Joule

The joule (symbol: J) ( or sometimes ) is a unit in the SI system named after English physicist James Prescott Joule.

Classical mechanics

Electromagnetism
Electronics
1 J is defined as the work done for one ampere of electric current to pass through an electric circuit with external resistance equivalent to one ohm per second. It can be illustrated by the following equations:

E = C V — (1)V = I R — (2)P = V I — (3)E = P t — (4)Combining (2), (3) and (4),E = I2 R t

where V is the voltage, E is the electrical energy, C is the charge, I is the current, R is the resistance, P is the power and t is the time of energy transfer.

Atomic physics
Arithmetically, 1 J ≈ 6.24 × 1012 MeV due to mass-energy equivalence. One unified atomic mass unit (u, amu or Da) is approximatey 931 MeV of energy (M = 106).

Derivation1 amu ≈ 1.66 × 10-27 kg (¹⁄₁₂ mass of a carbon-12 isotope by definition). Speed of light (c) = 3.00 × 108 ms-1.
ΔE = Δmc2ΔE = (1.66 × 10-27)(3.00 × 108)2= 1.49 × 10-10 J∵ 1 eV ≈ 1.60 × 10-19 J1 MeV = 1.60 × 10-19 × 106 J= 1.60 × 10-13 J1.49 × 10-10 J =  MeV = 931 MeV (3 s.f.)

∴ 1 amu ≈ 931 MeV

Related pages
Energy

References

Category:SI derived units
Category:Units of energy
Category:Biology
Category:Chemistry