Thermal, Boiling, Melting

Thermal Conductivity

Process of thermal conduction through solid

Vibrations of atoms or molecules of the solid • Solid - composed of atoms or molecule • Room temperature – vibration (equilibrium) • Heating – increase the vibration and amplitude (neighborhood atom/molecules) • Higher amplitude - higher kinetic energy • Meaning – Energy travel through solid (Called thermal conduction) • Medium of thermal conduction – Metallic (high) & nonMetallic (low)

Movement of free electrons in the solid

• At room temperature electron move freely. • Heat - add energy to electron (higher kinetic energy, more speed ) • Collide with neighborhood electron and impart the energy.

• Thermal Conductivity = heat × distance / (area × temperature gradient) λ = Q × L / (A × ΔT)

Material

Thermal Conductivity W/m, oK

Thermal Conductivity (cal/sec)/(cm2, oC/cm)

Air at 0 C

0.024

0.000057

Aluminum

205.0

0.50

Brass

109.0

-

0.8

0.002

385.0

0.99

Glass, ordinary

0.8

0.0025

Gold

310

-

Ice

1.6

0.005

Iron

-

0.163

Lead

34.7

0.083

Polyethylene HD

0.5

-

Polystyrene expanded

0.03

-

Silver

406.0

1.01

Styrofoam

0.01

-

Steel

50.2

-

-

0.0014

0.12-0.04

0.0001

Concrete Copper

Water at 20 C Wood

Electrical Conductivity

Conduction of electric in metal • Electron - subatomic particle of atom. • Carry a negative electrostatic charge. • Movement (atom to atom) - random & under certain condition • Electromotive force – direct the electron movement • This directional movement of electrons due to an electromotive force is what is known as electricity.

Electrical conductivity - The easiness of electron removed from the atom / ability of a material to carry the flow of an electric current (a flow of electrons). Different matter - different rate of electrical conductivity.

How to measure the electrical conductivity?

Think about their conductivity • Which one is the best electric conductor? • Carbon, Silver, Iron, aluminum

Boiling & Melting Point

• When solid substance is heated (reach specific temperature) at which it begins to melt (become liquid). This is it's melting point. • When a liquid is cooled, it reaches a temperature at which it begins to freeze (become solid). This is its freezing point • Melting point = freezing point

• When a liquid is heated, it will reach a temperature at which it begins to become a gas. This is it's boiling point.