Willer Academy
Nation Builders Through Education | Founded by Er. Rahul Kumar Dubey Sir
Chapter 4: Heat
Subject: Science (Physics)
Class: 7
Series: Base Builder for Moderate to Hard
Learning Objectives
By the end of this chapter, you, the future scientist and nation-builder, will be able to:
- Understand the concept of heat and temperature
- Differentiate between conduction, convection, and radiation
- Explain how heat transfer affects our daily lives
- Understand the working of thermometers and temperature scales
- Solve numerical problems related to heat and temperature
- Apply knowledge to real-life situations involving heat transfer
4.1 Introduction: What is Heat?
Heat is a form of energy that flows from a hotter object to a colder object. It's what makes things warm or hot. Temperature, on the other hand, is a measure of how hot or cold something is.
Quick Check
Touch a metal spoon and a wooden spoon that have been sitting in the same room. Which one feels colder? Why do you think that is?
4.2 Measuring Temperature
Temperature is measured using a thermometer. There are three common temperature scales:
Celsius Scale
0°C - Water freezes
100°C - Water boils
Fahrenheit Scale
32°F - Water freezes
212°F - Water boils
Kelvin Scale
273K - Water freezes
373K - Water boils
Numerical & Application 1: Temperature Conversion
- Scenario: Normal human body temperature is 37°C.
- Problem: What is this temperature in Fahrenheit? The formula is: °F = (°C × 9/5) + 32
- Solution:
- °F = (37 × 9/5) + 32
- °F = (66.6) + 32
- °F = 98.6°F
This is why we say normal body temperature is 98.6°F!
Task 1
Create a temperature conversion chart. List Celsius temperatures from 0 to 100 in increments of 10, and calculate their Fahrenheit equivalents using the formula.
4.3 Transfer of Heat
Heat can be transferred in three different ways:
Conduction
Heat transfer through direct contact. Example: Metal spoon in hot soup
Convection
Heat transfer through fluid movement. Example: Boiling water
Radiation
Heat transfer through electromagnetic waves. Example: Heat from the sun
Experiment: Heat Conduction
Take rods of different materials (iron, copper, aluminum, wood). Attach drawing pins to one end of each rod using wax. Heat the other end. Observe which pin falls first. This shows which material is the best conductor of heat.
Fastest
Copper
Fast
Aluminum
Medium
Iron
Slowest
Wood
4.4 Heat in Our Daily Lives
Understanding heat transfer helps us in many practical applications:
Insulators: Materials that don't allow heat to pass through easily
- Wood, plastic, wool, air
- Used in handles of cooking utensils, thermos flasks, winter clothing
Conductors: Materials that allow heat to pass through easily
- Metals like copper, aluminum, iron
- Used in cooking utensils, heat exchangers, radiators
Numerical & Application 2: Insulation Efficiency
- Scenario: A thermos flask reduces heat transfer by 90%. Hot tea at 80°C is kept in the flask.
- Problem: If the room temperature is 20°C, and without the flask the tea would cool to 30°C in 1 hour, what temperature will the tea be after 1 hour in the flask?
- Solution:
- Temperature drop without flask: 80°C - 30°C = 50°C
- With flask, heat transfer is reduced by 90%, so temperature drop is only 10% of 50°C = 5°C
- Final temperature = 80°C - 5°C = 75°C
This shows how effective insulation can keep things hot!
Task 2: Home Insulation
Survey your home and identify three places where insulation is used to prevent heat transfer. For each, note the material used and whether it's preventing heat loss or heat gain.
4.5 Sea Breeze and Land Breeze
The different heating rates of land and water cause local winds:
Sea Breeze: During the day, land heats up faster than water. The warm air over land rises, and cooler air from the sea moves in to take its place.
Land Breeze: At night, land cools down faster than water. The warm air over water rises, and cooler air from the land moves out to sea.
Experiment: Convection Currents
Fill a rectangular transparent container with water. Place a drop of food coloring at one end. Place an ice pack at that end and a hot water bottle at the other end. Observe how the color moves through the water, demonstrating convection currents.
Section B: MCQ Challenge (20 Questions)
Test your knowledge and find where you need to improve!
1. Which of these is the best conductor of heat?
a) Wood
b) Plastic
c) Copper
d) Air
2. Normal human body temperature is:
a) 100°C
b) 37°C
c) 0°C
d) 50°C
3. Heat from the sun reaches us by:
a) Conduction
b) Convection
c) Radiation
d) Both conduction and convection
4. Which material is a good insulator of heat?
a) Copper
b) Aluminum
c) Wood
d) Iron
5. The transfer of heat in a fluid by movement of particles is called:
a) Conduction
b) Radiation
c) Convection
d) Insulation
6. Which temperature scale uses 32°F as the freezing point of water?
a) Celsius
b) Kelvin
c) Fahrenheit
d) Rankine
7. Heat transfer by electromagnetic waves requires:
a) Medium
b) Vacuum
c) Both medium and vacuum
d) None
8. Boiling water in a pot demonstrates:
a) Conduction
b) Convection
c) Radiation
d) Evaporation only
9. Ice melting in a warm room is an example of:
a) Conduction
b) Convection
c) Radiation
d) All of the above
10. Heat is measured in which unit?
a) Celsius
b) Joule
c) Kelvin
d) Watt
11. Why do metals feel colder than wood at the same temperature?
a) Metals have lower density
b) Metals conduct heat faster than wood
c) Wood absorbs more heat
d) Wood is denser than metals
12. Which of the following is a poor conductor of heat?
a) Aluminum
b) Silver
c) Glass
d) Copper
13. Radiation of heat does not require:
a) Air
b) Vacuum
c) Space
d) Medium
14. In which case heat transfer is fastest?
a) Copper rod
b) Wooden rod
c) Plastic rod
d) Air
15. What is the freezing point of water in Celsius?
a) 0°C
b) 100°C
c) 32°C
d) -273°C
16. Heat transfer by conduction is maximum in:
a) Air
b) Water
c) Metals
d) Vacuum
17. Temperature is a measure of:
a) Heat content
b) Thermal energy
c) Average kinetic energy of particles
d) Conduction rate
18. Which breeze occurs during the day?
a) Land breeze
b) Sea breeze
c) Monsoon breeze
d) None
19. Which breeze occurs during the night?
a) Land breeze
b) Sea breeze
c) Cyclone breeze
d) None
20. Which material would you use to reduce heat loss in a house?
a) Aluminum sheets
b) Wool and foam insulation
c) Glass sheets
d) Metal rods
Answer Key: 1-c, 2-b, 3-c, 4-c, 5-c, 6-c, 7-b, 8-b, 9-a, 10-b, 11-b, 12-c, 13-d, 14-a, 15-a, 16-c, 17-c, 18-b, 19-a, 20-b
Section C: Answer in Detail (For Answer Writing Practice)
Q1. Explain the three methods of heat transfer with suitable examples from daily life.
Hint: Include conduction, convection, and radiation with specific examples.
Q2. Describe how a thermometer works. Why is mercury used in some thermometers?
Hint: Discuss thermal expansion and properties of mercury.
Q3. What are sea breeze and land breeze? Explain how they are formed.
Hint: Discuss differential heating of land and water.
Section D: Tackle These! (Higher Order Thinking Skills - HOTS)
Q1. If you were to design an energy-efficient house for Willer Academy's eco-project, what materials would you use for insulation and why? How would you minimize heat transfer in summer and winter?
Think about: Conductors, insulators, ventilation, and building orientation.
Q2. Why do people often use white or light-colored clothes in summer and dark-colored clothes in winter? Explain the science behind this practice.
Think about: Absorption and radiation of heat.
Q3. Design an experiment to compare the insulating properties of three different materials (e.g., wool, cotton, and foam). What materials would you need and how would you conduct the experiment?
Think about: Controlled variables, measurement techniques, and data recording.
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