Heat.pdf 7th Class Science samyans academy chapter notes

What is Heat?

Heat is a form of energy that transfers from one body to another due to a temperature difference. It is a measure of the thermal energy of a system.


Types of Heat:

1. Sensible Heat: Heat that changes the temperature of a substance.
2. Latent Heat: Heat that changes the state of a substance (solid to liquid or liquid to gas).


Heat Transfer Methods:

1. Conduction: Direct transfer of heat between particles.
2. Convection: Transfer of heat through fluids.
3. Radiation: Transfer of heat through electromagnetic waves.


Effects of Heat:

1. Expansion
2. Melting
3. Boiling
4. Changes in state
5. Chemical reactions


Units of Heat:

1. Joule (J)
2. Calorie (cal)
3. Kilocalorie (kcal)


Heat-Related Concepts:

1. Temperature
2. Thermal equilibrium
3. Specific heat capacity
4. Heat capacity
5. Thermal conductivity


Real-Life Applications:

1. Cooking
2. Refrigeration
3. Air conditioning
4. Industrial processes
5. Thermoelectric devices


Key Terms:

1. Heat
2. Temperature
3. Thermal energy
4. Conduction
5. Convection
6. Radiation


Examples:

1. Heat transfer from a stove to a pot.
2. Heat from the sun warming the Earth.
3. Heat from a fire melting ice.


This description provides a comprehensive overview of heat, covering its definition, types, transfer methods, effects, units, and applications.

1. Heat
Everyday Experience
We encounter heat in our everyday
lives, from a cup of hot coffee to a
warm summer day.
A Form of Energy
Heat is a form of energy that can be
transferred from one object to
another.
Heat and Us
Heat plays a crucial role in our lives,
influencing our comfort, our energy
sources, and our environment.
By K Sandeep swamy

2. Hot and Cold
Woollen clothes
keep us warm in
winter.
The material traps heat,
providing insulation and
warmth.
Cotton clothes feel
cool in summer.
Cotton allows for better
airflow, helping to
dissipate heat and keep
us cool.
We can determine if
an object is hot or
cold by touching it.
However, this method isn't
always reliable because
our perception of
temperature can be
subjective.
Temperature is a
more accurate
measure of how hot
or cold an object is.
It provides a numerical
value that objectively
indicates the degree of
hotness or coldness.

3. Measuring Temperature
Clinical Thermometer
Measures body temperature from
35°C to 42°C
Reading a Thermometer
Note temperature difference
between larger marks
Wash thermometer with antiseptic
before and after use
Normal Body Temperature
Average of 37°C, can vary slightly
Do not use for non-body
temperature

4. Measuring Temperature
with a Laboratory
Thermometer
1
Observe the Thermometer
Note the range and smallest division
2
Immerse the Bulb
Dip the thermometer in water, avoiding the sides
3
Read the Temperature
Wait for the mercury to stabilize, then note the reading
4
Precautions
Keep the thermometer upright, bulb fully surrounded

5. Clinical Thermometer
A clinical thermometer is a medical instrument used to measure body
temperature. It has a digital display that shows the temperature reading.

6. Activity: Reading a Thermometer
Observe the Thermometer
Examine the clinical thermometer
and identify the different parts.
Read the Temperature
Place the thermometer under your
tongue and wait for the reading.
Record the Temperature
Note the temperature displayed on
the thermometer and record it.

7. Precautions for using a
clinical thermometer
Proper Placement
Ensure the thermometer is placed correctly for an accurate reading.
Timing
Wait the recommended time for the thermometer to provide a reliable
result.
Hygiene
Clean the thermometer before and after use to prevent the spread of
germs.

8. Radiation: How Heat Travels Without a
Medium
Heat Transfer by Radiation
Heat can be transferred without a
medium, like when sitting in front of
a room heater.
Cooling by Radiation
Hot objects cool down by radiating
heat to the surroundings.
Blocking Radiant Heat
Using an umbrella can block radiant
heat from the sun.

9. Activity: Measuring temperature with a
laboratory thermometer
1
Fill container
Fill a container with hot water
2
Insert thermometer
Carefully insert a laboratory thermometer
3
Read temperature
Observe and record the temperature reading
In this activity, we will use a laboratory thermometer to measure the temperature of hot water. First, fill a container
with hot water. Then, carefully insert the laboratory thermometer into the water. Finally, observe and record the
temperature reading on the thermometer.

10. Differences between clinical and laboratory
thermometers
Celsius Scale
Measures temperature in degrees Celsius
Insulator
Clinical thermometers have an insulating casing

11. Conduction of Heat
1 Heat Transfer
2 Conduction
3 Wool Insulation
Wool is a poor conductor of heat, trapping air between its fibers to prevent heat flow from the body to the cold
surroundings.
Wearing wool clothes in winter keeps us warm by minimizing heat loss through conduction.

12. Convection of heat in water
1
Heating water
Heat energy is absorbed
2
Warm water rises
Cooler water sinks
3
Circulation occurs
Uniform heating of water
When water is heated, the heat energy is absorbed, causing the water molecules to move faster and become less
dense. This warm water then rises, while the cooler water sinks, creating a circular convection current that evenly
distributes the heat throughout the water.

13. Convection of Heat in Air
Warm Air Rises
Warm air expands and becomes
less dense, causing it to rise.
Convection in Gases
Heat transfer in gases like air
occurs through convection.
Cooler Air Sinks
As the warm air rises, cooler air
moves in to replace it.

14. Radiation: How heat travels without a
medium
Radiant Heat Transfer
Heat can travel through empty
space via electromagnetic waves
No Medium Required
Radiation does not need a physical
medium to transfer heat
Examples
Sunlight, heat lamps, and infrared
radiation

15. Effect of color on heat absorption
1
Dark colors
Absorb more heat
2
Light colors
Absorb less heat
3
Clothing
Dark clothes preferred in winter, light clothes in
summer
Darker colored objects absorb more heat than lighter colored objects. This is why in hot climates, it is advised to
paint the outer walls of houses white, as the light color will absorb less heat from the sun. Similarly, during winter,
people prefer to wear dark colored clothes as they absorb more body heat, while in summer, light colored clothes
are preferred to stay cooler.

16. Why Woollen Clothes Keep Us Warm
Insulation
Wool fibers trap air, providing
insulation to retain body heat.
Moisture Wicking
Wool absorbs and wicks away
sweat, keeping skin dry and warm.
Temperature Regulation
Wool adjusts to changes in body
temperature, keeping you
comfortable.

17. Summary of Key Concepts
Conduction of Heat
Observe how a paper strip does not
burn when wrapped around a
continuously rotating iron rod.
Convection of Heat
Observe how a paper spiral moves
when suspended above a candle
flame.
Thermal Expansion
Observe how hot water causes the
cold water bottle to rise when the
postcard is removed.
Discuss normal temperatures of domestic animals and birds with a veterinarian.

18. The Celsius Scale
The Celsius scale was devised by a Swedish astronomer, Anders Celsius
in 1742. He initially fixed the boiling point of water as 0°C and the
freezing point as 100°C, but this order was soon reversed.