Chapter-4: Heat and Temperature 7th Notes CBSE
Heat and Temperature
➥ Heat and temperature are essential concepts in understanding how energy is transferred between objects and how we measure this energy.
Heat
➥ Heat is a form of energy that flows from a hotter object to a cooler object.
➥ It is measured in Joules (J).
Units of Temperature
➥ Temperature is commonly measured in degrees Celsius (°C), Fahrenheit (°F), or Kelvin (K).
Measuring Temperature
➥ Temperature can be measured using various instruments like thermometers. These devices help provide accurate readings of the heat level in objects or the environment.
1. Clinical Thermometer
➥ A clinical thermometer is used to measure human body temperature. It has a range from 35°C to 42°C.
Reading the Thermometer
➥ To read a thermometer, ensure it is at eye level and the mercury level is stable before taking the reading.
2. Laboratory Thermometer
➥ A laboratory thermometer is used in experiments to measure temperatures ranging from -10°C to 110°C.
Differences Between Clinical and Laboratory Thermometers
| Feature | Clinical Thermometer | Laboratory Thermometer |
|---|---|---|
| Purpose | Measures body temperature | Measures temperature in experiments |
| Range | 35°C to 42°C | -10°C to 110°C or more |
| Scale | Fahrenheit or Celsius | Celsius |
| Material | Glass with mercury or alcohol | Glass with mercury or alcohol |
| Design | Narrow and long | Thicker and shorter |
Transfer of Heat
➥ Heat can transfer from one object to another through conduction, convection, or radiation.
Conduction
➥ Conduction is the transfer of heat through direct contact, occurring mainly in solids like metals.
Convection
➥ Convection involves the transfer of heat through fluids (liquids or gases), where warmer areas move upward and cooler areas move downward.
How Heat Moves Through Air
➥ Heat in air is primarily transferred through convection. Warm air rises, and cool air sinks, creating a circular movement.
Sea Breeze and Land Breeze
➥ During the day, cooler air from the sea moves towards the land, creating a sea breeze. At night, the reverse happens, leading to a land breeze.
Radiation
➥ Radiation is the transfer of heat through electromagnetic waves, requiring no medium. The Sun heats the Earth through radiation.
Kinds of Clothes We Wear in Summer and Winter
➥ In summer, we wear light-colored, loose clothes to stay cool, while in winter, we wear dark, thick clothes to retain heat.
Thermos Flask
➥ A thermos flask is designed to minimize heat transfer, keeping liquids hot or cold for extended periods by using vacuum insulation.
Hot and Cold Objects
➥ Objects that feel hot or cold to the touch give us a basic sense of temperature. This feeling, however, can be subjective and influenced by surroundings.
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