Q. 1 B5.0( 5 Votes )

Who is telling the truth?

a. The temperature of a substance is measured in Joules.

b. Heat flows from an object at a higher temperature to an object at a lower temperature.

c. Joule is the unit of heat.

d. Objects contract on heating.

e. Atoms of solid are free

f. The average kinetic energy of atoms in a hot object is less than the average kinetic energy of atoms in a cold object.

Answer :

(a) the statement is a lie.


Explanation: Temperature is the measurement of the degree of hotness of a body. Celsius (°C), Fahrenheit (°F), and Kelvin (K) are three different units usually used to measure temperature in daily life situations. Joules is the SI unit of work or energy. Temperature and heat energy are related, but they are not the same.


(b) the statement is true.


Explanation: Every object has a tendency to equalize its temperature with its surroundings. For that, there should be a movement of heat energy. The natural tendency of heat energy is to flow from a region of high temperature to a region of lower temperature.


Consider the example of a hot tea which becomes cooler on placing in a cold room. As heat energy moves from tea at high temperature to room at a lower temperature and as a result, tea becomes cooler. There must be a source of external energy to increase the temperature of a hot body placed in cooler surroundings.


(c) the statement is true.


Explanation: Heat is a form of energy. It denotes the amount of kinetic energy possessed by the atoms or molecules in an object. So, a large amount of heat implies the larger kinetic energy of atoms or molecules in that system. Joule is the SI unit of energy. Since heat is nothing but the amount of thermal energy, heat can be measured in Joules.


(d) the statement is a lie.


Explanation: Heat energy denotes the amount of average kinetic energy of atoms or molecules in a body. On supplying heat energy to a body, atoms or molecules gain that energy and will utilize to increase their kinetic energy. Increase in kinetic energy of atoms or molecules will increase their velocity of motion. This will reduce the attractive force between neighboring atoms or molecules.


The decrease in attractive force will increase the separation between neighbouring atoms or molecules. It results in the expansion of the object. For contraction, the separation between neighbouring particles should decrease. For this kinetic energy of particles should decrease. It happens when heat energy flows out of the object or temperature decreases.


(e) the statement is false.


Explanation: In case of solids, atoms are very closely packed. There exists a very strong interatomic force. This restricts the free motion of atoms. That is why the solids have a fixed shape and size. In case of fluids, atoms or molecules can move freely. That’s why it has no fixed shape.


(f) the statement is true.


Explanation: Heat energy is the sum total of all kinds of kinetic energies of atoms or molecules in a body. This means a body with high kinetic energy must have a high value of average kinetic energy. Temperature is a measure of average heat energy possessed by an object. An object at higher temperature should have higher thermal energy and thereby higher average kinetic energy than an object at a lower temperature.


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