# PHY 1321 Lecture Notes - Lecture 3: Thermal Expansion, Sign Convention

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9 Oct 2019
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PHY1321 LECTURE 3
Heat Capacity
The heat capacity, C, of a sample is defined as the amount of energy needed to raise the
temperature of that sample by 1oC.
If energy Q produces a change of temperature of DT, then Q = C DT.
Specific Heat
Specific heat, c, is the heat capacity per unit mass.
If energy Q transfers to a sample of a substance of mass m and the temperature changes
by DT, then the specific heat is
The specific heat is essentially a measure of how thermally insensitive a substance is to
The greater the substance’s specific heat, the more energy that must be added to a
given mass to cause a temperature change.
The equation is often written in terms of Q : Q = m c DT
Internal Energy Revisited
The change in internal energy of a system can be identified with m c Δ t.
If we ignore any thermal expansion or contraction of the system.
Then ΔEint = Q
The internal energy of a system can be changed by transferring energy into the system
by any mechanism.
This also indicates temperature is related to the energy of the molecules of a system.
Specific Heat of Water
Water has the highest specific heat of common materials.
This is in part responsible for many weather phenomena:
Moderate climates near large bodies of water
Global wind systems
land and sea breezes
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