Solved Examples & Activities

Example 1: Understanding Air Composition

Question: If you have a room filled with 100 balloons representing the air molecules, how many balloons would be Nitrogen and how many would be Oxygen?

Solution: Based on the composition of air:

• Nitrogen constitutes 78%.
• Oxygen constitutes 21%.
• Other gases constitute 1%.

Therefore:

• 78 balloons would be Nitrogen.
• 21 balloons would be Oxygen.
• 1 balloon would represent Argon, Carbon Dioxide, and others.

Example 2: Soil Analysis

Activity: A student collected three soil samples:

1. Sample A: Sandy and dry.
2. Sample B: Dark, damp, and contains rotting leaves.
3. Sample C: Hard and lumpy.

Analysis:

• Sample A: likely from a desert or playground (low nutrient, low water retention).
• Sample B: likely forest or garden soil (High in humus/nutrients, good for plants).
• Sample C: likely clay or construction site soil (Compact, holds water but no air).

Conclusion: Sample B is best for growing the vegetables mentioned in the chapter because it contains humus (rotting leaves) and moisture.

Example 3: Energy Conversion

Question: Trace the energy transformation when a girl rides a bicycle.

Step-by-Step Flow:

1. Sun: Provides light/energy to crops (wheat/rice).
2. Crops: Store solar energy as chemical energy (food).
3. Girl: Eats the food. Her body converts chemical energy to muscular energy.
4. Bicycle: The girl uses muscular energy to pedal, creating mechanical (kinetic) energy to move the bike.

Example 4: Calculating Wastage

Problem: A dripping tap wastes 10 ml of water every minute. How much water is wasted in 1 hour? How much in 1 day?

Solution:

• Wastage per minute: 10 ml.
• Wastage in 1 hour (60 minutes): $10 \text{ ml} \times 60 = 600 \text{ ml}$
• Wastage in 1 day (24 hours): $600 \text{ ml} \times 24 = 14,400 \text{ ml}$

Conclusion: A single dripping tap can waste 14.4 Liters of water in a day! This highlights why fixing leaks is crucial.