Electric current is the fundamental SI electrical dimension, with the ampere (A) as its unit. Determine units for the following quantities as combinations of fundamental SI units.

Question

(a) Electric power
(b) Electric charge
(c) Electric potential difference
(d) Electric resistance
(e) Electric capacitance

Answer 1

There are many possible ways to deduce this, but perhaps the most straightforward is to write Newton’s law as and see what numerical value and units are required to make it work out. If one poundal is the force

required to accelerate then Newton’s law in these units is: 1 poundal So, in these

units,



a. Power is power, whether it is electrical, mechanical, or otherwise. Thus, electric power has the usual units of power:





b. Electric current is by definition the time rate of transfer of electrical charge. Thus



or charge = current*time = A s



c. Since power is given by the product of current and electric potential,



or



d. Because (by Ohm’s Law) current is electric potential divided by resistance,

or

(this is defined as the ohm)



e. Since electric potential is electric charge divided by electric capacitance,



or