Docstoc

THERMAL EXPANSION

Document Sample
THERMAL EXPANSION Powered By Docstoc
					     THERMAL EXPANSION

Objects undergo changes in dimension when they are heated. This change in
length or area or volume is called "Thermal Expansion".
WHY BODIES EXPAND ON HEATING
At a given temperature, inter-molecular distances are definite. When a
body is heated it's molecules vibrate more energetically against the
action of inter-molecular forces and the displacement of molecules is
increased. Since the average distance between the molecules increases,
the dimension of the body increases. Consequently body expands.
TYPES OF THERMAL EXPANSION
There are three types of thermal expansion:
 (1) Linear Expansion
 (2) Superficial Expansion
 (3) Volumetric Expansion
LINEAR EXPANSION
Expansion in length of solid bodies on heating is called linear
expansion.
FACTORS ON WHICH LINEAR EXPANSION DEPENDS
Consider a metallic bar of length "L1" at temperature "T1" k .Let the bar
is heated to "T2" k.

From experiments it is observed that linear expansion depends on two
factors:
 1. The increase in length of a solid bar is directly proportional to its
original length

2. The increase in length is directly proportional to the change in
temperature.


Combining (1) and (2)
.................
OR
............
.....
Where = Coefficient of linear expansion of solid.
FINAL LENGTH OF BAR

From figure:
....................
Putting the value of L
L2 = L1 + L1 T............
 L2 = L1 (1+ T)...............
 L2 = L1 {1+ (T2 - T1)}......
Where [T= T2 - T1]
For latest information , free computer courses and high impact notes
visit : www.citycollegiate.com
COEFFICIENT OF LINEAR EXPANSION
It is a characteristic property of a material of solid and is defined as
 " increase in length per unit original length per Kelvin rise in
temperature is known as coefficient of linear expansion".
 It is denoted by ""(alpha). Value of is constant for a given material
but different for different materials. It is independent of mass &
dimensions of body . coefficient of linear expansion depends on the
nature of material.
UNIT OF

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:11
posted:5/7/2012
language:English
pages:2