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Thermal expansion coefficients describe how a material expands when heated. Option A (α : β : γ = 1 : 2 : 3) is CORRECT — for isotropic solids (materials that expand uniformly in all directions): α is the linear expansion coefficient (expansion per unit length per degree), β = 2α is the area (superficial) expansion coefficient (expansion per unit area per degree), and γ = 3α is the volume (cubical) expansion coefficient (expansion per unit volume per degree). Therefore, α : β : γ = 1 : 2 : 3. This relationship is derived mathematically from the geometry of expansion: if a length increases by α per degree, a 2D area increases by approximately 2α per degree, and a 3D volume increases by approximately 3α per degree. Option B (1:3:6) is incorrect — these ratios do not correspond to any standard thermal expansion relationship. Option C (2:3:4) is incorrect — these are not the standard ratios for thermal expansion coefficients. Option D (3:2:1) is incorrect — this is the reverse of the correct order. γ > β > α, not the other way around. For exams: α is smallest (1D), β = 2α (2D), γ = 3α (3D). This is an important formula for SSC, UPSC, Railway exams.
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Heat is a form of energy that transfers between objects or systems due to a temperature difference, moving from a hotter body to a cooler one until thermal equilibrium is reached.
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