{
  "schemaVersion": "1.0",
  "id": "https://elect-learn.org/en/lesson/04-voltage-current-power/",
  "url": "https://elect-learn.org/en/lesson/04-voltage-current-power/",
  "markdownUrl": "https://elect-learn.org/en/lesson/04-voltage-current-power/index.md",
  "jsonUrl": "https://elect-learn.org/en/lesson/04-voltage-current-power/index.json",
  "language": "en",
  "title": "Voltage, Current, Resistance, and Power",
  "description": "Turn formulas into intuition: voltage pushes, current flows, resistance limits, and power becomes heat or work.",
  "kind": "lesson",
  "safetyNotice": "Learning reference only: electrical codes, permits, inspection bodies, and licensing rules differ by region. This course is not a substitute for local code, licensed training, permits, or authority requirements. Before any hands-on work, de-energize, verify absence of voltage, and follow local regulators/AHJ and employer procedures.",
  "sections": [
    {
      "id": "ohms-law-tool",
      "heading": "Practise the relationships with two known values",
      "paragraphs": [
        "Use the free calculator for ideal positive-value DC resistive exercises, then explain which two values were entered and which two were derived."
      ],
      "links": [
        {
          "title": "Open the Ohm's law calculator",
          "url": "https://elect-learn.org/en/tools/ohms-law-calculator/"
        }
      ]
    },
    {
      "id": "section-1",
      "heading": "Lesson information",
      "paragraphs": [
        "Circuit Fundamentals · Basic · 20 min",
        "Circuits",
        "Interactive"
      ]
    },
    {
      "id": "section-2",
      "heading": "Voltage drives. Resistance limits. Power tells the rate.",
      "paragraphs": [
        "The source provides voltage. Closing the switch completes the path so current can flow through the load."
      ],
      "items": [
        "At fixed voltage, more resistance means less current.",
        "For an ideal resistive load: I = U ÷ R.",
        "Power P = U × I; the values below share one model."
      ]
    },
    {
      "id": "section-3",
      "heading": "Goals",
      "items": [
        "Use V=I×R and P=V×I to explain loads.",
        "Understand why current and heating are tightly related.",
        "Connect meter readings with circuit state."
      ]
    },
    {
      "id": "section-4",
      "heading": "Too many heaters on one power strip",
      "paragraphs": [
        "In winter, two heaters and a computer share one power strip, and the plug feels hot.",
        "Wrong call: Assuming it is safe because the breaker has not tripped.",
        "Stop point: Stop use and de-energize immediately if there is heat, odor, or discoloration.",
        "Reasoning path: Calculate total power/current and check circuit rating, power strip rating, and duration.",
        "Review: Common exam topics: Ohm's law, power, current, and conductor/equipment ratings."
      ]
    },
    {
      "id": "section-5",
      "heading": "Core concepts",
      "items": [
        "Voltage is the pushing difference; current is what actually flows through the load.",
        "More power means more energy per unit time, so heating matters.",
        "A load is not abstract; it is a lamp, heater, motor, or charger."
      ]
    },
    {
      "id": "tool-multimeter",
      "heading": "Digital Multimeter",
      "paragraphs": [
        "Measures voltage, continuity, and resistance so you verify instead of guess.",
        "Misuse and limits: Wrong jack or mode selection can damage the meter or create danger."
      ]
    },
    {
      "id": "tool-cable",
      "heading": "NM Cable / Conductors",
      "paragraphs": [
        "Carries circuit current; color and markings help identify use.",
        "Misuse and limits: Wrong gauge, jacket, environment, or color use may violate code."
      ]
    },
    {
      "id": "section-8",
      "heading": "Common Pitfalls",
      "items": [
        "Looking only at voltage and ignoring load current.",
        "Treating a power strip as a way to increase circuit capacity.",
        "Ignoring continuous loads and heat dissipation."
      ]
    },
    {
      "id": "section-9",
      "heading": "Safe Workflow",
      "items": [
        "List wattage or amperage for every load.",
        "Estimate current with P=V×I.",
        "Compare with device, strip, and circuit ratings; stop if heating appears."
      ],
      "ordered": true
    },
    {
      "id": "quiz-1",
      "heading": "At 120V, about how much current does a 1500W heater draw?",
      "paragraphs": [
        "About 12.5A because I=P/V=1500/120."
      ]
    },
    {
      "id": "quiz-2",
      "heading": "If a plug feels hot, should you keep watching it?",
      "paragraphs": [
        "No. Stop use, de-energize, and investigate ratings, connections, and load."
      ]
    },
    {
      "id": "section-12",
      "heading": "Look Back",
      "links": [
        {
          "title": "Review Lesson 3: voltage is measured across two points.",
          "url": "https://elect-learn.org/en/lesson/03-multimeter-basics/"
        }
      ]
    }
  ],
  "dateModified": "2026-10-23",
  "publisher": {
    "name": "Elect Learn",
    "url": "https://elect-learn.org"
  },
  "review": {
    "status": "not-independently-reviewed",
    "statement": "No independent professional review is recorded. Cited sources do not imply review or endorsement by those organizations.",
    "policyUrl": "https://elect-learn.org/en/methodology/"
  }
}