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Question I wonder how heat from the fire reaches us? (Page 96)
The heat from the fire reaches us through the process of radiation. In this process, heat is transferred by radiating energy to the surroundings. Heat transfer by radiation does not require any medium.
Chapter 3: Heat
Heat is a form of energy that flows from hot to cold. Temperature measures hotness/coldness. Clinical thermometer (35-42 degrees C, has kink) and laboratory thermometer (-10 to 110 degrees C, no kink) are used for measurement. Heat transfers by conduction (solids), convection (liquids/gases), and radiation (no medium needed). Dark surfaces absorb more heat; light surfaces reflect more.
Theme: Physics | Difficulty: Age-appropriate for Class VII
Key Formulas & Equations
| Formula / Equation | When to Use |
|---|---|
| Normal body temperature = 37°C | Reference value |
| Clinical range: 35°C – 42°C | For body temperature only |
| Lab thermometer range: −10°C to 110°C | For experiments |
Must-Know Concepts
- Heat is energy (joules); temperature is degree of hotness (°C)
- Clinical thermometer has a kink; lab thermometer does not
- Conduction: heat in solids (metals are conductors, wood/plastic are insulators)
- Convection: heat in liquids/gases by particle movement (sea breeze, land breeze)
- Radiation: heat without medium (Sun to Earth through vacuum)
- Dark clothes absorb heat; light clothes reflect heat
- Wool traps air (insulator), does not produce heat
Common Mistakes to Avoid
- Confusing heat with temperature
- Thinking metals are "cold" — they conduct heat away from hand quickly
- Thinking wool generates heat — it only traps body heat
- Believing radiation needs a medium
Scoring Tips
- Compare clinical and lab thermometer in a table
- Draw sea breeze and land breeze diagrams with arrows
- Give 2 examples each of conduction, convection, radiation