NCERT Summary: Heat

# Heat Summary Class 7 NCERT Summary Chapter 3

### Hot and Cold

• The measure of degree of hotness or coldness of a substance is called its temperature.
• The device that is used to measure the temperature of a substance is called thermometer.

### Measuring Temperature

Thermometers are of two types:

• Clinical thermometer: Used for measuring temperature of human body.
• Laboratory thermometer: Used for measuring temperature of common objects.

• The temperature range of clinical thermometer is 35ºC to 42°C and that of laboratory thermometer is -10ºC to 110ºC. The unit for temperature is °C.

Step 1: Note the temperature difference indicated between the two bigger marks.
Step 2: Note down the number of divisions between these marks. If there are five divisions between them the, one small division can read 1/5 = 0.2°C
Step 3: Wash the thermometer with an antiseptic solution and give it a few jerks while holding firmly. Ensure that the level of mercury falls below 35°C.
Step 4: Now place the bulb of the thermometer under your tongue. Take the thermometer out after one minute and note the reading. This is your body temperature. The temperature should always be stated with its unit, °C.

• The normal temperature of human body is 37°C.
• The two most commonly used scales in which temperature is read are the Celsius scale and Fahrenheit scale.

Precaution for clinical thermometer

• Do not use a clinical thermometer for measuring the temperature of any object other than the human body.
• Also avoid keeping the thermometer in the sun or near a flame. It may break.

Precaution for laboratory thermometer

• In addition to the precautions needed while reading a clinical thermometer, the laboratory thermometer should be kept upright not tilted.
• Bulb should be surrounded from all sides by the substance of which the temperature is to be measured. The bulb should not touch the surface of the container.

### Transfer of Heat

1. Conduction: The transfer of heat in solids usually takes place by this method. Substances that allow heat to pass through them quite easily are called conductors and those that do not, are called insulators.
• The substances that allow heat to pass through them are called conductors of heat. Iron, copper, and aluminium are examples of conductors.
• The substances that do not allow heat to pass through them are called poor conductors of heat or insulators. Plastic and wood are examples of insulators.
2. Convection: The transfer of heat in liquids and gases takes place by convection. Land breeze and sea breeze are a result of unequal heating of air present over land and sea by the sun.
3. Radiation: Transfer of heat by radiation requires no medium. Heating of earth by sun is an example of heat transfer by radiation.

Sea Breeze

• The people living in the coastal areas experience an interesting phenomenon. During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up.
• The cooler air from the sea rushes in towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea is called the sea breeze.

### Land Breeze

• At night it is exactly the reverse. The water cools down more slowly than the land. So, the cool air from the land moves towards the sea. This is called the land breeze.

### Kinds of clothes we wear in winter and Summer

• Dark surfaces absorb more heat and, therefore, we feel comfortable with dark coloured clothes in the winter.
• Light coloured clothes reflect most of the heat that falls on them and, therefore, we feel more comfortable wearing them in the summer.
• In the winter, we use woollen clothes. Wool is a poor conductor of heat. The air get trapped in between the wool fibres. This air prevents the flow of heat from our body to the cold surroundings which make us feel warm.
The document Heat Summary Class 7 NCERT Summary Chapter 3 is a part of the Class 7 Course Science Class 7.
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## FAQs on Heat Summary Class 7 NCERT Summary Chapter 3

 1. What is heat?
Ans. Heat is a form of energy that is transferred between objects or systems due to a temperature difference. It flows from a hotter object to a cooler object until both reach the same temperature.
 2. How is heat transferred?
Ans. Heat can be transferred through three main processes: conduction, convection, and radiation. Conduction involves the direct transfer of heat through physical contact, convection occurs through the movement of fluids or gases, and radiation involves the emission and absorption of electromagnetic waves.
 3. What are the effects of heat on objects?
Ans. Heat can have various effects on objects. It can cause objects to expand or contract, change their physical state (such as melting or boiling), or increase their temperature. Excessive heat can also lead to structural damage or even combustion in certain materials.
 4. How is heat measured?
Ans. Heat is measured in units of energy, such as joules or calories. In scientific contexts, the SI unit for heat is the joule (J). However, the calorie (cal) is also commonly used, especially in the field of nutrition, where it represents the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius.
 5. What is the difference between heat and temperature?
Ans. Heat and temperature are related but distinct concepts. Heat refers to the transfer of energy, while temperature measures the average kinetic energy of particles in a substance. In other words, heat is the energy in transit, while temperature is a measure of how hot or cold an object is.

## Science Class 7

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