Page 149 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

where
.α = Coefficient of linear expansion
L1 = Initial length
L2= Final length

T1 = Initial temperature
T2 = Final temperature
Superficial or Areal Expansion
Coefficient of superficial or areal expansion is defined as the increase in area per unit area per degree rise in
temperature
The coefficient of superficial expansion is twice the coefficient of linear expansion.
Coefficient of superficial expansion = 2 x coefficient of linear expansion.

Cubical Expansion

Coefficient of cubical expansion is defined as the increase in volume per unit volume per degree rise of temperature.
Coefficient of cubical expansion is thrice the coefficient of linear expansion.
... Coefficient of cubical expansion = 3 x coefficient of linear expansion.

Note:

(1) Solids possesses all the three types of expansion.
(ii) Copper, Brass, Aluminium alloy expands more than steel/ cast iron.
(iii) Liquids and gases have only cubical expansion.
(iv) The volumetric expansion of liquids is usually significantly greater than that of solids.

(v) Water is a special case. Its volume decreases between 0°C to 4°C at which temperature, its
density is highest.
(vi) The values of coefficient of linear expansion and cubical expansions are available in logarithmic
tables, and may be used for different metals and liquids whenever necessary.

Co-efficient of expansion and related problems
1 If Iron Bridge is 100 metre long at 0 C. What will be the length of bridge if the temperature is 400 C and the
co-efficient of linear expansion is 12 x 10-6 per degree?

Initial length (l) = 8m
Increased length = 0.84 mm
Increased temperature(t) = 80 - 30 = 50C

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CITS : WCS - Electrical - Exercise 12