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Do You Know
1. Evaporation
Evaporation is a process in which a liquid changes into vapor at any temperature, without reaching its boiling point. It happens only at the surface of the liquid and occurs slowly.
How it works:
Some particles of the liquid gain enough energy to escape from the surface and become gas.
Factors affecting evaporation:
- Higher temperature increases the rate
- Larger surface area speeds it up
- Faster air movement (wind) increases evaporation
- Lower humidity helps evaporation occur faster
Example: Sweat cools our body because it evaporates and takes heat away.
2. Density (SI Unit: kg/m³)
Density describes how much mass is present in a given volume of a substance.
Formula:
Density = Mass ÷ Volume
Simple idea:
If two objects are the same size but one is heavier, that one has greater density.
Why kg/m³?
Because mass is measured in kilograms and volume in cubic meters in the SI system.
Examples:
- Iron sinks in water because it has higher density
- Oil floats on water because it has lower density
3. Discovery of the Electron – J.J. Thomson
The electron was discovered by J.J. Thomson in 1897 through experiments using cathode rays.
What he did:
He passed electricity through a vacuum tube and observed rays coming from the cathode.
What he found:
- These rays were made of tiny negatively charged particles
- These particles were later named electrons
Importance:
This discovery proved that atoms are made of smaller particles and are not indivisible.
4. Uniform Acceleration
Uniform acceleration occurs when the velocity of an object changes by equal amounts in equal intervals of time.
In simple terms:
The speed increases or decreases at a steady and constant rate.
Formula:
Acceleration = Change in velocity ÷ Time
Graph:
A velocity-time graph shows a straight line in this case.
Examples:
- An object falling freely under gravity
- A vehicle increasing speed at a constant rate
5. Parenchyma Tissue
Parenchyma is a basic plant tissue made up of living cells. It is found in soft parts of plants.
Main functions:
- Storage of food and water
- Photosynthesis (if chlorophyll is present)
- Exchange of gases (if air spaces are present)
Structure:
- Thin cell walls
- Cells are loosely packed with spaces between them
Examples:
- Storage of starch in potatoes
- Photosynthesis in leaves