Which quantity measures the opposition to the flow of current in a material?

• A. Resistance
• B. Voltage
• C. Impedance
• D. Capacitance

Answer: (A)

The main concept here is how a material resists the flow of electric current. That opposition is described by resistance, which is the proportionality between voltage and current in a conductor (Ohm’s law: V = IR). Resistance depends on the material’s resistivity, its length, and its cross-sectional area, and it typically increases with temperature for metals. In alternating current situations, the total opposition to current is called impedance, which adds reactive effects from capacitance and inductance to the basic resistance, but the fundamental measure of how much a material resists steady current flow is resistance. Voltage is the driving force that pushes charge, while capacitance relates to stored charge in a capacitor, so they aren’t the measure of opposition itself.