Introduction:
Resistance is a fundamental property that impedes the flow of electric charge. In series circuits, understanding what resistance actually does clarifies how currents, voltages, and powers distribute across components, guiding both analysis and design choices.
Given Data / Assumptions:
- Steady DC source and lumped resistive elements.
- Resistive loads obey Ohm's law.
- No reactive components are present (ignoring capacitance and inductance).
Concept / Approach:
Ohm's law states V = I * R. For a given applied voltage, increasing resistance reduces current; equivalently, resistance opposes current flow. Power in a resistor is P = I^2 * R or P = V^2 / R, reflecting that resistance converts electrical energy into heat proportional to current or voltage squared.
Step-by-Step Solution:
Start with V = I * R. Hold V constant; as R increases, I decreases.Interpretation: resistance presents opposition to charge movement through collisions and lattice interactions.Any series resistor develops a voltage drop: V_drop = I * R, demonstrating the opposing effect.Energy perspective: electrical energy is dissipated as heat due to this opposition, quantified by P = I^2 * R.
Verification / Alternative check:
Measurements across a variable resistor (rheostat) on a fixed-voltage supply show current decreasing as resistance increases, directly verifying resistance as opposition to current flow.
Why Other Options Are Wrong:
- control the voltage: Source sets voltage; resistors divide it but do not control the source value.
- double the current: Only occurs if R halves (with voltage fixed), not a general property.
- halve the power: Power depends on both I and R; no universal halving occurs.
- eliminate voltage drop: Resistors necessarily create voltage drops; eliminating drop contradicts V = I * R.
Common Pitfalls:
- Assuming resistors 'consume' current; they oppose current and dissipate power but current is the same through all series elements.
- Confusing voltage control with voltage division; the latter is a byproduct of opposing current.
Final Answer:
oppose current
Discussion & Comments