# Physics 312 Lecture: "Transfer of heat by Conduction" May 14, 1998

• Conduction is one mechanism by which heat can be transferred from one object to another (the others are convection and radiation).
• When one end of a material is heated, the atoms there move more quickly (or vibrate more quickly in place); they jostle neighbors, and so forth, transferring energy through the material.
• Thermal conductors move heat rapidly: they have large values of thermal conductivity "k"; thermal insulators transmit heat slowly: they have small values of "k"
• Heat is transferred by conduction at a rate
```           dQ/dt = - k * A * dT/dx
```
• In a uniform medium, the gradient "dT/dx" may be replaced by "delta_T / length"
• When several layers of material with different thermal conductivity are sandwiched together, the overall heat flow rate may be determined by calculating the overall "R-value"
```                      R(tot) = sum of L/k
```
and using it in the equation
```           dQ/dt =  A * delta_T / R(tot)
```

This lecture discusses material in Chapter 20 of Serway.