Unit 1: Scientific Investigation
The Scientific Method
Making an Observation
Critically examine natural phenomena as they occur
Proposing a Hypothesis
Suggest a possible explanation for observations
Designing an Experiment
Plan methodology and identify variables
Types of Variables
Investigation Structure
- Aim: Clear experiment objective
- Apparatus: List all equipment needed
- Procedure: Step-by-step method
- Results: Tables and graphs
- Analysis: Discuss trends and patterns
Key Strategies
Safety: Follow all precautions
Equipment: Choose appropriate tools
Reliability: Take repeated readings
Analysis: Calculate averages
Sample Investigation: Water Expansion When Freezing
Apparatus
- • Two identical measuring cylinders
- • 20 cm³ water each
- • Refrigerator
Method
- 1. Fill cylinders to 20 cm³ mark
- 2. Place one in freezer, one in fridge
- 3. Observe volume changes
Conclusion
Water expands when it freezes into ice, as evidenced by increased volume in the frozen cylinder.
Unit 2: Thermal Expansion
Key Definitions
Expansion
The increase in size of a substance when heated
Contraction
The decrease in size of a substance when cooled
States of Matter
Thermal Expansion Experiments
Expansion in Solids
APPARATUS
Metal rod, rollers, pointer, heat source, G-clamp
OBSERVATION
Pointer deflects clockwise when heated, anticlockwise when cooled
CONCLUSION
Solids expand on heating and contract on cooling
Expansion in Liquids
APPARATUS
Glass flask, colored water, rubber stopper, glass tubing, Bunsen burner
OBSERVATION
Water level initially drops, then rises higher than before when heated
CONCLUSION
Liquids expand when heated due to molecular movement
Expansion in Gases
APPARATUS
Thin glass flask, rubber stopper, narrow glass tube, water
OBSERVATION
Water level drops and bubbles escape when heated; rises when cooled
CONCLUSION
Gases expand most when heated due to increased molecular motion
Applications of Thermal Expansion
🌡️ Electric Thermostats
Bimetallic strips maintain steady temperatures in irons, refrigerators, and incubators
🔩 Industrial Rivets
Hot rivets cool and contract, pulling steel plates tightly together
🔧 Expansion Joints
Allow pipes carrying steam/hot water to expand without damage
📞 Cable Fitting
Telephone and electricity cables fitted loosely for cold weather contraction
🚂 Railway Gaps
Gaps between rails prevent buckling in hot weather
🌉 Bridge Rollers
Steel/concrete bridges on rollers allow free temperature movement
⚠️ Effects of Sudden Temperature Changes
Harmful Effects:
- • Eggs can crack from sudden temperature changes
- • Stones can break from thermal shock
- • Drinking glasses crack when hot liquid is poured in
Solution:
Pyrex glass is made to withstand temperature changes by expanding and contracting uniformly, preventing cracking.