# NCERT Class 11 Physics Chapter 11 Thermal Properties of Matter CBSE Board Sample Problems

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## LA

**Question 22:**

We would like to prepare a scale whose length does not change with temperature. It is proposed to prepare a unit scale of this type whose length remains, say 10 cm. We can use a bimetallic strip made of brass and iron each of different length whose length (both components) would change in such a way that difference between their lengths remain constant. If and , what should we take as length of each strip?

**Answer:**

at all temperature

And

**Question 23:**

We would like to make a vessel whose volume does not change with temperature (take a hint from the problem above). We can use brass and iron to create a volume of 100 cc. How do you think you can achieve this.

**Answer:**

Iron vessel with a brass rod inside

**Question 24:**

Calculate the stress developed inside a tooth cavity filled with copper when hot tea at temperature of is drunk. You can take body (tooth) temperature to be and , bulk modulus for copper .

**Answer:**

This is about times atmospheric pressure.

**Question 25:**

A rail track made of steel having length is clamped on a railway line at its two ends (Fig 11.3). On a summer day due to rise in temperature by , it is deformed as shown in figure. Find *x* (displacement of the centre) if .

**Answer:**

**Question 26:**

A thin rod having length at and coefficient of linear expansion has its two ends maintained at temperatures and , respectively. Find its new length.

**Answer:**

Method I

Temperature q at a distance *x* from one and (that at ) is given by : linear temperature gradient.

New length of small element of length

Now new length

Integrating

Method II

If temperature of the rod varies linearly, we can assume average temperature to be and hence new length

**Question 27:**

According to Stefan’s law of radiation, a black body radiates energy from its unit surface area every second where *T* is the surface temperature of the black body and is known as Stefan’s constant. A nuclear weapon may be thought of as a ball of radius When detonated, it reaches temperature of and can be treated as a black body.

(a) Estimate the power it radiates.

(b) If surrounding has water at , how much water can of the energy produced evaporate in s?

(c) If all this energy U is in the form of radiation, corresponding momentum is *p = U/c*. How much momentum per unit time does it impart on unit area at a distance of 1 km?

**Answer:**

(i)

(ii)

(iii)