumulated in the clouds rushes down this path, giving rise to huge amount of electricity. The sudden rush of electrical charge heats up the air to about 20,000 C, producing a bright glow of lightning. This is how lightning strike take place.