Question:

A rod of length 20 cm is made of metal . It expands by 0.075 cm when its temperature is raised from $0^{\circ} C$ to $100^{\circ} C$ . Another rod of a different metal B having the same length expands by 0.045 cm for the same change in temperature . A third rod of the same change in temperature . A third rod of the same length is composed of two parts , one of metal A and the other of metal B. This rod expands by 0.060 cm for the same change in temperature . The portion made of metal A has the length :

Updated On: Jul 6, 2022
  • 20 cm
  • 10 cm
  • 15 cm
  • 18 cm
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The Correct Option is B

Solution and Explanation

Let $l _{1}$ be the length of potion of metal $A$ and $l _{2}$ be the length of portion of metal $B$. Thus $l_{1}+l_{2}=20 cm$ For the given change in temperature, change in length $\propto$ intial length of rod. Hence $\Delta l _{1}=0.075 \frac{ l _{1}}{20}$ And $\Delta l _{2}=0.045 \frac{ l _{2}}{20}$ Thus $\Delta l _{1}+\Delta l _{2}=0.060$ Solving for $l_{1}$ gives $ l_{1}=10 cm $
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Notes on thermal properties of matter

Concepts Used:

Thermal Properties of Matter

Anything that has mass or occupies space in the universe is commonly known as matter. There are five properties of matters namely chemical, mechanical, thermal, dimensional, and physical properties.

Read More: Thermal Properties of Matter

Heat Capacity:

The quantity of heat needed to change the temperature of the matter by 1° is known as the heat capacity of a material. The temperature is indicated in kelvin or Celsius and the amount of heat is shown in calories or joules. Specific heat capacity or molar heat capacity is used to calculate the heat capacity of the matter with the stated dimension.

Linear expansion is the situation when change takes place in one dimension or dimensional.

Thermal Expansion:

When heat is passed through the material, the change in the area, volume, and shape is recognized as the thermal expansion property of the material. The expansion of the railway tracks due to maximal heat which leads to accidents is an example of thermal expansion.

Thermal Conductivity:

This property is interconnected to the conductivity of heat. The amount of heat regulated by the material is directly proportional to the conductivity of the material. Not all objects have the capacity to conduct heat throughout their bodies. Insulators are such objects which do not have the property to conduct heat throughout their body.

Thermal Stress:

The stress due to thermal contraction or expansion of the body is known as thermal stress. The explosion of materials takes place due to thermal stress which is dangerous. The cracks on the truck tyres are caused by an outcome of thermal stress. Trucks at high speed generate heat which is caused by the friction of the truck tyres and the road surface.