Basic Study Material Physics for JEE

Units of Energy

The SI unit of energy is joule (J)

1 joule (J) = 1 newton metre (N m)

                 = 1 watt second (W s)

Large units of energy are 

1 kilo watt hour (kWh) = 1000 W × 1 h

                                      = 1000 W × 3600 s

                                      = 3.6 × 10⁶ W s

                                      = 3.6 × 10⁶ J

1 mega watt hour (MWh) = 3.6 × 10⁹ J

 Smallest unit of energy is electron volt (eV)

1 electron volt (eV) = 1.6 × 10⁻¹⁹ J

1 kilo electron volt (keV) = 1.6 × 10⁻¹⁶ J

1 mega electron volt (MeV) = 1.6 × 10⁻¹³ J

The energy of subatomic particles like electrons, protons, neutrons etc are measured in eV, keV, MeV etc.,

Another such unit is rydberg

1 rydberg = 13. 6 eV

In SI, all forms of energy are measured in joule (J). In CGS system, mechanical energy is measured is erg while heat energy is measured in calorie (cal)

1 cal = 4. 18 J