# Heat (1)

What is Heat And Temperature:

Heat is a form of energy that could alter the value of temperature. Heat refers to a quantity of energy transferred between two bodies. It is a measure of the total kinetic energy of the atoms or molecules in a body.

The units it is measured is in Joules (J) or kiloJoules (kJ). The heat content of a body will depend on its temperature, its mass, and the material it is made of.

Heat energy is always transferred from an object at high temperature to one at a lower temperature.

Temperature is not the same as heat, Temperature measures the degree of hotness of a body. It doesn’t depend on the mass or the material of an object. It can be thought of as a measure of the average kinetic energy of the atoms or molecules in a body.

As the temperature decreases, the kinetic energy of the particles will decrease. This means that as the temperature of a body decreases, heat energy of the body also decreases.

Thermal equilibrium is a state that two objects reach the same temperature by exchanging heat.

Zeroth law of thermodynamics: Zeroth law of thermodynamics states that If two objects are in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

NOTE: The “third body” in a practical situation is just the thermometer.

This means that if two separate systems or objects are each in thermal equilibrium with a third system or object, then all three systems are in thermal equilibrium with each other and thus have the same temperature.

The thermometer works on the principle of Zeroth law of thermodynamics. The thermometer is, in fact, measuring its own temperature. With Zeroth law, we know that the measured temperature is also the temperature of the object(In this case the human body) that has the thermal equilibrium with the thermometer. If system A and system B are each in thermal equilibrium with system C, then system A and B are in thermal equilibrium with each other.

TEMPERATURE SCALES

Temperature is measured using a variety of temperature scales. The most commonly used are:

The Celsius Scale (°C). This scale puts the freezing point of water at Oo C and the boiling point

of water at 100o C. The temperatures in between are divided up into 100 units (degrees).

The disadvantages of this scale are:

• There may be temperatures below Oo C.

The pressures and volumes of gases do not change in proportion to Celsius temperature.

2. The Kelvin Scale (K). This scale has absolute zero as the zero point on it’s scale. The size of the degree is the same as a Celsius degree.

• There are no negative temperatures.

• Pressures and volumes of gases will change in proportion to Kelvin temperature.

Absolute zero is 273 degrees below Oo C.

3. The Fahrenheit Scale(F). Fahrenheit is a thermodynamic temperature scale, where the freezing point of water is 32 degrees Fahrenheit (℉) and the boiling point 212℉ (at standard atmospheric pressure).

NOTE: There are many different types of thermometer used for measuring temperature e.g. mercury, alcohol, bi-metallic strip, thermocouple, electrical resistance, brightness thermometer etc.

CONVERTING TEMPERATURE SCALES.

Degree Celsius to Fahrenheit.

TF = 1.8 * ToC + 32

TF is the value in Fahrenheit and ToC is the value in Celsius.

b. Degree Celsius to Kelvin.

TK = ToC + 273.15

Examples.

Convert 100oC to kelvin.

Solution.

ToC = 100oC, TK = ?

Therefore, Tk = ToC + 273.15 becomes; TK = 100 + 273.15

Thus; TK = 373.15K

2. Convert 212oF to Celsius.

TF =212oF, ToC = ?

TF = 1.8 * ToC + 32

Substituting the given values into the equation,we have;

212 = 1.8 * ToC + 32

212 – 32 = 1.8 * ToC

180 = 1.8 * ToC

ToC = 1801.8

Therefore, ToC = 100oC

Note: To convert degree fahrenheit to Kelvin, first convert to Celsius, before converting to Kelvin using the formulae above.