用毛细管升高法测液体的表面张力系数.ppt

用毛细管升高法测液体的表面张力系数 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望 Aim nTo determine the surface tension value of water against air by the method of capillary rise.nTo learn the use of reading microscope.This unequal attraction causes the water at the air-water interface to act as a cohesive surface and the liquid to shrink to the smallest possible surface area.A water molecule deep within the liquid experience forces of attraction by all its neighbors net force=zeroA water molecule at the surface lacks neighboring water molecules toward the interface net force is not zero(directed downwards)Introduction defined as:Surface tension -Scientificaly where is the surface tension of the liquid.As defined here the dimensions of surface tension are force per length,and its units are .The force along a line of unit length,where the force is parallel to the surface but perpendicular to the line,tending to minish the area of the surface Theory Surface tension produces several phenomena.The rise of a liquid in a capillary is the result of surface tension.Consider the simple situation in Fig.1,in which the end of a capillary tube is immersed in a liquid,one observes a substantial rise of liquid in the capillary due to surface tension.The balance point can be used as a means to measure the surface tension:where d is the diameter of the capillary,h is the capillary rise,is the liquid density,g is the acceleration due to gravity.Thus,after determine the value of h and d in this experiment,the surface tension of water can be calculated.Fig.12rhApparatus nReading microscope nBeakernCapillarynThermometernLight source nSupport of capillary Reading microscope EyepieceObjective lensFocus handwheelMicrometrical drumReading scaleReading dial Fig.2For example,reading is 29.723mm in Fig.3.（Note:The recorded data should include the last estimated figure.）1main scale2reading line of main scale 3micrometrical drum4reading line of micrometrical drum Fig.3Procedure 1 Illuminate the object by light source,adjust the direction of light and make the field of view be bright.2 Adjust eyepiece until the cross-hair is clear.3 Get rid of the water in capillary.Put capillary into the hole of support and make the end of capillary dip into the beaker filled with water.Raise and lower the capillary several times until it is wetted.When the water wets the walls of the capillary,the water is“pulled”up by the surface tension force.Pull capillary upward from lower slowly until its liquid level achieves the highest.Procedure 4 Put the beaker on object stage，find the clear image of liquid levels of capillary and beaker separately by adjusting the distance from lens to object.Procedure hh5 Use the reading microscope to determine the capillary rise of water.timesProcedure Fill the table with experiment data：hmm6 Take out the capillary and get rid of water in it.Put the capillary on the support and making the end of it toward objective lens.Adjust the reading microscope until find the ring image of capillary and the color of the ring is green(as below).Procedure dd7 Determine the internal diameter of the capillary.Procedure Fill the table with experiment data：8 Record the temperature t of the water.mmData processing nCalculate the surface tension of water.nCompare the result with the standard value and calculate the relative error.