Скачать или смотреть NCERT Class 7th Science Chapter 4 HEAT | Introduction, Hot and Cold| Clinical Thermometer|

HEAT Class 7 Science Chapter 4: In today's Class 7 Science Sprint session in Chapter 4, we discuss HEAT.

Two types of thermometer:
1- Clinical thermometer: Thermometer means to measure our body temperature is called clinical thermometer.
2- Laboratory thermometer.

The temperature of an object: It is the degree of hotness or coldness of an object.

Thermometer: It is a device that can be used to find out how hot an object is. In other words, we use a thermometer to measure the temperature of an object.

Temperature is the degree of change of temperature and can be measured using a thermometer or a calorimeter. It is a means of determining the internal energy contained within the system.

Measuring the temperature of an object using a thermometer:
It is a device that is used to measure the body temperature of a person.
The Mercury level in the thermometer rises up in the thread-like portion of the thermometer which therefore indicates the temperature of the body.
The level of the Mercury can be measured by reading the scale given on the thermometer.
The scale of the thermometer records the temperature in degree Celsius, generally, 35o C to 45o C, which is the range of human body temperature.
On average, the temperature of the human body is around 37o C.
The clinical thermometer has a small sharp curve (kink) present near the bulb. This prevents the Mercury level from falling down on its own in the thermometer.

Hot and Cold:
We can understand if an object is hot or cold by the sense of touch. However, it can trick us sometimes. Therefore, we use a thermometer.

The transfer of heat class 7:
The flow of heat always takes place from and hot object to a cold object.
1- Conduction: The process of flow of heat from a hot object to a cold object is called Conduction. Some objects can conduct heat while others cannot.

2- Conductors: The objects that can allow the heat to flow through them are called Conductors. For Example, metals such as copper and aluminum.

3- Insulators: The objects that do not allow the flow of heat from them are called Insulators. For Example, Wood, and Plastic.

4- Convection: The transfer of heat in liquids and gases is called Convection. The molecules of the liquid or gases that are near the source of the heat get heated first. They become lighter due to the heat and move upwards. The colder particles being heavier take the place and this process continues until the whole liquid or the gas gets heated. That is why the area above the flame of a candle always feels hot but the area on the sides of the candle does not.

5- Radiation: It is a process of transfer of heat in the form of waves. For Example, the sun's heat reaches the Earth’s surface through radiation. Every hot object radiates some heat into the environment. Hence, many times an object gets heated just by being near to a hot object.

Effect of heat class 7 are:
Heat increase in temperature
Heat expands a substance
Heat changes the state
Heat brings chemical change.
Heat affects the living thing