**NCERT Class 11 Physics Thermal properties of matter - NCERT Solutions prepared for CBSE students by the best teachers in Delhi.**

**Class XI Physics**

**Ch. 11: Thermal properties of matter**

**NCERT Solutions**

Question 11.1: The triple points of neon and carbon dioxide are 24.57 K and 216.55 K respectively. Express these temperatures on the Celsius and Fahrenheit scales.

Question 11.2: Two absolute scales A and B have triple points of water defined to be 200 A and 350 B. What is the relation between TA and TB?

Question 11.3: The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law:

R = Ro [1 + á (T – To)]

The resistance is 101.6 Ù at the triple-point of water 273.16 K, and 165.5 Ù at the normal melting point of lead (600.5 K). What is the temperature when the resistance is 123.4 Ù?

Question 11.4: Answer the following:

(a) The triple-point of water is a standard fixed point in modern thermometry. Why? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale)?

(b) There were two fixed points in the original Celsius scale as mentioned above which were assigned the number 0 °C and 100 °C respectively. On the absolute scale, one of the fixed points is the triple-point of water, which on the Kelvin absolute scale is assigned the number 273.16 K. What is the other fixed point on this (Kelvin) scale?

(c) The absolute temperature (Kelvin scale) T is related to the temperature tc on the Celsius scale by

tc = T – 273.15

Why do we have 273.15 in this relation, and not 273.16?

(d) What is the temperature of the triple-point of water on an absolute scale whose unit interval size is equal to that of the Fahrenheit scale?

Question 11.6: A steel tape 1m long is correctly calibrated for a temperature of 27.0 °C. The length of a steel rod measured by this tape is found to be 63.0 cm on a hot day when the temperature is 45.0 °C. What is the actual length of the steel rod on that day? What is the length of the same steel rod on a day when the temperature is 27.0 °C? Coefficient of linear expansion of steel = 1.20 × 10–5 K–1.

Question 11.7: A large steel wheel is to be fitted on to a shaft of the same material. At 27 ‹C, the outer diameter of the shaft is 8.70 cm and the diameter of the central hole in the wheel is 8.69 cm. The shaft is cooled using edry icef. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range: ƒ¿steel = 1.20 ~ 10.5 K.1.

Question 11.8: A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at 27.0 °C. What is the change in the diameter of the hole when the sheet is heated to 227 °C? Coefficient of linear expansion of copper = 1.70 × 10–5 K–1.

Question 11.9: A brass wire 1.8 m long at 27 °C is held taut with little tension between two rigid supports. If the wire is cooled to a temperature of –39 °C, what is the tension developed in the wire, if its diameter is 2.0 mm? Co-efficient of linear expansion of brass = 2.0 × 10–5 K–1; Young’s modulus of brass = 0.91 × 1011 Pa.

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