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Basic Science & for Railway ALP CBT2 Temperature INDIA Engineering RRB ALP & Technicians Recruitment 2018

Thermal Expansion The increase in the dimensions of a body due to the increase in its temperature is called thermal expansion. The thermal expansion of solid is classified as follows: 1. Linear Expansion On increasing the temperature of a solid, its length increases. This increase in length of a solid on heating is called linear expansion. The fractional increase in length per C rise in temperature is called coefficient of linear expansion

1. Linear Expansion On increasing the temperature of a solid, its length increases. This increase in length of a solid on heating is called linear expansion The fractional increase in length per C rise in temperature is called coefficient oflinear expansion. de coefficient of linear expansion, If is coefficient of linear expansion at t1oC then, 21 - length of the rod at t C 22 - length of the rod at t2 C 11 11 [1 + (t2-ti) then,

2. Superficial Expansion In increasing the temperature of a solid, its area increases. This increase in area is referred as superficial expansion. If the area of solid at temperature t C is A and on heating the rod, the area becomes A2 at t2 C then, where is called coefficient of superficial expansion at t loc Coefficient ofsuperficial expansion is defined as the fractional increase in area per "C rise in temperature. / AT dA A.dT i.e., Coefficient of areal expansion

3 Cubical Expansion In increasing the temperature of a solid, its volume increases This increase in volume with increase in temperature is called cubical or volume expansion. IfV1 is the volume of a solid at temperature t, C and on increasing the temperature tot2 C the volume becomes V2 then, . where is coefficient of volume expansion at t oc Coefficient of volume expansion is defined as the fractional increase in volume per "C rise in temperature. dV i.e., Coefficient of volume expansion, Relation between coefficient of linear expansion ( ), coefficient of superficial expansion (B) and coefficient of cubical expansion : : 1:2 :3 2 3

Applications of Thermal Expansion in Solids (i) Bimetallic strip: If two strips of different metals are welded together to form a bimetallic strip, when heated uniformly it bends in the form ofan arc, the metal with greater coefficient of linear expansion lies on convex side. 0 At tc

At t1 c tiOc R. The radius of arc thus formed by bimetal is, or R where t temp. difference between the two ends. d-thickness of each strip oi and 2 are coefficients of linear expansion of two different metals.

(ii) Thermal stress in a rigidly fixed rod: Thermal strain- li 2 stress In elasticity, Young's modulus- Thermal stress-Y (t2-ti) Tensile strain ~aAt (iii) Effect of temperature on pcadulum clock: Change in time period, 7-T2-T,-- . .Ti 2

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Anant Dhiman

a year ago

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