Hot and Cold

Key Notes :

Definition of Temperature:

  • Temperature is a measure of how hot or cold an object is. It indicates the level of heat energy present in an object.
  • It is measured in units like Celsius (°C), Fahrenheit (°F), and Kelvin (K).

Hot vs. Cold:

  • Hot objects have a higher temperature, while cold objects have a lower temperature.
  • Our sense of touch can be misleading; we need thermometers for accurate temperature measurement.

Thermometers:

  • Devices used to measure temperature.
  • Clinical thermometers are used for measuring human body temperature.
  • Laboratory thermometers measure a wider range of temperatures, useful in scientific experiments.
  • Digital thermometers have replaced mercury-based ones due to safety concerns.

Heat and Its Transfer:

  • Heat is a form of energy that flows from a hotter object to a colder object.
  • Conduction, convection, and radiation are the three modes of heat transfer.
    • Conduction: Heat transfer through direct contact (e.g., metal spoon in hot soup).
    • Convection: Heat transfer through fluids (liquids and gases) due to movement (e.g., boiling water).
    • Radiation: Heat transfer through electromagnetic waves (e.g., warmth from the sun).

Effects of Heat:

  • Expansion: Objects expand when heated and contract when cooled.
  • Change in State: Heat can cause substances to change states, like melting (solid to liquid), evaporation (liquid to gas), and condensation (gas to liquid).
  • Thermal Energy: The total kinetic energy of all particles in a substance.

Temperature Scales:

  • Celsius (°C): Water freezes at 0°C and boils at 100°C.
  • Fahrenheit (°F): Water freezes at 32°F and boils at 212°F.
  • Kelvin (K): Absolute zero (0 K) is the lowest possible temperature, where all molecular motion stops. Water freezes at 273 K and boils at 373 K.

Heat vs. Temperature:

  • Heat is the total energy of molecular motion in a substance, while temperature is the measure of the average energy of molecular motion.
  • Heat is measured in joules (J), whereas temperature is measured in degrees.

Everyday Examples:

  • A hot cup of tea cools down over time as it loses heat to the surroundings.
  • Ice melts when left out in the open due to heat absorption.

Let’s practice!