Quick Revision Notes: Class 7 Science

Chapter: Heat

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### 1. Important Definitions (महत्वपूर्ण परिभाषाएं)

• Heat (ऊष्मा): A form of energy that flows from a body at a higher temperature to a body at a lower temperature. (ऊष्मा ऊर्जा का एक रूप है जो अधिक तापमान वाली वस्तु से कम तापमान वाली वस्तु की ओर प्रवाहित होती है।)
• Temperature (तापमान): A reliable measure of the hotness or coldness of an object. (किसी वस्तु की गर्द या ठंडेपन की माप को तापमान कहते हैं।)
• Thermometer (थर्मामीटर / तापमापी): A device used for measuring temperature. (तापमान मापने के लिए उपयोग किया जाने वाला उपकरण।)
• Conduction (चालन): The process by which heat is transferred from the hotter end to the colder end of an object. (वह प्रक्रिया जिसमें ऊष्मा किसी वस्तु के गर्म सिरे से ठंडे सिरे की ओर स्थानांतरित होती है।)
• Convection (संवहन): The transfer of heat by the actual movement of particles of a fluid (liquid or gas). (तरल पदार्थों में ऊष्मा का स्थानांतरण जिसमें कणों की वास्तविक गति होती है।)
• Radiation (विकिरण): The transfer of heat that does not require any medium. It travels in the form of waves. (ऊष्मा का वह स्थानांतरण जिसके लिए किसी माध्यम की आवश्यकता नहीं होती।)

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### 2. Key Concepts & Scales of Temperature (तापमान के पैमाने)

• Standard Unit of Temperature: Degree Celsius (°C)
• Clinical Thermometer:
  • Used to measure human body temperature.
  • Range: 35°C to 42°C (Normal human body temperature is 37°C or 98.6°F).
• Laboratory Thermometer:
  • Used to measure temperatures of other objects/water in labs.
  • Range: Usually -10°C to 110°C.

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### 3. Modes of Heat Transfer (ऊष्मा स्थानांतरण की विधियाँ)

Feature	Conduction (चालन)	Convection (संवहन)	Radiation (विकिरण)
Medium required?	Yes (Mostly Solids)	Yes (Liquids & Gases)	No (Can travel through vacuum)
How it works?	Particles vibrate and pass heat to neighbors.	Hot particles rise, cold particles sink to take their place.	Travels via electromagnetic waves (infrared).
Example	Heating an iron rod with a flame.	Boiling water, Sea and Land breezes.	Heat from the Sun reaching the Earth.

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### 4. Conductors and Insulators (चालक और रोधी)

• Conductors (सुचालक): Materials that allow heat to pass through them easily.
  • Examples: Aluminium, Iron, Copper, metals.
• Insulators / Poor Conductors (कुचालक): Materials that do not allow heat to pass through them easily.
  • Examples: Wood, Plastic, Air, Water.

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### 5. Natural Phenomena: Sea Breeze and Land Breeze (समुद्री समीर और थल समीर)

• Sea Breeze (समुद्र समीर - Day Time):
  • Land heats up faster than water. Air above land rises, and cooler air from the sea rushes towards the land.
• Land Breeze (थल समीर - Night Time):
  • Land cools down faster than water. Warm air from the sea rises, and cooler air from the land moves towards the sea.

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### 6. Clothing and Seasons (कपड़े और ऋतुएँ)

• Summer Clothes: Light-colored clothes are preferred because they reflect most of the heat that falls on them.
• Winter Clothes: Dark-colored clothes absorb more heat. Also, woolen clothes trap air between wool fibers. Air is a poor conductor of heat, which prevents body heat from escaping, keeping us warm.