Thermal Equilibrium

Thermal Equilibrium

4.1

Thermal Equilibrium

When two objects come into contact, heat will be transferred
Net heat moves from hotter objects to cooler objects
The temperature of the cold object increases, the temperature of hot objects is reduced
When the temperature of the objects is the same, heat transfer is equal and net heat transfer is zero
Object has reached thermal equilibrium

Conditions for thermal equilibrium

Same temperature
Same rate of heat flow
Net heat flow zero

Mercury thermometer

The benefits of using mercury:

High boiling point
Low melting point
Good heat conductor
Expands and contracts uniformly
Opaque (easily visible)
Cohesive forces high (non-stick to wall)

How to increase the sensitivity of a mercury thermometer

Reduce the thickness of the glass bulb
- Heat transfer between the mercury and environment faster
Reduce the thickness of the glass bulb
- Absorbs heat from the environment with higher rates
Use small diameter capillary tubes
- Mercury rise higher when the diameter of the tube decreases
Reduce the thickness of the glass tube
- Heat transfer between the mercury and environment faster

Thermometer calibration

To calibrate a thermometer means to put the correct mark of reading at the correct place so that other temperature can be deduced from these marks.
To do this, two extreme points are chosen to mark its scale and these points must be able to be reproduced accurately.
Usually, we take the steam point of pure water as \(100\;^0\text{C}\) and the ice point of water as \(0\;^0\text{C}\).

	Calculation for non-calibrated thermometer
	\(\theta=\dfrac{l_\theta-l_0}{l_{100}-l_0}\times100\;^0\text{C}\), where \(\theta\) = temperature, \(l_0\) = length when temperature is \(0\;^0\text{C}\), \(l_{100}\) = length when temperature \(100\;^0\text{C}\)