Joule's First Law Formula |
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\( q \;=\; I^2 \cdot R \cdot t \) (Joule's First Law) \( I \;=\; \sqrt{ \dfrac{ q }{ R \cdot t } } \) \( R \;=\; \dfrac{ q }{ I^2 \cdot t }\) \( t \;=\; \dfrac{ q }{ I^2 \cdot R} \) |
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| Symbol | English | Metric |
| \( q \) = Heat | \(Btu\;/\;lbm\) | \(kJ\;/\;kg\) |
| \( I \) = Current | \(A\) | \(C\;/\;s\) |
| \( R \) = Resistance | \(\Omega\) | \(kg-m^2\;/\;s^3-A^2\) |
| \( t \) = Time Duration | \(sec\) | \(s\) |
Joule's laws refer to several principles in physics, particularly in the realm of thermodynamics and electricity. These laws have been instrumental in understanding and formulating various principles in physics, particularly in the study of energy conversion and thermodynamics. There are generally two key laws attributed to Joule, though they are often discussed in different contexts. Joule’s first law is more commonly referenced in electrical engineering, while Joule’s second law is significant in thermodynamics.
Joule's First Law (Joule Heating or Joule Effect) - The heat generated in a conductor is directly proportional to the square of the electric current flowing through it, the resistance of the conductor, and the time for which the current flows.
Joule's Second Law Formula |
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\( \Delta U \;=\; n \cdot C_v \cdot \Delta T \) (Joule's Second Law) \( n \;=\; \dfrac{ \Delta U }{ C_v \cdot \Delta T }\) \( C_v \;=\; \dfrac{ \Delta U }{ n \cdot \Delta T }\) \( \Delta T \;=\; \dfrac{ \Delta U }{ n \cdot C_v }\) |
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| Symbol | English | Metric |
| \( \Delta U \) = Internal Energy Change | \(Btu\) | \(J\) |
| \( n \) = Number of Moles | \(dimensionless\) | \(dimensionless\) |
| \( C_v \) = Mole Specific Heat Capacity at Constant Volume | \(ft^3\) | \(m^3\) |
| \( \Delta T \) = Temperature Change | \(F\) | \(K\) |
Joule's Second Law (Related to Thermodynamics and Work) -The internal energy of an ideal gas is a function of temperature alone and is independent of its volume or pressure. This is tied to Joule's experiments on the mechanical equivalent of heat. 