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Newton's Law of Cooling Viva Questions

Viva Questions on Newton's Law of Cooling Experiment


1. What is meant by internal energy?


Ans: The sum of kinetic and potential energies of a body is called its internal energy.


2. Define temperature.


Ans: Temperature of a body is called as the degree of coldness or hotness of the body.


3. State Newton's law of cooling


Ans: The Newton's law of cooling is defined as the rate of decrease in heat from a body is directly proportional to the mean temperature difference between the body and its surroundings.


4. What is meant by thermodynamics?


Ans: Thermodynamics is a branch of science which deals with the study of transformation of heat energy into mechanical energy and vice-versa.


5. What is absolute zero of temperature?


Ans: —273.15° C


6. What is the tripple point temperature of water?


Ans: 273.16° K or 0.01°C


7. Define isothermal process.


Ans: Isothermal process is a physical change in which pressure and volume of a system change at constant temperature (It is a slow process).


8. Define adiabatic process.


Ans: Adiabatic process is a physical change in which pressure, volume and temperature change (It is a sudden process).


9. What is meant by irreversible process?


Ans: Any process that can't be retraced in the reverse order and in the opposite sense is called an irreversible process.


10. What is meant by reversible process?


Ans: A reversible process which can be made to proceed in two opposite directions with the same case, so that the system and the surroundings pass through exactly the same intermediate state as in the direct process.


11. Name the different modes of transmission of heat.


Ans: There are three modes of transmission of heat. They are conduction, radiation and convection.


12. What is radiation?


Ans: Radiation is energy or particles that origins from a source and travels through space or other medium. It may be able to go through various materials.


eg: Light, X-ray, Sound, Microwaves and so on


13. What is Stefan-Boltzmann law?


Ans: Stefan-Boltzmann law states that the total radiant heat power emitted from a surface is directly proportional to the fourth power of the black body’s absolute temperature.


ie, j* = σT4


14. Define emissivity (or relative emittance) of a surface.


Ans: Emissivity (ε) is defined as the relative ability of a surface to emit heat by radiation. It is the ratio of radiant energy from an object’s surface at given temperature to the radiant energy of a black body at same temperature.


15. State Kirchhoff's law.


Ans: Kirchhoff's law of radiation states that at thermal equilibrium, the power radiated by an object is equal to the power absorbed by that object.


16. What is the velocity of heat radiation?


Ans: Thermal radiation or Heat radiation is the energy transfer in the form of electromagnetic waves. The velocity of thermal radiation in the vacuum is same as that of light.

c0 = n0c

where, c0 = thermal radiation velocity

n0 = refractive index of medium

c = wave velocity


17. To which part of the electromagnetic spectrum do the thermal radiation belong?


Ans: Infrared region


18. What is a black body?


Ans: A black body is a surface that absorbs all radiant energy falls on it, regardless of frequency or angle of incidence.


19. What is meant by black body radiation?


Ans: Blackbody radiation is defined as the spectrum of light emitted by any heated object. It is the radiation emitted by the black body. For example, filament of a light bulb


20. What is Wien's displacement law?


Ans: The wavelength at which the maximum radiated power for a blackbody is inversely proportional to the absolute temperature.

ie, λmax = b/T

b = constant of proportionality

T = absolute temperature


21. Aim of Newton’s law of Cooling


Ans: To study the connection of temperature of a body to the time as it cools by radiating heat.


22. Apparatus of Newton’s law of Cooling


Ans: Calorimeter and stirrer, thermometer, clamp and stand, stop-watch, hot water and so on


23. Principle of Newton’s law of Cooling


Ans: By Newton's law of cooling, rate of cooling is directly proportional to mean temperature difference between the cooling substance (water) and the surrounding.

i.e., dθ/dt (θ-θ0)

where, θ - mean temperature of the cooling substance (water)

θ0 - temperature of the surrounding

As time increases, θ decreases, (θ-θ0) decreases and hence rate of fall of temperature dθ/dt also decreases.


24. Procedure of Newton’s law of Cooling


Ans: About 2/3 rd of the calorimeter is filled with hot water of about 110°C. A thermometer is suspended inside the calorimeter from a clamp and stand. Let θ0 be the temperature of the surrounding. Water is stirred continuously to make it cool uniformly. When the temperature of hot water falls to 100°C, a stop-watch is started. For every one minute the temperature is noted. The time-temperature observation is continued till the temperature falls to say 20°C.

A graph is plotted with time along the X-axis and temperature θ along the Y-axis, The graph is known as cooling-curve of the liquid.

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