Joule’s Law
According to Joule, whenever heat is converted into work or work is converted into heat, then the ratio of between work and heat in constant.
\(\frac{W}{Q}\) = J
where J is the mechanical equivalent of heat.
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Joule’s Law of Heating | Definition of Joule’s Law – Thermometry and Calorimetry
When water falls from height h, then increase in temperature dT at the bottom is
dT = \(\left(\frac{g h}{J \cdot C}\right)^{\circ} \mathrm{C}\)
- When m kg of ice-block falls from height h and its some part m’ is melt down, then
h = \(\frac{m^{\prime}}{m}\left(\frac{J L}{g}\right)\) meter
If ice-block melts completely, then m = m’ and hence h = \(\frac{J L}{g}\)
“Joule’s first law” (Joule heating), a physical law expressing the relationship between the heat generated and current flowing through a conductor.
“Joule’s second law” states that the internal energy of an ideal gas is independent of its volume and pressure, depending only on its temperature.
Melting
Conversion of solid into liquid state at constant temperature is called melting.
Fusion and Freezing Point
The process of change of state from liquid to solid is called fusion. The temperature at which liquid starts to freeze is known as the freezing point of the liquid.
Evaporation
Conversion of liquid into vapour at all temperatures (even below its boiling point) is called evaporation.
Boiling
When a liquid is heated gradually, at a particular temperature the saturated vapour pressure of the liquid becomes equal to the atmospheric pressure, now bubbles of vapour rise to the surface of the liquid. This process is called boiling of the liquid.
The temperature at which liquid boils is called boiling point.
The boiling point of water increases with increase in pressure and decreases with decrease in pressure.
Sublimation
The conversion of a solid into vapour state is called sublimation.
Hoar Frost
The conversion of vapours into solid state is called hoar frost.
Thermometry and Calorimetry:
The thermometer is a device used to check the temperature of an object. This branch of measurement of the temperature of a substance is called thermometry. It is measured in degrees or Fahrenheit, usually.
Calorimetry also means the measurement of heat but in joules. It states the amount of heat lost by the body is the amount of heat gained by its surrounding.