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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
| No | Radius of the water meniscus | Reading at tht tip of pointer | Height, h = h -h (cm) | ||||
| M.S.R. (cm) | V.S.R. (div.) | Total = MSR+(VSR×LC) h (cm) | M.S.R. (cm) | V.S.R. (div.) | Total = MSR+(VSR×LC) h (cm) | ||
| 1 | |||||||
| 2 | |||||||
| 3 | |||||||
| 4 | |||||||
| 5 | |||||||
Mean h = ……….......... cm
= ............. ×10 -2 m
| Microscope readings for cross wire in position, | Internal diameter | Internal radius, | |||||
| A (cm) | B (cm) | C (cm) | D (cm) | Vertical, Y= B-A (cm) | Horizontal, X=D-C (cm) | Mean, | |
|
| |||||||
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.
COMMENTS
Place the penny, heads up, on top of a paper towel. 3. Hold your dropper about 1-inch above the penny and add drops of water to the surface of the penny until it overflows. 4. Record the number of drops of water the surface of the penny can hold in the table on the next page under the column labeled "Run 1.". 5.
The coefficient defines the surface tension in the units of J m2 = N m-1. Each liquid is characterized by its own surface tension, which decreases with an increasing temperature. The energetic definition of the surface tension (equation 1) is not the only way to describe it. We can derive it also from the simple experiment shown in Figure 2.
molecules on the surface of a bowl of water are attracted to each other as well as to the water below them, which creates a strong and flexible film on the water's surface. This is the surface tension that allows the paperclips to float. When you add soap to water, however, the surface tension breaks. Soap molecules consist of
s to move upward through a narrow tube. The attraction of water to the walls of a tube sucks the water up more strongly than gravity pulls it down (i.e. wate. moving up a plant's roots and stem). Surface tension is a property of a liquid that allows them to resist external for.
drops formed by volume v of the two liquids, then their surface tensions are related as ¥ 1 /¥ 2 = (d 1 /d 2)*(n 2 /n 1) One of the liquid is water its surface tension and density are known.Then te surface tension of the given liquid can be calculated. Procedure: 1. Clean the stalgmometer with chromic acid mix, wash with water and dry it 2.
SURFACE TENSION EXPERIMENT: Measuring the surface tension using the 'break-away' method. OBJECTIVE: 1. Creating a liquid layer between the edge of a metal ring and the surface of the liquid. 2. Measuring the tensile force acting on the metal ring just before the liquid layer breaks away. 3. Determining the surface tension from the measured ...
This experiment involves a simple method to determine the surface tension of a liquid, which in our case is water, by analyzing a drop formed at the edge of a tube containing the liquid. This technique is called the Pendant Drop Method since the liquid drop ... Surface tension is also the cause of capillary action and the presence of meniscuses. 3.
surface tension that you can try yourself. Figure 3 This apparatus, consisting of a C-shaped wire frame and a wire slider, can be used to measure the surface tension of a liquid. Table 1 Surface Tensions of Common Liquids Liquid Surface Tension γ (N/m) Benzene (20 °C) 0.029 Blood (37 °C) 0.058 Glycerin (20 °C) 0.063 Mercury (20 °C) 0.47
SURFACE TENSION AIM: To determine the surface tension of water using the 'break-away' method. To Do: 1. Creating a liquid layer between the edge of a metal ring and the surface of the liquid. ... When you finish experiment leave the dynamometer at zero force so that there is no tension in the spring. Author: user Created Date: 2/27/2023 3 ...
Purpose: To learn about the surface tension of various liquids and how it can be changed. Learning Objectives: 1. Understand that surface tension is a property of a liquid that helps things float on top of the surface. 2. Know that different liquids have different surface tensions 3. Learn that surface tension can be altered by adding other ...
surface. 2. Touch the tip of a clean Q-tip to the middle of the surface. Record how much the pepper moves, on a scale of 0 (no motion at all) to 5 (moved fast and far). The clean Q-tip is your control (something with which to compare the rest of the experiment). 3. Dip a Q-tip into each of the 4 fluids provided and touch the tip to the center ...
pty and rinse your bowl.• Fill the bowl back up wit. about an inch of water.• Sprinkle pepper e. enly across the surface. Again take a minute to observe how the p. pper moves in the water.• Carefully dip the end of a clean toothpick. into dishwashing liquid.• Dip the dishwashing liquid end of the toothpick into t.
Surface tension is a property of liquids in which molecules of one substance are more attracted to each other than to molecules of another substance. 4. Water is unique in that it has a high surface tension compared to other liquids. We observe this when water beads up on glass.
Place the penny, heads up, on top of a paper towel. 3. Hold your dropper about 1-inch above the penny and add drops of water to the surface of the penny until it overflows. 4. Record the number of drops of water the surface of the penny can hold in the table on the next page under the column labeled "Run 1.". 5.
Experiment 4 Surface tension I. Introduction The term surface is used when referring to either a gas-solid or a gas-liquid interface. The tension in the surface is the force per unit length that must be applied to the surface so as to counterbalance the net inward pull. It has the units of dyne/cm. as shown in Figure 1.
The surface tension is denoted as . Quantitatively, it may be defined, in SI units, as the force in newtons (N) acting at right angle to any line of one metre length along the surface of the liquid. Since, the force in newtons acts along a distance of one metre, the unit of surface tension is expressed as N m-1.
material. Surface tension creates a finite jump in pressure across the interface, but the typical magnitude of surface tension limits its influence to fluid bodies much smaller than the huge planets and stars discussed in the preceding chap-ters. When surface tension does come into play, as it does for a drop of water
h: `c = (σ/(ρg))1/2. For an air-water surface, for example, σ ≈ 70 dynes/cm, ρ = 1 g/cc and g = 980 cm/. 2, so that `c ≈ 2mm. Bodies of water in air are dominated by the influence of surface tension provided they are smaller tha. the capillary length. Roughly speaking, the capillary length prescribes the maximum size of pendant drops ...
Each group was provided with a table of surface tension values for pure water as a function of temperature. The temperature in the room was noted, and the corresponding reference surface tension value was recorded. For the day of the experiment, the students used a standard surface tension value of 72 mN/m for a recorded room temperature of 25 °C.
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.
Surface Tension . Paper Experiment . 1. Write in each object and circle what happened to it when you placed it on the different types of paper. Object 1: _____ Object 2 : _____ Object 3 : Type of Paper Prediction Result Prediction Result Prediction Result . Printer . Falls through ...
on and the paperclip sinks.Appendix of Info for Us Grown-Upso Water has such high surface tension, cohesive, a. d adhesive properties because of its ability to form H. bonds. In bulk water, each water molecule can form 4 H-bonds. When adhering to other surfaces, dispersive forces allow water to make weak bonds with othe. materials; thi.
Surface tension is a meaningful parameter influencing boiling and condensation in macro-scopic scale, in confined spaces, or for nanofluids; it further affects boiling with surfactants.