Physics Experiment: Factor Affecting the Rate of Loss of Heat of the Liquid
Temperature difference: Large the difference in temperature of the liquid to the surrounding more will be the rate of cooling) so increasing the temperature is proportional to the rate of reaction taking place.
In this experiment, we will go through the factors affecting the rate of heat loss of liquid or on which factors the rate of cooling of a liquid depends. The factor affecting the temperature of any body or rate of reaction is
Cooling medium: In the conduction process rate of cooling is very fast, while a very slow rate of cooling occurs in the convection process as in this movement, actual movement of medium particles takes place.
Surface area: Larger the surface area, fast will be the rate of cooling or the rate of loss of liquid and vice versa.
Thermal conductivity: Thermal conductivity of material decides the loss of heat in the surrounding. Good conductors (black painted material), conduct more heat and thus increase the rate of cooling and rate of loss of heat of liquid and vice versa.
Surface Tension Depends on Which Factors?
Lists the factors affecting the surface tension: With the increase of temperature, the surface starts to decrease as the force between liquid starts to decrease from the surface of the liquid container thus the rate of reaction increases and the reaction proceeds in the forward direction. List the factors affecting the surface tension, temperature, surrounding environment, and nature of the liquid.
Table of Content
Aim
Apparatus Required
Theory
Procedure
Observation
Graph
Result
Precautions
Lab Manual Questions
Viva Questions
Practice-Based Questions
Aim
To study the factor on which the rate of loss of heat of liquid depends.
Apparatus Required
Two Calorimeters A and B of Different Areas (Within Double-Spaced Enclose)
Two Stands for Support Thermometers
Two Thermometers
A Burner to Heat Water
A Stopwatch
Stirrer
Wooden Lids to Close the Two Calorimeters
Liquid (Water)
Theory
According to Newton’s Law of Cooling, the rate of loss increases with an increase in a temperature difference (temperature of liquid – temperature of surrounding) or increasing the temperature is proportional to rate of reaction and vice versa. In other words, we can say that rate of loss of heat (rate of cooling) is directly proportional to temperature differences such as
\[dQ/dt\text{ }\propto (T-T_{\circ})\]
\[dQ/dt\text{ }=\text{ }K(T-T_{\circ})\]
Where dQ/dt is the rate change of heat, K is the proportionality constant, T is the temperature of the liquid and \[T_{\circ} \]is the temperature of the surroundings.
Diagram
Physics experiment– Factor affecting the rate of loss of heat of the liquid Heating rate has a great influence on the curve.
Procedure
In the first step to set up the calorimeter fill the enclosure by filling the space between the double wall with water.
Now add two third hot (about \[80{}^\circ C\]) water in the two calorimeters (A and B).
Put the calorimeter inside the enclosure and stirred hot water constantly so that heat spreads uniformly. And cover the calorimeter with a wooden lid to resist the escape of heat of the calorimeter.
Now support the thermometer through the stand. One thermometer is inside the enclosure and another one is inside the two third water of the calorimeter.
Note the least count of both the thermometer and stopwatch (graph between time and temperature) and set the stopwatch at 0.
Initially notice the temperature of the water inside the calorimeter (with constantly starring) and enclosure.
As soon as the temperature of the water reaches about \[70{}^\circ C\], (at starting temperature falls rapidly) note that reading and start the stopwatch.
With constantly stirring notes the temperature of the water after every minute and note the enclosure temperature after every five minutes.
At the point where the falling temperature of the water becomes slow, start to take readings of temperature after two minutes and then after 5 minutes.
As soon as the temperature falls very slow, stop reading and plot the graph for temperature which indicates the heating rate has great influence on the curve.
Activity 1: Follow the process for one small and one large area calorimeter (different surface area of calorimeter) with the same water and the same volume of water.
Activity 2: Follow the same steps for the two same calorimeters which are black-painted outside (different material) for the same water and its volume.
Activity 3: Follow the same step for the same volume of water in similar calorimeters of different materials (conductivity difference).
Observations
The least count of enclosure water thermometer= -------- \[{}^\circ C\]
Least count calorimeter water thermometer = ---------\[{}^\circ C\]
The least count of stopwatches = -------- s
Table for Activities
Graph
Heating rate has a great influence on the curve. Greater the surface area (area factor), dark painted calorimeter (nature of surface) and conduction material or metallic material (material of surface), all cause higher rate of cooling or increase rate of loss of heat.
Result
Activity 1: The rate of cooling of liquid increases with an increase in the surface area of the calorimeter (so that more heat can transfer) and vice versa. Thus the rate of cooling liquid is directly proportional to the surface area of the calorimeter.
Activity 2: The rate of cooling also depends on the nature of the colorimeter. The black of printed calorimeters increases the rate of cooling (as black color is a good absorber and good emitter).
Activity 3: The rate of loss of heat is directly proportional to the conductivity of the material (calorimeter). Large the conductivity of material, more heat will transfer and thus, the rate of cooling increases and vice versa.
Precautions
The thermometer in calorimeter water and enclosure water should not touch to the bottom of the material.
Don’t forget to start the hot water to cool it uniformly, keep your eyes on the stop clock and start the stop clock around \[70{}^\circ C\].
Lab Manual Questions
1. What factors affect the rate of loss of liquid?
Ans: Area, nature and material of the calorimeter affects the rate of loss of liquid.
2. What are the types of heat loss?
Ans: Heat loss through conduction, convection and radiation.
3. Can the rate of loss of liquid be the same for two liquids?
Ans: Yes, the rate of reaction can be the same for two liquids if material, nature, and area of calorimeter and all conditions are the same for two liquids.
4. Lists the factors affecting the surface tension.
Ans: Temperature, nature of given liquid and surrounding environment are the factors which mainly affect the surface tension.
5. Very slow rate of cooling occurs in which process?
Ans: In convection process
Viva Questions
1. What is the unit of heat loss?
Ans: Heat loss is measured as Watts.
2. Is heat loss negative or positive?
Ans: Heat loss is negative while heat evolved is positive.
3. Does thickness affect heat loss?
Ans: Yes, greater the thickness of material less will be the rate of heat loss and vice versa.
4. Two variables needed to draw the graph for heat loss?
Ans: Graph of heat loss (heating rate has a great influence on the curve) is determined by change in temperature with time or can say temperature and time are the two variables which are needed for a graph for heat loss.
5. Very slow rate of cooling occurs in which process?
Ans: In the conduction process rate of cooling is very fast while very slow rate of cooling occurs in the convection process as in this movement actual movement of medium particles takes place
6. How does a lid prevent heat loss?
Ans: Lid helps to close the path for heat transfer or can say lid acts as an insulation so that rate of heat loss decreases.
7. Which material is best at conducting heat?
Ans: Most metals are very good conductors of heat or can say material with free electrons conduct heat easily as compared to material without or less free electrons.
8. Boiling of water is what type of heat loss?
Ans: Convection in which water molecules move from high pressure region to low pressure region.
9. On which factor does cooling of water depend?
Ans. Temperature difference, thermal conductivity, surface area, medium, and surface tension.
10. Surface tension depends on which factors?
Ans. List the factors affecting the surface tension,
temperature, surrounding environment, and nature of liquid.
Practical Based Questions
1. Heat transfer takes place according to which of the following laws?
a. Newton’s second law of motion
b. First law of thermodynamics
c. Newton law of cooling
d. Second law of thermodynamics
Ans: Second law of thermodynamics.
2. For conduction heat transfer, the heat energy propagation will be minimal for
a. Copper
b. Air
c. Water
d. Lead
Ans: Air
3. Heat is transmitted from higher to lower temperature by actual movement of molecules in
a. Convection
b. None of these
c. Conduction
d. Radiation
Ans: Convection
4. Good absorber of heat are
a. Poor emitter
b. Good emitter
c. Non emitter
d. None of these
Ans: Good emitter
5. 300 gm of water at \[25{}^\circ C\] is added to 100g of ice at \[0{}^\circ C\] . The final temperature of the liquid is
a. \[0{}^\circ C\]
b. \[5{}^\circ C\]
c. \[15{}^\circ C\]
d. \[25{}^\circ C\]
Ans: \[0{}^\circ C\]
6. The heat of sun come to earth through
a. Convection
b. Conduction
c. Radiation
d. Evaporation
Ans: Radiation
7. Among the following method, gravity does not play any role in
a. Convection
b. Radiation and conduction
c. Radiation
d. Conduction and convection
Ans: Radiation and conduction
8. Rate of conduction of heat depends on
a. Area of cross section
b. Temperature difference
c. Properties of material
d. All of these
Ans: All of these
Conclusion/Summary
With the increase in surface area which is in contact with the hot body will increase the rate of loss of heat or rate of cooling by allowing the large number of vibrating and hot molecules or atoms. And also if the material is conducting then the heat transfer and rate of heat loss increases and the body cools down easily. Also, the color of the material affects the rate of cooling. Black color (as black body) has tendency to absorb whole heat radiation and thus cool down the body which is in contact with it (increases the rate of cooling).
FAQs on To Study the Factors Affecting the Rate of Loss of Heat of the Liquid
1. What are the main factors that affect the rate of loss of heat from a liquid as per the CBSE Class 12 syllabus for 2025-26?
For the Class 12 board examinations, the following factors are considered important in determining the rate of loss of heat from a liquid:
- Temperature Difference: The rate of heat loss is directly proportional to the difference in temperature between the liquid and its surroundings. A larger difference leads to faster cooling.
- Nature of the Exposed Surface: A dull, black surface radiates heat more effectively than a shiny, polished surface. Therefore, a liquid in a blackened vessel cools faster.
- Area of the Exposed Surface: A larger surface area allows for a greater rate of heat transfer (conduction, convection, and radiation) to the surroundings, leading to quicker cooling.
- Nature of the Liquid: Different liquids have different specific heat capacities. A liquid with a lower specific heat capacity will cool down faster for the same rate of heat loss.
2. State Newton's Law of Cooling. What are the essential conditions under which this law is applicable?
Newton's Law of Cooling states that the rate of loss of heat of a body is directly proportional to the difference in the temperature of the body and its surroundings, provided the temperature difference is small.
The essential conditions for its applicability are:
- The temperature difference between the body and the surroundings must be small (typically less than 30-40°C).
- Heat loss should occur predominantly through convection and radiation.
- The surrounding temperature must remain constant during the cooling process.
- The surface area and nature of the cooling surface must not change.
3. Why is it an important precaution to continuously stir the liquid in a calorimeter while studying its rate of cooling?
Continuously stirring the liquid is a crucial step in the experiment for a very specific reason. Without stirring, the liquid at the top and near the walls of the calorimeter will cool faster due to contact with air and the calorimeter walls. This creates a non-uniform temperature distribution within the liquid. Stirring ensures that the heat is distributed evenly throughout the liquid, and the thermometer records the average temperature of the entire liquid at any given instant. This provides an accurate measurement for plotting the cooling curve and verifying Newton's Law.
4. How can you experimentally verify Newton's Law of Cooling using a graph? What is the expected shape of the graph?
To experimentally verify Newton's Law of Cooling, you would:
- Heat a liquid in a calorimeter to about 80°C and place it in an enclosure at a constant room temperature.
- Record the temperature of the liquid at regular one-minute intervals until it cools by about 25-30°C.
- Plot a graph of temperature (T) on the y-axis against time (t) on the x-axis. This is the cooling curve, which will be an exponential decay curve.
- To verify the law, plot a graph of the rate of cooling, dT/dt (calculated from the cooling curve's slope), against the excess temperature (T - T₀), where T₀ is the surrounding temperature.
- This verification graph should be a straight line passing through the origin, which confirms that the rate of cooling is directly proportional to the temperature difference.
5. A cup of hot tea cools faster on a windy day than on a calm day. Which factor affecting the rate of heat loss is demonstrated here?
This phenomenon demonstrates the effect of convection on the rate of heat loss. On a calm day, the air layer just above the tea gets heated, becomes less dense, and rises, allowing cooler air to take its place. This is natural convection. On a windy day, the movement of air (wind) continuously replaces the warm air layer above the tea with cooler air. This process, known as forced convection, significantly increases the rate at which heat is carried away from the tea, causing it to cool much faster.
6. Why is Newton's Law of Cooling considered a special case of the Stefan-Boltzmann Law? What is the key assumption made?
Newton's Law of Cooling is an approximation of the more fundamental Stefan-Boltzmann Law, which governs heat loss by radiation. The Stefan-Boltzmann Law states that the rate of heat loss is proportional to (T⁴ - T₀⁴), where T is the body's temperature and T₀ is the surrounding's temperature (in Kelvin).
The key assumption is that the temperature difference is small. When (T - T₀) is small, the term (T⁴ - T₀⁴) can be mathematically approximated using the binomial theorem to be proportional to (T - T₀). This approximation simplifies the complex radiation law into the linear relationship described by Newton's Law, making it valid only under conditions of small temperature differences.
7. For a 3-mark question, how would you compare the rate of cooling of two identical liquids in identical calorimeters, one painted black and the other polished silver?
To answer this for 3 marks, you should structure it as follows:
- Point 1 (Principle): The rate of cooling is influenced by the nature of the radiating surface. The emissive power of a surface determines how efficiently it radiates heat.
- Point 2 (Comparison): A surface painted black has a high emissivity and is an excellent radiator of thermal energy. A surface that is polished silver has a very low emissivity and is a poor radiator of heat.
- Point 3 (Conclusion): Therefore, the liquid in the black-painted calorimeter will lose heat to the surroundings at a much faster rate through radiation compared to the liquid in the polished calorimeter. As a result, its temperature will drop more quickly, and it will cool down faster.
