Which formula expresses resistance R when voltage E and current I are known?

• A. E = I / R
• B. R = E / I
• C. I = E / R
• D. V = I R

Answer: (B)

Ohm’s law ties voltage, current, and resistance together. It says E = I R. To get resistance as a function of the known quantities, isolate R by dividing both sides by I. That gives R = E / I. This form directly expresses resistance using the voltage and current you have, and the units come out as ohms (volts per ampere). Other forms either describe a different quantity (like current) or use a different voltage symbol and would require reworking to present R explicitly as E divided by I, so the direct expression for R is E divided by I.