basic ohm's law

 

voltage is the pressure that pushes electron current against opposing resistance

1) If a 330 ohm resistor is connected to a 9V DC source what is the current that will flow?

In daily use an electrician is most likely going to use ohm's law/power to determine current in a circuit which will help determine the size of cable to be used in a circuit installation.
(other considerations such as number of conductors in the conduit, type of insulation, and length, determine the final cable sizing calculation)

2) This question uses power formula to determine the size of cable used to feed a commercial baker's oven.


bakersp18.jpg Bakers Pride Electric Counter
Top Pizza Oven P18
 

BP-P18S
$1,065.00
Single compartment, 3" deck height ovens feature two ceramic hearth baking decks and are designed for pizza, pretzels, flat breads and bakery products baked directly on the hearth deck, on screens, or on baking sheets. 120V not recommended for fresh dough pizza. Stainless exterior. These Pizza ovens are stackable. 17-1/2 x 17-3/4 inch deck size. 23"x25"x"27" overall dimensions. Available 120V-1800W or 208-240V-2850W. 300-650 degrees F. UL, NSF approved.
 
Voltage:

If you are energizing the above oven at 120V what size of cable would you use?

WIRE SIZE CALCULATOR

So a 14 AWG conductor could be used as the minimum size a size 12 would be safer but cost a little more.