Learning Objectives
- Understand hot and cold objects and temperature
- Learn how to use a thermometer
- Know about transfer of heat
- Understand types of clothing for different seasons
Key Concepts
Temperature and Thermometer
Temperature: The degree of hotness or coldness of a body. Measured using a thermometer.
Clinical thermometer: Range 35°C to 42°C. Used to measure body temperature. Has a kink to prevent mercury from flowing back.
Laboratory thermometer: Range -10°C to 110°C. Used for scientific experiments. Must be kept upright.
Normal human body temperature: 37°C (98.6°F)
Transfer of Heat
Conduction: Transfer of heat through a solid material from hot end to cold end without the material moving. Metals are good conductors; wood, plastic are poor conductors (insulators).
Convection: Transfer of heat in liquids and gases by actual movement of the medium. Hot air/water rises, cool air/water sinks, creating convection currents.
Radiation: Transfer of heat without any medium. Heat from the sun reaches earth through radiation. Dark-coloured objects absorb more heat; light-coloured objects reflect more heat.
Conductors and Insulators
Conductors: Materials that allow heat to pass through them easily (metals like iron, copper, aluminium).
Insulators: Materials that do not allow heat to pass through easily (wood, plastic, wool, air).
Clothing
We wear light-coloured cotton clothes in summer (absorb less heat, allow air circulation). We wear dark-coloured woollen clothes in winter (trap air which is a poor conductor, absorb more heat from surroundings).
Summary
Temperature measures hotness or coldness. Heat transfers by conduction (solids), convection (fluids), and radiation (no medium needed). Conductors allow heat flow; insulators resist it. Woollen clothes keep us warm by trapping air, which is a poor conductor of heat.
Important Terms
- Conduction: Heat transfer through solids
- Convection: Heat transfer through fluids by movement
- Radiation: Heat transfer without medium
- Conductor: Material that allows heat transfer
- Insulator: Material that resists heat transfer
Quick Revision
- Clinical thermometer: 35°C–42°C, Lab thermometer: -10°C–110°C
- Normal body temperature: 37°C
- Conduction in solids, Convection in fluids, Radiation needs no medium
- Dark colours absorb heat, Light colours reflect heat
- Wool traps air (insulator) → keeps warm