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Answer:
(a) Some materials expand on heating and some contract on cooling. Heating makes the particles (that form the material) expand or become loose. Cooling makes the particles (that form the material) contract or become tight.
The amount of expansion differs in solids, liquids, and gases. Gases expand the most while solids expand the least. Table shows some examples of expansion.
Answer:
a) Some materials expand on heating and some contract on cooling. Heating makes the particles (that form the material) expand or become loose. Cooling makes the particles (that form the material) contract or become tight.
The amount of expansion differs in solids, liquids, and gases. Gases expand the most while solids expand the least. Table shows some examples of expansion.
Expansion in solids
Expansion in liquids
Expansion in gases
Railway tracks consist of two parallel metal rails joined together. Small gaps, called expansion gaps, are deliberately left between the rails as there is an expansion of the rails in hot weather.
Expansion and Contraction in Solids, Liquids and Gases 1
Water expands on heating. Try this with the help of an adult. Take a glass filled with water to its brim. Pour the water into a container and heat It (do not boil). Now try to pour the water back into the same glass. The water overflows.
Expansion and Contraction in Solids, Liquids and Gases 2
If you keep an inflated balloon in the sun for some time, what will happen? It will grow in size as the air inside it expands on taking heat from the surroundings.
Expansion and Contraction in Solids, Liquids and Gases 3
Cooling does the opposite of heating. Cooling causes a material to contract. Solids contract the least while gases contract the most. Table lists some examples of contraction.
Contraction in solids
Contraction in liquids
Contraction in gases
If we hold a very hot glass tumbler under cold water, it cracks. This is because the outer surface of the glass comes in direct contact with cold water and contracts more as compared to the inner surface.
Expansion and Contraction in Solids, Liquids and Gases 4
We observed that water expanded on heating. Can you say what will happen if the water is allowed to cool down and then poured back into the glass? Would it still overflow? No. This is because of contraction.
Expansion and Contraction in Solids, Liquids and Gases 5
If an inflated balloon is tied at the mouth of a bottle and the bottle is placed in ice-cold water, what will happen? The balloon will shrink in size, as the air inside the balloon contracts on cooling.
Expansion and Contraction in Solids, Liquids and Gases 6
Applications of Expansion and Contraction
Expansion by heating can be used in several everyday activities.
b)What is Silver?
A lustrous, soft white metal, silver is one of the elements that make up the Earth. Silver is found in nature as an elemental metal in its metallic form and combined with other elements such as sulfide, chloride and nitrate. Pure silver has a bright metallic white-gray color; silver nitrate and silver chloride are powdery white in color, while silver sulfide and silver oxide are dark gray to black.
Silver is stable in pure air and water, though it tarnishes quickly when exposed to air that contains elevated levels of ozone, hydrogen sulfide or sulfur. (In the past 200 years, the amount of sulfur in the atmosphere has increased, so silver tarnishes more quickly than it did in pre-Industrial times.) Tarnish can easily be removed, however, and does not destroy the metal the way oxidation process known as rust destroys iron. The fact that silver is otherwise impervious to the elements helps define it as a precious metal.
Silver is a rare metal that has long been valued for its versatility. Slag dumps in Asia Minor and the Aegean Sea islands show that our ancestors were mining silver over 5,000 years ago.
c) Fruit turns brown when exposed to air because a reaction is happening when a cut piece of fruit is exposed to oxygen. ... The chemical reaction can be simplified to: Polyphenol Oxidase + O2 → Melanin (Brown Color) Oxygen activates the compound polyphenol oxidase in the fruit to turn the fruit brown.
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