# Heat and Thermodynamics - Short Question Solution | Physics Grade XI

### Short Question Solution

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#### Viva Voice Questions # Heat and Thermodynamics - Short Question Answers 1

1. Two thermometers are constructed in the same way except that one has a spherical bulb and the other an elongated cylindrical bulb. Which one will respond quickly to temperature changes?
Ans: Thermometer with cylindrical bulb. The reason is that the area of the cylindrical surface is greater than the spherical surface and hence mercury in cylindrical bulb reaches the temperature of surrounding earlier.

2. The triple point of water is a standard fixed point in modern thermometry, why?
Ans: The triple point of a substance is unique i.e. it occurs at one particular pressure and temperature. On the other hand, the melting point of ice and boiling point of water change due to the presence of impurities in water. Hence the triple point of water chosen as a fixing point in modern thermometry.

3. On the Kelvin scale, one of the fixed points is the triple point of water which is assigned the number 273.16 K. what is the other fixed point on this scale?
Ans: To set up a temperature scale, we need two fixed points on the Kelvin scale, one fixed point is the triple point of water and the other fixed point is absolute zero.

4. What is absolute zero?
Ans: In principle, there is no upper limit of temperature. In contrast, there is a definite lower limit of the temperature. The lowest possible temperature attainable by an object is -273.15 C. This temperature is called absolute zero.

5. Why is mercury used in making thermometers?
Ans: Mercury is used in thermometer because of the following reasons;
• It does not wet the wall of the glass tube.
• It can be used over a wide range of temperatures.
• Its expansion is uniform over the ordinary range of temperatures.
• It is opaque and a shining liquid.
• It has low specific heat.

6. Explain why is platinum wire used in resistance thermometers?
Ans: Resistance thermometers use platinum wire because of the following reasons;
• The resistance of a platinum wire increases uniformly with the rise in temperature.
• For platinum the temperature coefficient of resistance is high.
• Its melting point is high.

7. How can the sensitivity of a thermometer be increased?
Ans: The sensitivity of a thermometer can be increased if the bulbs of the thermometer are constructed to have the largest surface area. Also, the capillary tube must be very thin.

8. How are gas thermometers superior to mercury thermometers?
Ans: Gas thermometers are superior to mercury thermometers because;
• The expansivities of gas thermometers are more than mercury thermometers.
• The gas thermometers cover a wide range of temperature and the expansion of gas is regular.
• Gases can be obtained in pure form.

9. Water is cheap and available everywhere but it is not used as the thermometric liquid. Why?
Ans: we cannot use water as a thermometric substance because of the following reason:
·        It has an irregular expansion.
·        Its range is very low (0◦ C to 100◦ C).
·        It wets the wall of the capillary tube.
·        It has high thermal capacity and low conductivity.
·        It has higher vapor pressure which affects the expansion.

10. How is a thermometer be calibrated?
Ans: The length of the capillary tube between the lower fixed point and the upper fixed points are divided into equal divisions according to the scale of temperature. This process is called the calibration of thermometer.

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