travelling microscope experiment capillary tube

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• To Find The Surface Tension Of Water By Capillary Rise Method

To Determine the Surface Tension of Water by Capillary Rise Method

Surface tension is the tendency of a liquid surface to shrink into the minimum surface area possible. The capillary rise method is one of the techniques to determine the surface tension of a liquid such as water. While experimenting with a capillary tube, it is observed that when a liquid rises in the tube, the weight of the liquid column is supported by the upward force of surface tension acting along the circumference of the points of contact. Let us learn about the experiment and the observations in detail.

To find the surface tension of water by capillary rise method.

Apparatus/ Materials Required

• Three capillary tubes of different radii
• A tipped pointer clamped in a metallic plate with a handle
• Travelling microscope
• Adjustable height stand
• A flat bottom open dish
• Thermometer
• Clean water in a beaker
• Clamp and a stand

The surface tension of water is given by the formula

where, r is the radius of cross-section, g is the acceleration due to gravity, ρ is the density of the liquid, h is the capillary rise, θ is the contact angle.

(a) Arranging the apparatus

• Place the adjustable height stand on the table and make its base horizontal by levelling the screws.
• Take dirt and grease-free water in an open dish with a flat bottom and put it on top of the stand.
• Take three capillary tubes of different radii.
• Clean the tubes and dry them and then clamp them to a metallic plate to increase the radius. Clamp a pointer after the third capillary tube.
• Clamp the horizontal handle of the metallic plate in a vertical stand so that the capillary tube and the pointer become vertical.
• Adjust the height of the metallic plate that the capillary tubes dip in the water in the open dish.
• Adjust the position of the pointer such that the tip touches the water surface.

(b) Measurement of capillary rise

• Calculate the least count of the travelling microscope for vertical and horizontal scales.
• Raise the microscope to a suitable height pointed towards the capillary tube with a horizontal axis.
• Focus the microscope on the first capillary tube.
• Make the horizontal crosswire touch the central part of the concave meniscus seen convex through the microscope
• Note the reading of the microscope on the vertical scale.
• Move the microscope horizontally and bring it in front of the second capillary tube.
• Lower the microscope and repeat steps 4 and 5
• Likewise, repeat steps 4 and 4 for the third capillary tube
• Lower the stand for the pointer tip to be visible.
• Move the microscope horizontally and bring it in front of the pointer.
• Lower the microscope and make the horizontal crosswire touch the tip of the pointer.

(c) Measurement of the internal diameter of the capillary tube

• Place the first capillary tube horizontally on the adjustable stand.
• Focus the microscope on the end dipped in water. A white circle with a green strip will be visible.
• Make the horizontal cross-wire touch the inner circle at point A.

Observation

The least count of the travelling microscope (L.C) = ….. cm.

Height of liquid rise

The internal diameter of the capillary

Calculation

Put the value h and r for each capillary tube separately and find the values of T using the following formula:

Find the mean value of the obtained T values as follows:

The surface tension of water at t °C is _____ dynes cm –1 .

1. Explain the relationship between surface tension and surface energy.

Answer: The relationship between surface tension and surface energy is given as follows:

Surface Energy = Surface tension × Change in area

2. Which side of the liquid surface has more pressure?

Answer: The pressure is more on the concave side of the free liquid surface.

3. What is capillary?

Answer : An open-ended tube with a fine bore is known as capillary.

4. Why should the liquid be free from grease?

Answer: Grease reduces the surface tension of the liquid.

5. What is the surface tension of water?

Answer: The surface tension of water is 7.275 × 10 –2 N-m –1 at 20 °C.

6. Why do you measure the internal diameter of the capillary tube in two mutually perpendicular directions?

Answer: It is done to take the mean to eliminate the error if the bore is not circular.

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How to measure the inner diameter of thin tube (0.5mm to 2mm)

Does anybody know what method or equipment could be used to measure the inner diameter of capillary tubes? They would be in the region of 0.5-2mm in diameter.

Edit: the tube is made of plastic and I have standard lab equipment available.

• experimental-physics
• measurements
• home-experiment

• $\begingroup$ If you are talking about metal capillary tubes, take a look at this article nvlpubs.nist.gov/nistpubs/jres/045/jresv45n4p283_A1b.pdf $\endgroup$ –  J. Shupperd Commented Aug 27, 2016 at 15:44
• $\begingroup$ I have an idea, but for it to be a good one I need to know a few things: 1) What is the tube made of? 2) Would it be ok to get the tube wet? 3) How much length of tube do you have available? $\endgroup$ –  DanielSank Commented Aug 27, 2016 at 20:26
• $\begingroup$ It would be helpful if you could tell us what material the tubes are made of, what length of tube you have available, and what other equipment you have. Micrometer, balance, accurate scale, microscope, ... What do you have? Is the tube transparent or not? Can you assume constant diameter? Do you know the material properties? Can your experiment destroy the tube? $\endgroup$ –  Floris Commented Aug 28, 2016 at 12:38

4 Answers 4

The simplest method is probably to use a travelling microscope to measure the wall thickness at the ends of the tube, and vernier calliper or micrometer to measure outer diameter at a few points along the tube. The drawback is that this does not give an average value for wall thickness.

This article entitled "The Exact Measurement of Capillary Holes" describes a method using hydraulic resistance applying Poiseuille's Formula. The apparatus is a little complicated but fairly basic, and could probably be further simplified. It claims an accuracy of at least an order of magnitude better than the microscope method.

(Item #3 on page 1 of a Google Search "measure diameter capillary tube". The article cited in J Shupperd's answer was #1 in the same search. Hence my down-vote for lack of research effort.)

• $\begingroup$ That fourth-power of $r$ thing sure help, doesn't it? $\endgroup$ –  dmckee --- ex-moderator kitten Commented Aug 27, 2016 at 23:58
• $\begingroup$ @dmckee : I didn't think about that when I posted this answer. It sounds like a good reason. $\endgroup$ –  sammy gerbil Commented Aug 28, 2016 at 1:30

An easily applied lab technique would be to measure a length of tubing, and find its outer diameter with a micrometer, then weigh it. Knowing the density of stainless steel or glass (or whatever) completes the equation.

mass = density * length * (D_outer **2 - D_inner **2)* pi/4

• $\begingroup$ This depends very much on knowing the exact density of the plastic used. $\endgroup$ –  sammy gerbil Commented Aug 28, 2016 at 21:37
• $\begingroup$ Yeah, even using a micrometer on a (possibly soft) plastic would make for some error bars. On the other hand, plastic parts aren't usually precise; I'd wonder, too, if the inner diameter is different when wet. $\endgroup$ –  Whit3rd Commented Aug 29, 2016 at 4:04

I'm not a physicist so what I'm saying may be senseless. Since you used the tag home-experiment I thought of something you could do at home. What if you fill with a syringe containing water the tube until it's full? By knowing how long the tube is and how much water the syringe had initially you could calculate the diameter (I think at least). To block the possible backdraught you could pierce first a pencil eraser(the built-in to the pencil). And yes, you can find syringe needle smaller than 0.5mm.

Some reasonable methods have already been proposed, but you might just measure the height of water column in the capillary (at least if the capillary is transparent) and calculate the diameter ( https://en.wikipedia.org/wiki/Capillary_action#Height_of_a_meniscus )

• $\begingroup$ As long as you know the contact angle - which requires you to know the properties of the water and the surface VERY well. Also it is not stated whether these capillaries are transparent. $\endgroup$ –  Floris Commented Aug 28, 2016 at 12:36
• $\begingroup$ @Floris: I agree with your comment. I would like just to note that I edited the answer to add the caveat on transparency (before you commented:-)) and that one can estimate the contact angle if the capillary is indeed transparent. $\endgroup$ –  akhmeteli Commented Aug 28, 2016 at 12:48

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Surface tension of water by the capillary tube method

Content of this page :.

1.     Introduction  of the experiment.

2.     Aim  of the experiment.

3.     Tools  of the experiment.

4.   Steps  and  methods  of the experiment.

5.     Parameter, Theory and Final law  of the experiment.

6.     Table  of The Readings.

7.     Medical application and advantages  of the experiment.

1. Introduction of the experiment:

Surface Tension  is a property of a liquid surface displayed by its acting as if it were a stretched elastic membrane. This phenomenon can be observed in the nearly spherical shape of small drops of liquids and of soap bubbles. Because of this property, certain insects can stand on the surface of water. The high surface tension of water is caused by strong molecular interactions. The surface tension arises due to cohesive interactions between the molecules in the liquid. At the bulk of the liquid, the molecules have neighboring molecules on each side.

2. Aim of the experiment:

-To measure  the surface tension  of water by capillary tube method.

·        Set of three glass capillary tubes-one of mm diameter. One of greater and one of less diameter.

·        Dilute nitric acid.

·        Dilute caustic soda solution.

·        Travelling microscope or glass scale.

·        Rubber bands.

·        Beaker.

·        Stand and clamp.

·        Thermometer.

4. Steps and methods of the experiment:

lean all three capillary tubes free from dirt and grease both inside and outside by washing them successively with nitric acid, with tap-water, with caustic soda solution and lastly and repeatedly with tap- water. The beaker and the glass scale (if used) must also be free from dirt and grease so clean them in the same way.

Select the capillary tube of medium bore and attach a bent pin to it by means of a rubber band. Hold the capillary tube in a clamp with its lower end immersed in the water. Before measuring the capillary rise push the tube a little farther down into the water and then restore it to its original position. This ensures that the tube is wet a little above the meniscus.

Adjust the position of the bent pin until its point just touches the water surface. Focus the microscope on the meniscus of the water level in the capillary tube and adjust the microscope until the horizontal cross- wire is tangential to the bottom of the meniscus which is of course seen inverted in the eyepiece of the microscope. To facilitate preliminary focusing of the microscope on the meniscus it is useful to hold a piece of paper with printing on it behind the capillary tube and first focus on that. Record the position of the travelling microscope on its vertical scale (h1).

Mark the position of the meniscus on the capillary tube with a loop of cotton or by gummed paper and then carefully remove the beaker of water from contact with the bent pin. Lower the microscope until it can now be focused on the tip of the bent pin. Record the position of the travelling microscope on its vertical scale (h2).

With the aid of a file cut the capillary tube at the place previously occupied by the meniscus and measure the internal diameter d by the travelling microscope, taking the mean of two determinations at right angles. Repeat all the measurements with the other two clean capillary tubes in turn.

Record the temperate of the water.

5- Parameters ,   Final Law  of The experiment

Parameters:

𝑦 : Surface tension in  ( 𝑁𝑚 −1)

𝑑 : Diameter of the capillary tube in  ( 𝑚 )

ℎ : Height of the water inside capillary tube in   ( 𝑚 )

𝜌 : Density of water  (1000kg 𝑚 −3)

𝑔 : Gravitational acceleration  (9.8 𝑚𝑠 −3)

Surface Tension  𝒚  = 𝟏 / 𝟒 𝒅𝒉𝝆𝒈

6. Table  of the Readings:

7 - Medical  Application:

In medicine, surface tension measurement is above all used in connection with various pathological states of lung surfactants such as  adult respiratory distress syndrome ,  bronchial asthma ,   and  pneumonia .

Download The Data Sheet

Terms and Conditions

Experiment of Surface Tension of Water by Capillary Rise Method

A clean capillary tube of uniform bore is fixed vertically with its lower end dipping into water taken in a beaker. A needle N is also fixed with the capillary tube as shown in the Figure. The tube is raised or lowered until the tip of the needle just touches the water surface.

A travelling microscope M is focused on the meniscus of the water in the capillary tube. The reading R 1 corresponding to the lower meniscus is noted. The microscope is lowered and focused on the tip of the needle and the corresponding reading is taken as R 2 . The difference between R 1 and R 2 gives the capillary rise h.

The radius of the capillary tube is determined using the travelling microscope. If ρ is the density of water then the surface tension of water is given by T = hrρg /2 where g is the acceleration due to gravity.

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Sunday 26 june 2016, experiment 09: surface tension of water by capillary tube method.

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SP015 Lab Manual 2020 EXPERIMENT 1 ___________________________________________________________________________ Title: MEASUREMENT AND UNCERTAINTY Objective: (a) To measure length of various objects. (b) To determine the uncertainty of length of various objects. Theory: Measuring some physical quantities is part and parcel of any physics experiment. It is important to realise that not all measured values are exactly the same as the actual values. This could be due to errors that we made during the measurement, or perhaps the apparatus that we used may not be accurate or sensitive enough. Therefore, as a rule, the uncertainty of a measurement must be taken and it has to be recorded together with the measured value. The uncertainty of a measurement depends on the type of measurement and how it is done. For a quantity x with the uncertainty x, its measurement is recorded as below: x  x The relative uncertainty of the measurement is defined as: x x and therefore its percentage of uncertainty is x 100% . x 1.1 Single Reading (a) If the reading is taken from a single point or at the end of the scale, x = 1  (smallest division from the scale) 2 (b) If the readings are taken from two points on the scale, x = 2  1  (smallest division from the scale)   2  (c) If the apparatus uses a vernier scale, ∆x = 1  (smallest unit from the vernier scale) 1 SP015 Lab Manual 2020 1.2 Repeated Readings For a set of n repeated measurements of x, the best value is the average value given by n 1.1  xi x  i1 n where n = the number of measurements taken xi = the ith measurement The uncertainty is given by n 1.2  x  xi x  i 1 n The result should be written as x  x  x 1.3 Apparatus: A metre rule A vernier callipers A micrometer screw gauge A travelling microscope A coin A glass rod A ball bearing A capillary tube (1 cm long) Procedure: 1. Choose the appropriate instrument for measurement of (i) length of a laboratory manual. (ii) diameter of a coin. (iii) external diameter of a glass rod. (iv) diameter of a ball bearing. 2 SP015 Lab Manual 2020 2. For task (i) to (iv), perform the measurement and record your results in a suitable table for at least 5 readings. Refer to Table 1.1 as an example. Determine the percentage of uncertainty for each set of readings. Table 1.1 No. Length of the laboratory manual, |    i | (..........)  ( .............) 1 2 n n 3 |  i | 4  i   i1 5  ........   i1  ............ Average n n 3. Use travelling microscope to measure the internal diameter of the capillary tube. Adjust the microscope so that the cross-hairs coincide with the left and right edge of the internal diameter of the tube as shown in Figure 1.1. Record dleft and dright. dleft dright The internal diameter, d  | dright  dleft | Figure 1.1 Determine the uncertainty and the percentage of uncertainty of the internal diameter of the capillary tube. 3

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Physics practicals class xi, objective of the experiment :, to determine the surface tension of a liquid by capillary rise method..

How do you define surface tension?

Surface tension is the property of a liquid, by virtue of which its free surface at rest behaves like an elastic skin or a stretched rubber membrane, with a tendency to contract so as to occupy minimum surface area. This property is caused by cohesion of molecules and is responsible for much of the behaviors of liquids.

The property of surface tension is revealed, for example, by the ability of some objects to float on the surface of water, even though they are denser than water.  Surface tension is also seen in the ability of some insects, such as water striders, and even reptiles like basilisk, to run on the water’s surface.

The Theory Behind Surface Tension

Surface tension has been well- explained by the molecular theory of matter. According to this theory, cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. The molecules well inside the liquid are attracted equally in all directions by the other molecules. The molecules on the surface experience an inward pull.

So, a network is formed against the inward pull, in order to move a molecule to the liquid surface.  It results in a greater potential energy on surface molecules. In order to attain minimum potential energy and hence stable equilibrium, the free surface of the liquid tends to have the minimum surface area and thereby it behaves like a stretched membrane.

Surface tension is measured as the force acting normally per unit length on an imaginary line drawn on the free liquid surface at rest. It is represented by the symbol T (or S). It's S.I. The unit is Nm -1  and dimensional formula is M 1 L 0 T -2.

Capillarity in Liquids

When a capillary tube is dipped in a liquid, the liquid level either rises or falls in the capillary tube.  The phenomena of rise or fall of a liquid level in a capillary tube is called capillarity or capillary action.

How do we define the surface tension of a liquid through the capillary rise method?

When a liquid rises in a capillary tube, the weight of the column of the liquid of density ρ inside the tube is supported by the upward force of surface tension acting around the circumference of the points of contact.

Thus, surface tension;

Where,  h - height of the liquid column above the liquid meniscus ρ - Density of the liquid r - Inner radius of the capillary tube θ - Angle of contact

Learning Outcomes

• Students understand the theory of the surface tension of liquids.
• Students correlate the property of surface tension with different natural phenomena.
• Students understand the concept of capillarity in liquids.
• They are able to relate surface tension and capillarity.

Materials required

• A clean and dry capillary tube
• A tipped pointer
• A beaker containing water
• A travelling microscope
• Adjustable wooden stand
• Clamps and stand

To set up the apparatus :

• Place the adjustable height stand on the table and make its base horizontal by leveling the screws.
• Fix the capillary tube and the pointer in a cork, and clamp it in a rigid stand so that the capillary tubes and the pointer become vertical.
• Adjust the height of the vertical stand, so that the capillary tubes dip in the water in an open beaker.
• Adjust the position of the pointer, such that its tip just touches the water surface.

To find the capillary rise :

• Find the least count of the travelling microscope for the horizontal and the vertical scale.
• Make the axis of the microscope horizontal.
• Adjust the height of the microscope using the height adjusting screw.
• Bring the microscope in front of the capillary tube and clamp it when the capillary rise becomes visible.
• Make the horizontal cross wire just touch the central part of the concave meniscus.
• Note the reading of the position of the microscope on the vertical scale.
• Now, carefully remove the beaker containing water
• Move the microscope horizontally and bring it in front of the pointer.
• Lower the microscope and make the horizontal cross wire touch the tip of the pointer.
• Corresponding vertical scale readings are noted.
• The difference in the two readings (i.e., height of water meniscus and height of the tip of pointer) will give the capillary rise of the given liquid.
• We can repeat the experiment by changing the height of the wooden stand.

To find the internal diameter of the capillary tube :

• Place the capillary tube horizontally on the adjustable stand.
• Focus the microscope on the end dipped in water.
• Make the horizontal cross- wire touch the inner circle at A (fig i). Note microscope reading on the vertical scale.
• Raise the microscope to make the horizontal cross wire touch the circle at B (fig ii). Note the vertical scale reading.
• The difference between the two readings will give the vertical internal diameter (AB) of the tube.
• Move the microscope on the horizontal scale and make the vertical cross wire touch the inner circle at C (fig iii). Note microscope reading on the horizontal scale.
• Move the microscope to the right to make the vertical cross wire touch the circle at D  (fig iv). Note the horizontal scale reading.
• The difference between the two readings will give the horizontal internal diameter (CD) of the tube.

• We can calculate the diameter of the tube by calculating the mean of the vertical and horizontal internal diameters. Half of the diameter will give the radius of the capillary tube.

Observations

Least count of the travelling microscope = Value of one MSD / Number of divisions on the Vernier

Mean h = ……….......... cm

= ............. ×10 -2  m

Calculations

Density of water at observed temperature, ρ = ............ kgm -3

Angle of contact of water in glass, θ   = 8 o

Note the values of  h in the first table and r in the second table for each capillary tube separately  and find the value of T in each case.

Surface tension ,

= .................. N/m

Surface tension of water  is ………………… N/m

Viva-Voce [Surface Tension]

Q.1: Define surface tension?

Ans. “The tangential cohesive force acting along the unit length of the surface of a liquid”

Where F = total force along a line

L = length of the line

In this experiment:

F = m g = weight of the pan + weight in the pan.

L = 2 (length of the slide) + 2 (breadth of the slide).

Sometime we neglect the breadth since it is very small.

Q.2: What are units of surface tension in C.G.S. and S.I. (M.K.S.) system?

Ans. Dynes / cm (C.G.S.)

Newton / meter (M.K.S.)

  Q.3: What are cohesion and adhesion force?

Ans. Cohesion force is the attractive force between like molecules, whereas, the adhesion is the

attractive force between unlike molecules, e.g. attraction between glass slide and the liquid.

Q.4: What are the factors affecting the surface tension?

Ans. (a) Nature of liquid (b) Nature of the surface in contact (c) Temperature

 Q.5: What is the effect of temperature on the surface tension?

Ans. Surface tension decreases with the rise of temperature.

Q.6: Define critical temperature.

Ans. The temperature at which the surface tension is zero.

Q.7: Why the free surface of water is concave but that of mercury is convex?

Ans. The free surface of water is concave because:

Cohesion force between water molecules >> adhesion force between water and gas molecules

Because the free surface of mercury is convex because Cohesion force >> adhesion force

Q.8: What is the shape of free surface at critical temperature?

Ans. At critical temperature the surface tension because zero hence the free surface is flat.

Q.9: Why the surface of the slide should not be oily?

Ans. The surface tension will decrease.

Q.10: Define angle of contact ?

Ans. Angle of contact, for a pair of solid and liquid, id define as

“the angle between tangent to the liquid surface drawn at the point of contact and the solid

surface inside the liquid.”

Q.11: Give some practical applications of surface tension.

Ans. (a) A drop of falling liquid is always in spherical shape.

(b) We use oily substances to set out hairs.

(c) We use soaps and detergent for cleaning clothes.

(d) A thin layer of water over the umbrella protects us against light rain.

(e) Capillary action e.g. rising of oil in the wick of a lamp.

(f) Flying insects can walk on water surface without getting their feel wet.

Physics is one of the most important subjects in Class 12. As the CBSE exam approaches, students get busy preparing for different subjects. But an essential part of the  CBSE exam  is the practical exams which consist of 30 marks.

Students must know all the experiments along with theorems, laws, and numerical to understand all the concepts of 12th standard physics in a detailed way. Two experiments (8 + 8 marks) are asked from each section in the practical exam. The experiment records and activities consist of 6 marks, the project has 3 marks and viva on the experiment consist of 5 marks.