# Boyle's Law Experiment for Class 11

Boyle's Law Experiment for Class 11

BOYLE’S LAW I (Using Boyle's Law)

Aim:

To verify Boyle's law using Boyle's Law apparatus and to determine the atmospheric pressure.

Apparatus:

Boyle's law apparatus consists of a uniform glass tube AB closed at one end. The open end is connected to a reservoir R, by means of a rubber tube. The reservoir contains mercury. The glass tube contains pure dry air. The glass tube and the reservoir are fitted to a vertical graduated board. The reservoir can be raised or lowered and can be fixed at any position. A scale is fixed between AB and R.

Principle:

According to Boyle's law, at constant temperature, the pressure of a given mass of gas is inversely proportional to its volume.

ie., P x V =a constant.

Since the volume of air in the glass tube is directly proportional to the length 'l'.

P x l = constant

Procedure

a. To verify Boyle's law

i. The atmospheric pressure H is noted from a Fortin's barometer.

ii. The reservoir is adjusted till the mercury levels in the AB and the reservoir are the same. Now, the pressure of air inside AR is equal to the atmospheric pressure (H). The reading of the closed end of the glass tube AB is noted as R1. The length of air column (l) is measured.

iii. The reservoir is raised and fixed at a particular height. (Mercury level in R is above than that in AB). The difference in levels of mercury in the reservoir and in the closed tube AB is noted as h. The pressure P of air inside the tube in H + h.

iv. The reservoir is lowered and fixed at a particular height. (Mercury level in R is below than that in AB). The difference in levels of mercury in the reservoir and the closed tube is noted as h. The length of the air column l is measured. The pressure P of air inside the tube is H — h. Repeat the experiment with mercury level in the reservoir above that in the tube AB and also with mercury level in the reservoir below that in the tube AB. Do experiment three times in each case.

In each case P x l = constant, verifies Boyle's law. A graph between P and 1/l is found to be a straight line.

b. To determine the atmospheric pressure.

Applying Boyle's law

P x l = constant

i.e., (H ± h1) l1 = (H ± h2)l2

(H + h1)l1 = (H + h2)l2

H = (h2l2-h1l1)/(l1-l2)

where h1 and h2 are the difference in mercury levels in the two limbs in any two cases and l1 and l2, are the corresponding lengths of the air column. (If the mercury level in the reservoir is below that in the glass tube AB, then height is taken as negative and vice versa.)

A graph is drawn with h along the X - axis and 1/l along the Y- axis. The X intercept (negative side of the X - axis) gives the atmospheric pressure (H). (The sign of h must he considered in drawing the graph)

Plot, P-1/l graph

i. To verify Boyle’s law

Atmospheric pressure, H = …….. cm of Hg

Reading of the closed end A of the tube = R1 = …….. cm

ii. To determine the atmospheric pressure

Mean H = ……..cm of Hg = ……..m of Hg

Plot h-1/l graph

Atmospheric pressure, H(OB) = ……… cm of Hg = ………m of Hg

Results:

i. P x l = constant, verifies Boyle's law

ii. Atmospheric pressure,

a. By calculation =.......... m of Hg

b. From graph = ………. m of Hg

BOYLE’S LAW II (Using Quill Tube)

Aim: To study the variation in volume with pressure of a given mass of gas at constant temperature.

Apparatus: Quill Tube, Stand, Meter scale etc.

A quill tube is a uniform tube closed at one end. By means of a pellet of mercury, a certain mass of air is enclosed in the tube.

Principle:

According to Boyle's law, at constant temperature, the pressure of a given mass of gas is inversely proportional to its volume.

ie, P x V = a constant.

Since the volume of air in the quill tube is directly proportional to the length ‘l'

P x l = constant

Procedure

(a) Horizontal Position

The quill tube is held horizontally. The length of air column is measured. Vertical height at the two ends of mercury thread from the table are measured. The difference between them gives vertical height `h' of the mercury thread, Here h = 0. Pressure inside the tube = H

(b) Vertical Position (Closed end downwards)

The quill tube is then held vertically by means of a stand with closed end downwards. Length of air column (l) is measured. Vertical height h of Hg is noted. The pressure inside the tube = H + h.

(c) Slanting Position (Closed end downwards)

The quill tube is then placed in a slanting position with the closed end downwards, Then length of air column (l) is measured. Vertical height h of Hg is noted. The pressure inside the tube = H + h.

(d) Vertical Position (Closed end upwards)

The quill tube is now held vertically with the closed end up. The length of air column (l) is measured. The vertical height 'h' of Hg is noted. The pressure inside the tube = H-h.

(e) Slanting Position (Closed end upwards)

The quill tube is then placed in a slanting position with the closed end up. The length of air column and vertical height ‘h’ of Hg is noted. The pressure inside the tube = H-h.

In each case P x l = constant, verifies Boyle’s law. A graph between h and 1/l is found to be a straight line.

Atmospheric pressure H = 76 cm of Hg

Plot P-1/l graph

Result:

P x l = constant, verifies Boyle’s law.

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