Measurement of surface tension coefficient of liquid

【Experimental Name】Measurement of surface tension coefficient of liquid

【Objective of experiment】

1. Master the method of calibrating silicon pressure resistance sensor with weights.

2. The physical process and phenomenon of measuring surface tension of pure water by

pulling method were observed.

【Principle of experiment】

At the boundary between a liquid and a gas, at the surface of the liquid and the

interface between two liquids that do not mix, there is an extremely small pull due to

the attraction between the molecules. The reason for this is that there is a thin layer

on the surface where the liquid and gas contact, called the surface layer. The

molecules in the surface layer are sparser than those in the liquid interior, and the

distance between the molecules is larger than that in the liquid interior. The

interaction between the molecules is manifested as gravity. Imagine that there is a

thin film on the surface. It is subjected to the tensile force of the surface. This tension

of the liquid is called the surface tension. In our daily life, the water droplets hanging

on the branches after rain, the water is slightly above the mouth of the cup without

spilling, and other phenomena are the result of surface tension.

The equilibrium equation of the force before and after the lifting plate is separated from

the liquid surface is:

【 Experimental apparatus 】

1. FD-NST liquid surface tension coefficient tester

(1) Lifting adjustment nut: rotate it to make glassware. Up or down. (2) Liquid dish: place

the liquid to be tested.

(3) Force sensor: the tension of the metal ring on the sensor is measured during the

experiment. (4) Host: display voltage signal of force sensor.

2. Instrument composition and technical indicators

(1) Measuring range: 0-0.098N

(2) Sensitivity: about 3.00VN

(3) Nonlinear error: <0.2%+

(4) Supply voltage: DC 5-12V

【Content of Experiment】

1. Calibration of force sensor

There are individual differences in the sensitivity of the force sensor, so calibration should

be performed before the experiment. The steps are as follows:

(1) Turn on the power switch and preheat the instrument for 5-10 minutes.

(2) Hang the weight tray under the small hook of the sensor beam.

(3) Add weights of 0.5g, 1.0g, 1.5g, 2.0g, 2.5g and 3.0g on the weight tray respectively,

and record the reading value U of the corresponding digital voltmeter.

2. Ring measurement and cleaning

(1) Measure the outer diameter D1 and inner diameter D2 of the metal ring with a vernier

caliper.

(2) Before the experiment, clean the metal ring hanging plate with water.

3. Measure the surface tension coefficient of the liquid

(1) Hang the metal ring lifting plate on the small hook of the sensor, adjust the lifting

platform, raise the liquid near the lower edge of the ring plate, and observe whether the

lower edge of the ring lifting plate is parallel to the liquid level to be measured. If it is not

parallel, it is necessary to remove the metal ring hanging plate and adjust the filaments

on the hanging plate so that the hanging plate is parallel to the liquid level to be

measured. Sometimes it must be repeatedly operated.

(2) Adjust the lifting nut to make the liquid dish rise gradually, immerse the lower part of

the ring piece in about 1mm below the liquid level to be measured, and then reverse

adjust the lifting nut to make the liquid level gradually fall. An annular liquid film will be

formed between the metal ring sheet and the liquid surface, and the liquid level will

continue to descend. The digital voltmeter reading U1 and U2 will be measured before

and after the moment of the annular liquid film breaking.

(3) Repeat the operation in (2) six times.

【Precautions】

1. The level of the ring must be adjusted well.

2. When rotating the lifting nut, the vibration of the liquid dish should be reduced as

far as possible. Meanwhile, the interference of the liquid film caused by breathing,

sound wave and the movement of surrounding students should be minimized.

3. The body part shall not touch the test platform, and the lifting nut shall be

operated with both hands in the air.

【 Data recording form】