Voltage and Resistance

Learn the models, terms, and applications of voltage and resistance.

Lesson 2 of 32 parts Practice Flashcards

1/2

Ohm’s Law and Resistance

Objective: Use V = IR for an ohmic component within its operating range.

Electrical resistance is the ratio of potential difference across a component to current through it under stated conditions, R = V/I, measured in ohms (Ω = V/A). For an ohmic resistor at approximately constant temperature, V = IR. A 12 V drop across a 4 Ω resistor gives 3 A. Doubling voltage across the same ohmic resistor doubles current, while doubling resistance at fixed voltage halves it. Not every component is ohmic: filament lamps, diodes, and changing-temperature materials may have nonlinear V–I behavior. Resistance depends on material, geometry, and temperature. Apply the equation to a specific component or equivalent circuit, not to mismatched points and branches.

Worked examples

Try itA 12 V drop across a 4 Ω resistor gives what current?Show answer

1. Identify the relevant concept in this section. 2. I = V/R = 12/4 = 3 A. 3. Answer: 3 A

Swipe sideways to move between sections

Ohm’s Law and Resistance

Objective: Use V = IR for an ohmic component within its operating range.

Worked examples

Try itA 12 V drop across a 4 Ω resistor gives what current?Show answer

1. Identify the relevant concept in this section. 2. I = V/R = 12/4 = 3 A. 3. Answer: 3 A

Applications and Worked Problems

Objective: Apply voltage and resistance to calculations, evidence, and specified situations.

For an ohmic element under specified physical conditions, V=IR. Ohm’s law is not a universal rule for every device or temperature. Electrical power delivered to an element is P=IV; for the ohmic relation it can also be written I²R or V²/R. Resistance depends on material, dimensions, and conditions. Maintain a consistent component boundary when comparing voltages and currents, and use volts, amperes, and ohms in the calculations.

Formulas

$V=IR$
$P=IV$
P=I²R for an ohmic resistor

Worked examples

Try itAn ohmic resistor has R=3 Ω and V=8 V. Find current.Show answer

1. I=V/R. 2. 8/3=2.667 A.

Try itAn ohmic resistor carries 1 A with resistance 3 Ω. Find voltage.Show answer

1. V=IR. 2. 1×3=3 V.

You finished the reading!

Lock it in with a few practice questions, then move on to the next lesson.

Practice Next lesson

Previous lessonCharge and Current Next lessonSeries and Parallel Circuits