Resistance is defined as what?

• A. Opposition to current flow, measured in ohms (Ω)
• B. A measure of voltage drop
• C. A unit of power
• D. A measure of charge

Answer: (A)

Resistance is the opposition to the flow of electric current. It comes from how electrons collide with atoms in a conductor and depends on the material, its geometry (length and cross-sectional area), and temperature. Ohm's law ties it all together: V = I R, so resistance is the ratio of voltage to current (R = V / I). The unit is the ohm (Ω). In practice, a resistor limits current and converts part of the electrical energy into heat, with power described by P = I^2 R = V^2 / R. The other descriptors refer to voltage drop (voltage), the unit of power (watt), and the amount of electric charge (coulombs).