difference in temperature, the greater the emf. This can be measured with a millivolt- meter. It is worth noting that thermocouples measure the temperature difference between two points, not absolute temperature. Thermocouples can be connected in series with each other to form a thermopile, where all the hot junctions are exposed to the higher temperature and all the cold junctions to a lower temperature.Thus, the voltages of the individual thermocouples add up, which allows for a larger voltage, making it easier to measure.
Weights Piston
Graduated glass syringe
Copper wire mV
Sensitive voltmeter
Fixed volume of gas
Rubber cap Iron wire
Test junction
Reference junction Fig 8.3: Thermocouple
Fig 8.4: Gas syringe being kept at constant volume by varying the pressure
Pressure of a gas at constant volume
When a fixed mass of gas is contained in a gas syringe sealed with a rubber cap, the pressure required to keep the volume constant varies with temperature. We can demonstrate the principle using the set-up as illustrated in Fig 8.4. When the gas is heated, more weight must be added to the top of the plunger (thus increasing the pressure) to keep the volume constant.The greater the rise in temperature, the more weight required.
Volume of a gas at constant pressure
When a fixed mass of gas is contained in a gas syringe sealed with a rubber cap and the pressure is kept constant, the volume increases with increasing temperature.We can demonstrate the principle using the set-up as illustrated in Fig 8.5.Atmospheric pressure acts on the plunger, causing the gas to be at constant pressure. If the temperature of the
