Heat - Heat and Temperature

Heat is a form of energy that flows from a body at a higher temperature to a body at a lower temperature. Its SI unit is the Joule ($J$), and another common unit is the calorie ($cal$), where $1 \text{ cal} \approx 4.186 \text{ J}$.

Temperature is the measure of the degree of hotness or coldness of a body. The SI unit of temperature is Kelvin ($K$), though Celsius ($^\circ C$) and Fahrenheit ($^\circ F$) are commonly used in daily life.

The Celsius scale has a lower fixed point (melting point of ice) at $0^\circ C$ and an upper fixed point (boiling point of water) at $100^\circ C$.

The Fahrenheit scale has a lower fixed point at $32^\circ F$ and an upper fixed point at $212^\circ F$.

The Kelvin scale is the absolute scale of temperature. The relationship between Kelvin and Celsius is $K = C + 273$. Absolute zero is $0 \text{ K}$ or $-273^\circ C$.

Thermal expansion is the increase in the size of an object when heated. Different materials expand by different amounts for the same rise in temperature.

A Clinical Thermometer is used to measure human body temperature, ranging from $35^\circ C$ to $42^\circ C$. It has a 'kink' to prevent the backflow of mercury.

Specific Heat Capacity is the amount of heat energy required to raise the temperature of a unit mass of a substance by $1^\circ C$. It is denoted as $s$ or $c$.