Heat-Transfer-in-Nature.pdf/7th class new ncert/by k sandeep swamy/samyans eduhub ppt/notes/pdf

Absolutely, Sandeep! Here's your updated and detailed chapter notes for Class 7 NCERT Curiosity Science – Chapter: Heat Transfer in Nature, now including the definitions of conduction, convection, and radiation.

---

🌡️ Chapter 7: Heat Transfer in Nature – Detailed Notes

🔍 Introduction to Heat
- Heat is a form of energy that causes substances to become warmer.
- It flows from a hot object to a cold object until both reach the same temperature.
- The Sun is the primary source of heat energy for Earth.

---

🔁 Modes of Heat Transfer

🔹 Conduction
Definition:
Conduction is the transfer of heat through a solid material from one particle to another without the movement of the material itself.

Example:
A metal rod gets hot at one end when the other end is placed in a flame.

🔹 Convection
Definition:
Convection is the transfer of heat in fluids (liquids and gases) through the movement of the fluid itself, forming convection currents.

Example:
Warm air rising and cool air sinking in the atmosphere causes wind patterns.

🔹 Radiation
Definition:
Radiation is the transfer of heat in the form of electromagnetic waves, such as infrared rays, without needing a medium.

Example:
The Sun’s heat reaching Earth through space.

---

🌬️ Heat Transfer in Nature

🌊 Sea Breeze and Land Breeze
| Time | Process | Description |
|-----------|---------|-------------|
| Daytime | Sea Breeze | Land heats faster → hot air rises → cool air from sea replaces it |
| Nighttime | Land Breeze | Sea retains heat → hot air rises → cool air from land replaces it |

---

🏔️ Heat and Climate
- Equatorial regions receive direct sunlight → warmer climate.
- Polar regions receive slanted rays → colder climate.
- Coastal areas have moderate climate due to water’s high heat capacity.

---

🌡️ Measuring Temperature

- Temperature is the degree of hotness or coldness.
- Measured using a thermometer.
- Common units: Celsius (°C) and Fahrenheit (°F).

---

🧪 Activities and Observations

- Metal vs. Wood: Metal feels colder because it conducts heat away faster.
- Black vs. White Cloth: Black absorbs more heat; white reflects it.
- Hand over flame: You feel warmth due to radiation.

---

🧠 Key Terms

| Term | Definition |
|--------------|------------|
| Conduction | Heat transfer through solids |
| Convection | Heat transfer through fluids |
| Radiation | Heat transfer without medium |
| Insulator | Material that resists heat flow |
| Thermometer | Device to measure temperature |

---

🏠 Real-Life Applications

- Cooking utensils use metals for quick heat transfer.
- Thermos flasks use insulators to maintain temperature.
- Weather patterns are influenced by convection in air and water.
- Solar panels use radiation from the Sun to generate electricity.

---

1. Heat Transfer in Nature
Pema and her brother Palden live in Gangtok. One cold winter evening, they sit near a fireplace. Palden talks about his
trip to Kerala during winter. He says Kerala is warmer and more humid than Gangtok.
Their grandfather explains, "Kerala is closer to the equator and has a long coastline, so it is warmer and more humid."
Palden adds, "We learned that the Sun is the main source of heat and light, and places near the equator are usually
hot."

2. A Question About Cooking Utensils
While they talk, Pema watches her grandmother cooking
thukpa (a traditional Sikkimese dish) in a big metal pan. She
asks, "Why are cooking utensils usually made of metal?" Palden
answers, "Because metals are good conductors of heat," which
they studied in their science chapter.
Let's dive into nature of heat and its transfer in
nature!

3. Conduction of Heat
Conduction is the process by which heat is transferred from the hotter part of an object to its colder part
through direct contact. In solids, especially metals, particles vibrate when heated and pass this energy to
neighboring particles without moving from their positions. This makes conduction an important process in everyday
activities like cooking.
How Conduction Works
When one end of a metal object is heated, the particles at that end gain energy and vibrate more. These vibrations
are passed to adjacent particles, transferring heat along the object. For example, when a metal pan is heated, the heat
travels from the flame to the entire pan, making it hot.

4. Activity: Understanding Heat Conduction
Let us perform an activity to learn why certain materials are good conductors of heat.
Materials Needed
Metal strip (aluminium or iron), Four pins, Candle or spirit lamp, Stand (or two bricks for support), Wax to attach the
pins, Heat source
Steps
Take a metal strip (15 cm long) and attach four pins to it using wax, spaced about 2 cm apart.1.
Secure the strip to a stand or between two bricks.2.
Heat the end of the strip away from the stand with a candle or spirit lamp.3.
Observe and predict the behaviour of the pins.4.
Heat transfer in a metal strip

5. Observations and Conclusions
Prediction
You are asked to predict the order in which the pins will fall as the strip is heated.
Observation
The first pin (Pin I), closest to the candle flame, falls first, followed by the other pins in order (II, III, and IV). The reason
for the sequential fall of the pins is the process of heat conduction.
Conclusion
Conduction is the process of heat transfer from the hotter part of a material to the cooler part. As the heat
travels along the metal strip, it causes the wax holding each pin to melt, leading to the pin falling.
The heat is transferred from the hot end (near the flame) to the colder end through the metal particles vibrating
and passing on the energy to their neighbours.
Metals are good conductors of heat, which is why metal utensils are used for cooking.

6. Conductors and Insulators of Heat
Good Conductors of Heat
Metals (e.g., aluminium, iron) allow heat to pass
through them easily.
This is why metal cooking utensils are commonly
used.
Poor Conductors of Heat (Insulators)
Materials like wood, glass, clay, and porcelain do not
allow heat to pass through easily.
For example
Tea or coffee cups made of clay or porcelain help in retaining heat longer.
Woollen fabrics trap air, which is a poor conductor, and help keep us warm.
The presence of air between layers of clothing (such as woolen clothes or blankets) reduces heat flow and helps keep
us warm.
Air trapped between two thin blankets acts as an insulator

7. How Air Acts as an Insulator
1. Woollen Fabric and Heat Retention
Woollen fabric traps air in its tiny pores or gaps.
Since air is a poor conductor of heat, it reduces the flow of heat from our bodies to the cooler surroundings.
This trapped air acts as insulation, helping to keep us warm in cold weather.
Similarly, when multiple layers of clothing trap air between them, the air acts as an insulator and keeps the body
warm.
2. Blankets and Trapped Air
The presence of air between two thin blankets makes them warmer compared to a single thick blanket.
This is because the air layer between blankets slows down heat loss from our body, making us feel warm and cozy.

8. Insulated Houses and Hollow Bricks
3. Insulated Houses: Using Heat Transfer Principles
Is it possible to build houses that remain comfortable inside despite very hot or cold outside weather?
Yes, houses in extreme climates use the concept of heat transfer to stay warm in winter and cool in summer.
4. Hollow Bricks and Heat Insulation
Some houses use hollow bricks for their outer walls.
Air trapped inside the hollow parts of these bricks acts as a poor conductor of heat.
This trapped air helps keep the house warm in winters by reducing heat loss and cool in summers by reducing
heat gain.
Thus, hollow bricks help maintain a comfortable indoor temperature by slowing heat transfer through the walls.

9. Fascinating Facts: Himalayan Houses
The upper regions of the Himalayas, such as the Mori
block of Uttarkashi in Uttarakhand, experience
extremely cold climates and heavy snowfall in winters.
To keep houses warm in such harsh conditions, people
build walls with two wooden layers.
The space between these wooden layers is filled
with cow dung and mud.
Both wood and mud are poor conductors of heat,
meaning they do not allow heat to escape easily.
This natural insulation prevents heat loss, helping
keep the houses warm and cozy during winter.
Try yourself: What is conduction?
a. Heat transfer through liquids
b. Heat transfer through direct contact
c. Heat transfer through air
d. Heat transfer through radiation
View Solution

10. Convection
Convection is the process of heat transfer in liquids and gases, where heated particles move and carry heat
with them. This movement creates currents, such as breezes near the sea or the rising of smoke, making convection
a key process in nature.
How Convection Works?
When a liquid or gas is heated, its particles gain energy, become less dense, and rise.
Cooler, denser particles then move to take their place, creating a cycle of movement called a convection current.
For example, when water is heated in a pan, the warmer water rises, and cooler water sinks, distributing heat.
Convection in Gases: In air, heated air expands, becomes lighter, and rises.
For example: Smoke rises because it is made up of hot gases and tiny solid particles that are released when
something burns.
When these particles are heated, they become lighter than the surrounding air, causing them to rise.
This is similar to what happens when air is heated; it expands, takes up more space, and becomes less dense, which
is why warm air also rises.

11. Convection in Liquids
Convection in Liquids: In liquids like water, heated particles rise, and cooler ones sink, creating a circular flow.
To understand why smoke rises more clearly, let us perform an activity.
Materials Needed: paper cups, a wooden stick, threads, a burning candle.
Procedure
Hang the paper cups in an inverted position on the wooden stick using threads.
Place the stick horizontally.
Light a candle and place it under one of the cups.
Observe what happens to the cups.

12. Observations: Hot Air Rising
Observations and Explanation
The cup with the candle underneath it rises because the air inside the cup heats up.
When air is heated, it expands and takes up more space, making it lighter. This causes the cup to rise.
Hot air rising up
Example of Air Expansion
When a partially inflated balloon is placed in the Sun, the air inside it heats up and expands, causing the balloon to
become larger.
Smoke Rising
When an incense stick is burnt, the smoke produced is a mixture of hot gases and tiny solid particles.
Since the smoke is warmer than the surrounding air, it rises.

13. Activity: Convection in Water
To understand how heat transfer occurs in liquids, we can perform an activity.
Materials Needed: 500 mL beaker, water, straw, potassium permanganate, candle.
Procedure
Fill the beaker halfway with water.
Using a straw, place a grain of potassium permanganate at the center of the beaker's base.
Place a candle under the center of the beaker's base.
Observe the movement of the colored streak in the water.
Observations
As heat is supplied, a streak of color starts moving up from the center and coming down from the sides of the beaker.
Demonstration of convection in heated water

14. Understanding Land and Sea Breeze
Explanation
The water at the bottom of the beaker gets heated, becomes lighter due to expansion, and rises.
The cooler, heavier water from the sides then comes down to take its place.
This creates a continuous cycle until the entire volume of water is heated.
Conclusion
The movement of the colored streak in the water demonstrates convection, which is how heat transfer occurs in
liquids and gases - through the movement of particles. Just like air, water gets heated through convection, where
particles move from one place to another, carrying heat with them.
Land and Sea Breeze
During the day, the land near the beach heats up faster than the water in the sea. This is because different
materials absorb heat at different rates.
However, at night, the situation changes: the land cools down faster than the water.
This difference in how quickly land and water heat up and cool down is what causes the land and sea breeze.

15. Activity: Heating and Cooling Rates
Let us check how land and water get heated and cooled by performing an activity.
Materials Required: Two identical bowls, Soil, Water and Two laboratory thermometers
Procedure
On a clear, sunny day, under the supervision of a teacher or an adult, take two identical bowls.1.
Fill one bowl halfway with soil and the other bowl halfway with water.2.
Fix a laboratory thermometer in each bowl, ensuring that the bulbs are immersed in the soil and water,
respectively, and do not touch the bottoms or sides of the bowls.
3.
Place the set-up in sunlight.4.
Observe the rise in temperature of the soil and water over a period of time.5.
Observations
After 20 minutes, you will find that the temperature of the soil rises more than that of the water. This indicates that
the soil heats up faster than water.
Cooling Experiment
After letting the soil and water heat up, bring the set-up indoors and allow it to cool for 20 minutes.1.
Observe the cooling rates of the soil and water.2.
Conclusion
Soil heats up faster than water.
Soil also cools faster than water.

16. Sea Breeze and Land Breeze
Sea Breeze
During the day, when the land heats up quickly, the air
above the land also becomes warm and rises. This
creates a low-pressure area over the land. Meanwhile,
the air above the sea is cooler and denser. To fill the
low-pressure area over the land, the cooler air from
the sea moves in, creating a sea breeze. This is why
people living in coastal areas feel a refreshing breeze
coming from the sea during the day.
Land Breeze
At night, the land cools down faster than the sea. The
air above the land becomes cooler and denser,
creating a high-pressure area. Meanwhile, the air
above the sea is still relatively warm and rises, creating
a low-pressure area. To balance the pressure, the
cooler air from the land moves towards the sea,
creating a land breeze. This is why people living near
the shore experience a change in wind direction from
day to night.
Sea Breeze
Land Breeze
Try yourself: What happens to air when it is heated?
a. It becomes less dense and rises.
b. It becomes denser and sinks.
c. It cools down immediately.
d. It remains the same.
View Solution

17. Radiation
Radiation is heat transfer do not need any medium. All objects emit heat this way.
Heat transfer happens directly from the a hot object to us through a process called radiation.
For example, the Sun's heat reaches Earth by radiation. The Sun's hot surface (about 6000°C) emits energy waves,
some of which warm the Earth.
Radiation does not require a medium, which is why we can feel the warmth of the Sun even though space is a
vacuum.

18. Examples of Heat Transfer in Daily Life
Many everyday examples show conduction, convection, and radiation happening at the
same time.
For example, when water is heated in a pan:
01
Conduction
Heat moves from the flame to the
pan by conduction.
02
Convection
Water inside the pan heats up by
convection.
03
Radiation
The warmth we feel around the flame
and pan is due to radiation.
Fascinating Facts: The Himalayan Bukhari
In the upper Himalayan region, a traditional room heater called bukhari is used to keep rooms warm in winter. It is an
iron stove where wood or charcoal is burned. A long pipe attached at the top acts as a chimney to release smoke. The
flat top of the bukhari can also be used for cooking by placing utensils on it.
When the bukhari is used, all three types of heat transfer4conduction, convection, and radiation4work together to
warm the room and cook food.

19. The Water Cycle
Water exists in three states in nature
Liquid: in oceans, rivers, lakes
Solid: as snow, glaciers, ice sheets in mountains and polar regions
Gas: as water vapor in the atmosphere
During summer, snow and ice melt due to the Sun's radiation, forming rivers that flow into oceans. Fresh snow
replenishes the ice in winter.
Water in oceans, rivers, and lakes evaporates due to the Sun's heat. Plants also release water vapor through
transpiration.
Water vapor rises, cools, and condenses to form clouds. Clouds cause precipitation (rain, snow, hail).
This continuous movement of water4evaporation, condensation, precipitation, infiltration, and runoff4is called the
water cycle
Water cycle
Importance of Water Cycle
The water cycle is the process through which water continuously moves upward as water vapor and downward
through precipitation, passing through soil, rocks, and plants before returning to water bodies. This cycle helps to
redistribute and replenish water in rivers, lakes, and oceans while conserving the total amount of water on Earth.

20. Groundwater and Conservation
Know a Scientist: Varahamihira
Varahamihira was a famous astronomer and mathematician of the 6th century CE from Ujjaini (now Ujjain), Madhya
Pradesh. In his work Brihatsamhita, he described methods to predict seasonal rainfall. His predictions were based on
observations of cloud formation, wind patterns, the positions of stars and the moon, and other natural phenomena.
Seepage of Water Beneath the Earth's Surface
Let's First Perform Activity to understand: How does water seep through the surface of
the Earth?
Take three transparent, used plastic bottles of 1 L capacity.
Cut them in the middle and make a small hole in the cap of each bottle.
Keep them inverted and put some clay in one bottle, sand in the second, and gravel in the third.
Place three identical beakers below each bottle.
Add 200 mL of water to each bottle.
Predict the amount of water flowing out of each bottle.
Collect the water that flows through each bottle for 10 minutes.
Compare the amount of water that comes through each bottle.
An activity to compare the flow of water through clay, sand and gravel
You may have observed that water flows fastest through gravel, slower through sand, and slowest through clay. This is
due to the differences in the particle sizes and the spaces between them:
Gravel: The spaces between gravel particles are wider, allowing water to pass through quickly.
Sand: The particles are smaller than gravel, so the spaces are narrower, causing slower water flow.
Clay: The smallest particles create very tight spaces, restricting water flow the most.