Which formula gives resistance?

• A. R = V / I
• B. V = I R
• C. I = V / R
• D. P = I^2 R

Answer: (A)

Resistance tells us how much a component opposes the flow of current. Ohm’s law defines this opposition as the ratio of voltage to current: R = V / I. This form directly gives the value of resistance.

The other expressions are related but not as direct. V = IR is the same idea written differently—voltage equals current times resistance—so it’s equivalent but doesn’t present R by itself. I = V / R gives current in terms of voltage and resistance, not the resistance itself. P = I^2 R involves power, not resistance, even though it includes R.