--- title: "Open, closed and short circuit" subject: "Basic Electrical Engineering" chapter: 1 key: "semester_1/basic_electrical_engineering:open-short-closed-circuit" source: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/open-short-closed-circuit site: BCT Engineering --- # Open, closed and short circuit Basic Electrical Engineering · Chapter 1: General Electric System - Asked in: 2073 Chaitra, 4 marks - Video: [Open Circuits, Closed Circuits & Short Circuits - Basic Introduction](https://www.youtube.com/watch?v=v5RJf_V0LYA) — The Organic Chemistry Tutor - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/open-short-closed-circuit - Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_engineering/chapter-1 ## Question Describe the open circuit, close circuit and short circuit with diagram. ## Short answer A closed circuit has a complete path, current flows, load gets voltage. An open circuit has infinite resistance, zero current, full voltage across the break. A short circuit has near-zero resistance, causing very high current and zero voltage across the short. ## Answer #### Closed circuit A closed circuit is a complete conducting path from the source, through the load and back to the source. Current flows. For a source *E* and load *R*, I = E/R, and the load gets its normal voltage. #### Open circuit An open circuit has a break in the path (an open switch or a broken wire). The resistance is infinite, so the current is zero and there is no voltage drop across the load. The full source voltage appears across the break (the open-circuit voltage). #### Short circuit A short circuit is a path of almost zero resistance across the source or load. The current becomes very large, I = E/R_internal, which can burn the wires and damage the source. The voltage across the shorted part is zero. Fuses and circuit breakers protect against it. ```text Closed Open Short +--[sw]--+ +--/ --+ +--[sw]--+------+ | | | | | | | (E) [R] (E) [R] (E) [R] wire | | | | | | | +--------+ +------+ +--------+------+ I = E/R I = 0 I very large ``` | Condition | Resistance | Current | Load voltage | |---|---|---|---| | Closed | finite R | E/R | E | | Open | ∞ | 0 | 0 | | Short | ≈ 0 | very large | 0 | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In a closed circuit with source E and load R, what are the current and load voltage? A. I = 0, load voltage 0 B. I = E/R, load gets its normal voltage C. I very large, load voltage 0 D. I = E/R, load voltage 0 Answer: B. A complete path lets current I = E/R flow and the load receives the normal voltage. (Key point: Closed circuit) 2. In an open circuit, which statement is correct? A. Current is very large and voltage across the load is E B. Current is E/R and the break has zero voltage C. Resistance is infinite, current is zero and the full source voltage appears across the break D. Resistance is zero and current is zero Answer: C. A break has infinite resistance, so no current flows and the open-circuit voltage appears across the gap. (Key point: Open circuit) 3. Why is a short circuit dangerous? A. Resistance is infinite so voltage becomes too high B. Current is zero so the source overheats C. The load voltage doubles D. Resistance is almost zero so current I = E/R_internal becomes very large and can burn wires and the source Answer: D. A near-zero resistance path limits current only by the source internal resistance, causing a huge current; fuses and breakers protect against it. 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