Friday, February 8, 2008

IIT JEE Physics Formula Revision 23. Heat and Temperature

1. conversion formula is F = 32 + 9C/5

2. The temperature of triple point of water is assigned a value of 273.16 K

The temperature of ice point on the ideal gas scale is 273.15 K and of the steam point is T = 373.15 K. The interval between the two is 100 K.

Centigrade scale or Celsius scale is defined to have ice point at 0°C and steam point at 100°C. The interval is 100°C.

Hence if θ represents the Celsius or centigrade temperature

V = T – 273.15 K

3. Ideal gas equation

pV = nRT

n = the amount of gas in moles
R = universal constant = 8.314 J/mol-K

Thermal expansion

Average coefficient of linear expansion

Average (α) = (1/L)*∆L/∆T

Coefficient of linear expansion at temperature T
α = Lim (∆T->0)(1/L)*∆L/∆T = (1/L)dL/dT

Suppose the length of a rod is L0 at 0° C and Lθ at temperature θ measured in Celsius. If α is small and constant over the given temperature interval,

α = Lθ-L0/L0*θ or

Lθ = L0(1+αθ)

The coefficient of volume expansion is defined in a similar way.

γ = (1/V)dV/dT

It is also known as coefficient of cubical expansion.

Vθ = V0(1+γθ)

γ = 3α

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