Class ~ 2
Thermometer
Liquid - in - glass thermometers:
These thermometers rely on the principle that liquids expand when heated.
They consist of a glass bulb containing a liquid (usually mercury or alcohol) and a narrow glass tube with a scale.
As the temperature increases, the liquid expands and rises up the tube, allowing for temperature measurement.
Mercury thermometers: are commonly used for laboratory purposes.
Alcohol thermometers: are used in clinical settings.
Bimetallic strips:
These strips are made of two different metals that expand at different rates when heated.
When heated, the strip bends, and this bending can be used to indicate temperature.
Thermocouple thermometers:
These thermometers use the principle that a temperature difference between two different metals produces a voltage.
The voltage produced is proportional to the temperature difference, allowing for temperature measurement.
When two different metals are joined together and one end of the junction is heated or cooled, a voltage is generated. This voltage is proportional to the temperature difference between the two ends of the junction.
Liquid in glass Thermometer ~ These are commonly used in laboratories and for general temperature measurement.
Thermocouples are used to measure temperature, especially when dealing with rapidly changing or very high temperatures, as they offer a fast response and a wide temperature range.
Bimetallic thermometers are used to measure temperatures between −75°C and +1500°C.
Specific Heat Capacity and Specific Latent Heat
Specific Heat Capacity:
Definition: Specific heat capacity (often denoted as 'c') is the amount of heat energy required to raise the temperature of 1 kilogram of a substance by 1 degree Celsius (or 1 Kelvin).
Purpose: It determines how much energy is needed to change the temperature of a substance without causing a phase change.
Units: Joules per kilogram per degree Celsius (J/kg°C) or Joules per kilogram per Kelvin (J/kg·K).
Example: Water has a high specific heat capacity, meaning it takes a lot of energy to heat up or cool down, which is why it's used in many cooling systems.
Equation: The heat (Q) required to change the temperature of a substance is calculated using: Q = m c ΔT, where:
Q = heat energy [J]
m = mass [kg]
c = specific heat capacity [J/kg·°C]
ΔT = change in temperature [°C]
Latent Heat:
Definition: Latent heat (often denoted as 'L') is the energy absorbed or released during a phase change (like melting, freezing, boiling, or condensation) at a constant temperature.
Purpose: It's the energy needed to break or form intermolecular bonds, causing a change in state without a change in temperature.
Types:
Latent heat of fusion: The energy required to change a substance from a solid to a liquid (melting) or from a liquid to a solid (freezing) at its melting point.
Latent heat of vaporization: The energy required to change a substance from a liquid to a gas (boiling or evaporation) or from a gas to a liquid (condensation) at its boiling point.
Units: Joules per kilogram (J/kg).
Example: When ice melts, it absorbs latent heat of fusion, and when water boils, it absorbs latent heat of vaporization, both at their respective phase change temperatures.
Equation: The heat (Q) required for a phase change is calculated using: Q = m * L, where:
Q = heat energy [J]
m = mass [kg]
L = specific latent heat [J/kg]
Waves
Longitudinal Waves: The particles of the medium vibrate in the same direction as the wave travels (e.g., sound waves).
Transverse Waves: The particles of the medium vibrate perpendicular to the direction the wave travels (e.g., electromagnetic waves).
How do digital thermometers measure temperature differently from liquid-in-glass thermometers?
Why do thermometers need to be calibrated, and how can incorrect calibration affect temperature readings?
What makes infrared thermometers ideal for measuring the temperature of distant or moving objects?
How do food thermometers ensure that food is cooked to safe and recommended temperatures?