Question

Sound

Notes and Important notes
Class 9
Science​ .

Answer 1

Answer:

Chemical Reactions and Equations: Balanced and unbalanced chemical equations and balancing of chemical equations.

What is a chemical reaction Class 10?

Chemical Reaction: The transformation of chemical substance into another chemical substance is known as Chemical Reaction. For example: Rusting of iron, the setting of milk into curd, digestion of food, respiration, etc.

In a chemical reaction, a new substance is formed which is completely different in properties from the original substance, so in a chemical reaction, a chemical change takes place.

Only a rearrangement of atoms takes place in a chemical reaction.

The substances which take part in a chemical reaction are called reactants.

The new substances produced as a result of a chemical reaction are called products.

Example: The burning of magnesium in the air to form magnesium oxide is an example of a chemical reaction.

2Mg(s) + O2(g) △→ 2MgO(s)

Before burning in air, the magnesium ribbon is cleaned by rubbing with sandpaper.

This is done to remove the protective layer of basic magnesium carbonate from the surface of the magnesium ribbon.

Reactant: Substances which take part in a chemical reaction are called reactants.

Example: Mg and O2.

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Answer 2

Answer :

Sound waves :-

• They are mechanical waves.
• They require a material medium for propagation.
• They cannot travel in vaccum.
• The speed of sound is 330 m/s in air.
• In air, these waves are longitudinal.

When a body vibrates and it reaches us through the vibrations of the particles of the surrounding medium. Thus, sound requires a material medium for propagation.

Learn these :-

• The maximum displacement of the particle of the medium on either side of its mean position is called amplitude (a).
• The time taken by the particle of medium to complete its one vibration is called as time period (t).
• The number of vibrations made by a vibrating particle in one second is called as frequency (f).
• The distance travelled by a wave in one time period of vibration of particle of medium is called as wavelength (λ).
• The distance travelled by a wave in one second is called as wave velocity (V).

Relations :-

• V = fλ
• f = 1/T