Kàttanug mbëj xeetu kàttan la gu lonku ci doole walla tool yu jóge ci mbëj, maanaam lu ñeel yëngug, walla doxub, yani mbëj. Kàttanu mbëj manees na koo jëfandikoo ngir defi liggéey, leeral, tàngal,... Kàttanu mbëj manees na koo natt ci dawaanu mbëj bi, balaa dara manees naa xayma liggéey bi W = Q ⋅ Δ V {\displaystyle W=Q\cdot \Delta V} , Liggéey bi W ciy joule, yan bi Q ciy coulomb ak wuuteeg aj gi Δ V {\displaystyle \Delta V} ciy volt. ak Q = I ⋅ t {\displaystyle Q=I\cdot t} , I dawaanu mbëj bi, t jamono ji: W = Δ V ⋅ I ⋅ t = P ⋅ t {\displaystyle W=\Delta V\cdot I\cdot t=P\cdot t} , te P {\displaystyle P} di Ngóora ciy watt.