Thermal conduction is the transfer of heat within a substance without the movement of its particles. It occurs due to the transfer of kinetic energy between neighboring molecules or atoms. Metals are good conductors as they have free electrons while insulators like wood and glass are poor conductors of heat.
Chapter 10 Thermal Properties of Matter focuses on heat transfer through conduction convection and radiation. It explains the thermal expansion of solids liquids and gases along with concepts like specific heat capacity latent heat and anomalous expansion of water. Practical thermometry applications and real-world phenomena related to heat are also discussed.
Variable State in Thermal Conduction
In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usually occurs when the material is initially heated or cooled, and the temperature difference between different parts of the material is evolving over time until it reaches equilibrium.
– For instance, suppose a metal rod is heated on one end; the temperature changes at different points along the rod with time since heat is being transferred from the hot end to the cooler end. The gradient will be high in the beginning, and with the passage of time, the gradient will decrease to the point when the system achieves equilibrium.
Steady State in Thermal Conduction:
In thermal conduction, a steady state is when the temperature distribution in the material becomes constant over time. The temperature at any point in the material no longer changes, which means there is no further change in temperature with respect to time. The heat flow becomes constant, and the system has reached thermal equilibrium.
Example: For instance, if the temperature has stabilized such that no temperature variation is noticed in the rod as described earlier, then the system is in a steady state. The amount of heat going into one end is the same as the amount of heat going out the other end.
Temperature Gradient:
Temperature gradient is the measure of how temperature changes over a given distance in a material. It is defined as the rate of change of temperature with respect to distance. It is often measured in units of °C/m or K/m.
– Mathematical Expression: The temperature gradient ∇T can be mathematically expressed as:
∇T = ΔT / Δx
Where:
– ∇T = Temperature gradient (°C/m or K/m)
– ΔT = Temperature difference between two points in the material (°C or K)
– Δx = Distance between the two points (m)
In a steady-state conduction, the temperature gradient is constant and linear, so that the rate of temperature change is uniform throughout the material. In a variable state, the temperature gradient changes with time as the material approaches a new thermal equilibrium.
Click here for more:
https://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/