# CBSE Class 11 Physics Notes Chapter 11 Thermal Properties of Matter

By definition, matter or material is anything that has mass and occupies space. Everything we see around us is matter. For example, a water bottle is made up of plastic or any metal, both of which are examples of matter.

The matter has properties or characteristics, by which they can be identified. The major properties of materials can be categorized under:

• Mechanical properties of materials
• Chemical properties of materials
• Physical properties of materials
• Dimensional properties of materials
• Classification Of Material Property

### What are Thermal Properties of Matter?

Thermal properties are those properties of a material which is related to its conductivity of heat. In other words, these are the properties which are exhibited by a material when heat is passed through it. Thermal properties come under the broader topic of physical properties of materials.

Thermal properties of a material decide how it reacts when it is subjected to heat fluctuation (excessive heat or very low heat, for example). The major components of thermal properties are:

• Heat capacity
• Thermal Expansion
• Thermal conductivity
• Thermal stress
• Heat Capacity

Heat capacity of a material can be defined as the amount of heat required to change the temperature of the material by one degree. The amount of heat is generally expressed in joules or calories and the temperature in Celsius or Kelvin. In order to calculate the heat capacity of materials with a given dimension, Molar heat capacity or Specific heat capacity is used.

Heat capacity can be measured by the following formula:

$Q=mc\Theta$

is the amount of heat transferred, is the change in temperature.

### What is Thermal Expansion?

When heat is passed through a material, its shape changes. Generally, a material expands when heated. This property of a material is called Thermal Expansion. There can be a change in the area, volume and shape of the material. For example, railway tracks often expand and as a result, get misshapen due to extreme heat.

### What is Thermal conductivity

It is the property of a material to conduct heat through itself. Materials with high thermal conductivity will conduct more heat than the ones with low conductivity. Some materials do not conduct heat at all because of the insulating properties of materials.

### What is Thermal stress?

The stress experienced by a body due to either thermal expansion or contraction is called thermal stress. It can be potentially destructive in nature as it can make the material explode.

### Important Questions

• (a) The triple-point of water is a standard fixed point in modern thermometry. 2018-19 300 PHYSICS 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 abovem 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?
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.
1. Explain why :
• (a) a body with large reflectivity is a poor emitter
• (b) a brass tumbler feels much colder than a wooden tray on a chilly day
• (c) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.

For example, cracks can be seen on roads where the heat is extreme. The crack is a result of thermal stress. Refer to this link for NCERT Solutions of Thermal properties of Mass/Matter