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29th Oct 2019 @ 4 min read
Boyle's law is a famous gas law studied in physics and chemistry. It relates pressure and volume of gas keeping other parameters (amount of gas and temperature) constant. There are several ways to verify the law. The article covers a standard laboratory method to verify the law by studying the relation between pressure and volume.
To verify Boyle's law i.e. for a given amount of gas, absolute pressure is inversely proportional to volume at a constant temperature.
Air column with measuring scale, Bourdon pressure gauge, oil reservoir, hand air pump, barometer
The air column is connected to the oil reservoir such that the air in the column is completely sealed off by the oil.
A sample observation table is provided below.
|Pressure reading (kPa)||Volume reading (cm3 or ml)|
Pressure and volume are the two parameters are measured throughout the experiment. The experiment is performed at a constant temperature which is room temperature. The amount of the gas in the column is also constant. Thus, the conditions of Boyle's law are satisfied.
The volume readings are in cm3 and the pressure readings are in kPa. The pressure measured is gauge pressure, not absolute. So, we need to add the atmospheric pressure to the readings to obtain absolute pressure. The atmospheric pressure is obtained from a barometer, but it is considered as 1 atm i.e. 101.325 kPa.
For example, a gauge pressure of 650 kPa is an absolute pressure of 650 + 101.325 = 751.325 kPa. The table below lists absolute pressure.
|Pressure reading (kPa)||Absolute pressure (kPa)|
The final table consists of absolute pressure (kPa), volume (cm3), inverse volume (cm−3), and pressure-volume (kPa cm3).
|Absolute pressure (kPa)||Volume (cm3)||Inverse volume† (cm−3)||Pressure-volume† (kPa cm−3)|
|Note: † rounded off to two significant figures.|
As observed from the table above, pressure-volume nearly remains constant i.e. PV = k.
The graph of pressure vs volume and pressure vs inverse volume are plotted.
As expected, the above graph (pressure vs volume) is an exponential curve. As observed from the graph, pressure decreases with rise in volume or vice versa.
The graph of pressure to inverse volume is a straight line and follows the equation y = mx.
The experiment is successfully studied, and the system obeys Boyle's law. From the graphs, it can be concluded that the pressure of the gas in the column is inversely proportional to the volume of the gas at a constant temperature for a fixed amount of gas.
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