---
title: "Short Circuit — AP Physics 2 Definition & Exam Guide"
description: "A short circuit is a low-resistance path where charge flows with no potential difference change. Learn how it reroutes current and shows up on AP Physics 2."
canonical: "https://fiveable.me/ap-physics-2-revised/key-terms/short-circuit"
type: "key-term"
subject: "AP Physics 2"
unit: "Unit 11"
---

# Short Circuit — AP Physics 2 Definition & Exam Guide

## Definition

In AP Physics 2, a short circuit is a circuit (or path within a circuit) in which charges can flow with no change in potential difference, usually because a low-resistance wire bypasses circuit elements, so nearly all the current takes that path instead.

## What It Is

A short circuit happens when charges can flow through a path with essentially zero change in [potential difference](/ap-physics-2-revised/key-terms/electric-potential-difference "fv-autolink"). In practice, that means a plain wire (which is nearly resistance-free) connects two points that should have [circuit elements](/ap-physics-2-revised/unit-11/2-simple-circuits/study-guide/LROjr9EJ6hjfPDMC "fv-autolink") between them. Since the wire offers almost no resistance, current floods through it and skips whatever it bypasses. The bypassed element still sits in the circuit physically, but electrically it might as well not exist.

Here's the intuitive picture. Current is lazy. Give it a free, zero-resistance shortcut and it takes the shortcut. If a wire is accidentally connected across a [resistor](/ap-physics-2-revised/key-terms/resistor "fv-autolink"), both ends of that resistor end up at the same potential, so no current bothers going through the resistor anymore. The total resistance of the circuit drops, which by Ohm's law means the battery pushes out a much larger current. That spike in current is exactly why real-world short circuits melt wires and trip breakers.

## Why It Matters

Short circuits live in Topic 11.2 (Simple Circuits) in [Unit 11](/ap-physics-2-revised/unit-11 "fv-autolink"): Electric Circuits, under learning objective 11.2.A, which asks you to describe the behavior of a circuit. The essential knowledge spells out three circuit states you need to keep straight. A closed circuit lets charge flow, an [open circuit](/ap-physics-2-revised/key-terms/open-circuit "fv-autolink") blocks charge flow, and a short circuit lets charge flow with no change in potential difference. The exam loves testing whether you can predict what happens to current, voltage readings, and brightness of bulbs when a wire accidentally bridges part of a circuit. Shorting an element changes the equivalent resistance of the whole circuit, so this concept connects directly to Ohm's law, series and parallel analysis, and Kirchhoff's rules. If you can't spot a short on a schematic, you'll misanalyze the entire circuit.

## Connections

### [Open circuit (Unit 11)](/ap-physics-2-revised/key-terms/open-circuit)

These are opposites in a useful way. An open circuit has a break, so [current](/ap-physics-2-revised/unit-11/1-electric-current/study-guide/QaFR8etPqRmh5pdg "fv-autolink") is zero everywhere in that loop. A short circuit has a free path, so current gets huge. One kills the current, the other lets it run wild.

### [Series resistors (Unit 11)](/ap-physics-2-revised/key-terms/series-resistors)

Shorting one resistor in a series chain removes its [resistance](/ap-physics-2-revised/unit-11/3-resistance-resistivity-and-ohms-law/study-guide/y0ZmKqhOPqeLWZFa "fv-autolink") from the total. The equivalent resistance drops, so the current through the remaining resistors goes up. This is the classic 'one bulb gets brighter when another is shorted' question.

### Capacitors in circuits (Unit 11)

An uncharged capacitor acts like a short circuit at the instant a switch closes, because there's no potential difference across it yet. Current flows through its branch as if it were bare wire. Once [fully charged](/ap-physics-2-revised/unit-11/8-resistor-capacitor-rc-circuits/study-guide/Bzx859T2I32htsAl "fv-autolink"), it flips and acts like an open circuit instead.

### Power dissipation and Ohm's law (Unit 11)

A short slashes resistance, so current spikes, and power dissipated in the wires (P = I²R) spikes with it. That's the physics behind why household shorts cause overheating and fires, a scenario AP questions use for real-world framing.

## On the AP Exam

Short circuits show up mostly in multiple-choice scenarios where a wire accidentally bridges part of a circuit and you have to predict the result. Typical stems include a household circuit where the hot wire touches the neutral wire (and you explain why the resulting current surge is dangerous), or a student's circuit where a stray wire bypasses two of three parallel resistors (and you reason about what happens to current and power). You should also recognize the capacitor case, where an uncharged capacitor momentarily behaves like a short right after a switch closes. Watch for trick questions too. If an ammeter reading suddenly drops to zero, that's an open circuit, not a short. A short would make the reading jump up. No released FRQ has used 'short circuit' verbatim, but circuit-analysis FRQs routinely reward students who can redraw a schematic with a shorted element removed and recompute equivalent resistance.

## short circuit vs Open circuit

An open circuit has a gap, so charges cannot flow at all and current is zero. A short circuit is the opposite problem. Charges flow too easily through a near-zero-resistance path with no change in potential difference, so current becomes very large. Quick check on the exam: ammeter reads zero means open; ammeter spikes (or a fuse blows) means short.

## Key Takeaways

- A short circuit is a path where charges flow with no change in potential difference, usually a low-resistance wire bypassing circuit elements.
- When an element is shorted, both of its terminals sit at the same potential, so essentially no current flows through that element.
- Shorting part of a circuit lowers the total equivalent resistance, which makes the current from the battery increase, sometimes dangerously.
- A short circuit and an open circuit are opposites. An open circuit stops current completely, while a short circuit lets current surge.
- An uncharged capacitor behaves like a short circuit at the moment a switch closes, then like an open circuit once it's fully charged.
- On the exam, redraw the schematic treating a shorted element as if it were replaced by a plain wire, then analyze the simpler circuit.

## FAQs

### What is a short circuit in AP Physics 2?

It's a circuit in which charges can flow with no change in potential difference, typically because a low-resistance wire bypasses one or more circuit elements. This definition comes straight from the essential knowledge under learning objective 11.2.A in Unit 11.

### Does a short circuit mean no current flows?

No, it's the opposite. A short circuit lets a very large current flow because the resistance along the shortcut path is nearly zero. Zero current describes an open circuit, where the loop is physically broken.

### How is a short circuit different from an open circuit?

An open circuit has a gap, so no charge flows and an ammeter reads zero. A short circuit has a zero-resistance bypass, so current jumps to a large value. If an exam question says the ammeter suddenly reads zero, the answer is an open circuit, not a short.

### What happens to a resistor when it gets shorted out?

A wire connects its two terminals, so both ends are at the same potential and almost no current flows through the resistor itself. The circuit's equivalent resistance drops, so current through the rest of the circuit increases. In a series chain, the other resistors get more current and dissipate more power.

### Why are short circuits dangerous in real life?

When a hot wire touches a neutral wire, the resistance between them is nearly zero, so the current surges far above normal levels. That huge current dissipates a lot of power as heat in the wiring (P = I²R), which can melt insulation and start fires. Fuses and circuit breakers exist to cut the circuit before that happens.

## Related Study Guides

- [11.2 Simple Circuits](/ap-physics-2-revised/unit-11/2-simple-circuits/study-guide/LROjr9EJ6hjfPDMC)

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