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Do You Know
Q1. Evaporation is a Surface Phenomenon
Description
The correct answer is Surface phenomenon. Evaporation is the process in which a liquid changes into vapor from its surface at any temperature below its boiling point. Only the particles present on the surface of the liquid escape into the air, so evaporation is called a surface phenomenon.
In evaporation, particles at the surface gain enough energy to overcome the attractive force between molecules and move into the air as vapor. This process happens slowly and continuously.
Easy Explanation
When wet clothes dry under sunlight or even in normal air, water changes into vapor from the surface of the clothes. The entire liquid does not change at once. Only the particles on the top surface escape first. That is why evaporation is called a surface phenomenon.
Step-by-Step Understanding
Step 1: A liquid contains many moving particles.
Step 2: Surface particles have more freedom to move.
Step 3: Some particles gain enough energy from surroundings.
Step 4: These particles escape into the air as vapor.
Step 5: Gradually, the liquid evaporates.
Factors Affecting Evaporation
- Temperature
Higher temperature increases evaporation because particles gain more energy. - Surface Area
Larger surface area increases evaporation because more particles are exposed. - Wind Speed
Fast-moving air removes water vapor quickly and increases evaporation. - Humidity
Low humidity increases evaporation because air can hold more vapor.
Difference Between Evaporation and Boiling
- Evaporation happens only at the surface.
- Boiling happens throughout the liquid.
- Evaporation occurs at any temperature.
- Boiling occurs at a fixed boiling point.
Examples
- Drying of wet clothes.
- Sweat cooling the body.
Key Points
- Evaporation is a surface phenomenon.
- It occurs below boiling point.
- Surface particles escape into air.
- It causes cooling effect.
- Faster in hot and windy conditions.
Q2. SI Unit of Power is Watt
Description
The correct answer is Watt. Power is the rate at which work is done or energy is transferred. The SI unit of power is watt (W).
If a machine does work quickly, it has greater power. Power helps us understand how fast energy is used.
Formula of Power
Power = Work Done / Time Taken
P = W / t
Where:
- P = Power
- W = Work Done
- t = Time
Understanding the Formula
Suppose a machine does 100 joules of work in 10 seconds.
P = 100 / 10
P = 10 Watt
This means the machine uses or transfers energy at the rate of 10 joules per second.
Easy Explanation
Two students may climb stairs of the same height. If one student climbs faster, that student uses more power because the work is completed in less time.
Step-by-Step Understanding
Step 1: Work is done when force moves an object.
Step 2: Time taken to complete work is measured.
Step 3: Divide work by time.
Step 4: The result gives power.
Step 5: SI unit of power is watt.
Relation Between Watt and Joule
1 Watt = 1 Joule/second
This means one watt of power is used when one joule of work is done in one second.
Examples
- Electric bulb ratings like 60 W or 100 W.
- Fans, motors, and heaters use power.
Key Points
- Power measures speed of doing work.
- SI unit is watt.
- Formula: P = W/t
- 1 watt = 1 joule per second.
- More power means faster work.
Q3. Proton has Positive Charge
Description
The correct answer is Positive charge. A proton is a positively charged subatomic particle found inside the nucleus of an atom.
Atoms contain three important particles:
- Proton
- Neutron
- Electron
Among these, protons carry positive charge, electrons carry negative charge, and neutrons have no charge.
Easy Explanation
The nucleus of an atom contains protons and neutrons. Protons help identify the element because the number of protons decides the atomic number.
For example:
- Hydrogen has 1 proton.
- Carbon has 6 protons.
- Oxygen has 8 protons.
Step-by-Step Understanding
Step 1: Atoms are made of tiny particles.
Step 2: Protons are present in the nucleus.
Step 3: Protons carry positive charge.
Step 4: Electrons carry negative charge.
Step 5: Equal protons and electrons make atoms neutral.
Charge of Proton
A proton carries a charge of +1.
Why Positive Charge is Important
- It attracts electrons.
- Helps maintain atomic structure.
- Determines atomic number.
Examples
- Hydrogen nucleus contains one proton.
- Sodium atom contains 11 protons.
Key Points
- Proton is positively charged.
- Located inside nucleus.
- Charge value is +1.
- Determines atomic number.
- Important for atomic stability.
Q4. Velocity Includes Direction
Description
The correct answer is Direction. Velocity is speed in a particular direction. It is a vector quantity because it has both magnitude and direction.
Speed only tells how fast an object moves, but velocity tells both how fast and in which direction it moves.
Easy Explanation
If a car moves at 60 km/h, that is speed.
If a car moves at 60 km/h towards the north, that is velocity.
Direction is what makes velocity different from speed.
Formula of Velocity
Velocity = Displacement / Time
v = s / t
Where:
- v = Velocity
- s = Displacement
- t = Time
Understanding the Formula
Suppose a person moves 100 meters east in 20 seconds.
v = 100 / 20
v = 5 m/s east
Direction “east” must be included because velocity needs direction.
Step-by-Step Understanding
Step 1: Measure displacement.
Step 2: Measure time taken.
Step 3: Divide displacement by time.
Step 4: Add direction to the answer.
Step 5: Final value becomes velocity.
Difference Between Speed and Velocity
Speed: Scalar quantity, no direction.
Velocity: Vector quantity, includes direction.
Examples
- Train moving at 80 km/h northward.
- Wind blowing towards west at 20 km/h.
Key Points
- Velocity includes direction.
- It is a vector quantity.
- Formula: Velocity = Displacement/Time
- Different from speed.
- Direction is necessary in velocity.
Q5. Phloem Carries Food
Description
The correct answer is Food. Phloem is a plant tissue responsible for transporting prepared food from leaves to all parts of the plant.
Plants prepare food through photosynthesis in leaves. This food must reach roots, stems, flowers, and fruits. Phloem performs this transport.
Easy Explanation
Leaves are called the food factories of plants. After making food, the plant needs to send it everywhere for growth and energy. Phloem works like a transport system that carries food throughout the plant body.
Step-by-Step Understanding
Step 1: Leaves prepare food by photosynthesis.
Step 2: Food is converted into soluble substances.
Step 3: Phloem tissues absorb this food.
Step 4: Food moves to different plant parts.
Step 5: Plant gets energy and nutrition.
Structure of Phloem
Phloem contains:
- Sieve tubes
- Companion cells
- Phloem fibers
- Phloem parenchyma
Difference Between Xylem and Phloem
Xylem: Carries water and minerals.
Phloem: Carries food.
Examples
- Sugar prepared in leaves reaches roots.
- Fruits receive nutrients through phloem.
Key Points
- Phloem transports food.
- Food moves from leaves to plant parts.
- Works in both upward and downward directions.
- Important for plant growth.
- Different from xylem.
Quick Revision Notes
Evaporation
- Surface phenomenon.
- Causes cooling.
- Faster in high temperature and wind.
Power
- SI unit = Watt.
- Formula: P = W/t.
- 1 watt = 1 joule/second.
Proton
- Positive charge.
- Present in nucleus.
- Determines atomic number.
Velocity
- Includes direction.
- Vector quantity.
- Formula: Velocity = Displacement/Time.
Phloem
- Carries food in plants.
- Food prepared in leaves.
- Essential for plant nutrition.