---
title: "Image — AP Physics 2 Definition & Exam Guide"
description: "In AP Physics 2, an image is the optical reproduction of an object formed by a mirror or lens, described by its position, size, orientation, and real/virtual type."
canonical: "https://fiveable.me/ap-physics-2-revised/key-terms/image"
type: "key-term"
subject: "AP Physics 2"
unit: "Unit 13"
---

# Image — AP Physics 2 Definition & Exam Guide

## Definition

In AP Physics 2, an image is the optical reproduction of an object formed when light rays reflect off a mirror or refract through a lens, fully described by four properties: position (where it forms), size (magnification), orientation (upright or inverted), and type (real or virtual).

## What It Is

An image is what you get when light rays leaving an object get redirected by a mirror or [lens](/ap-physics-2-revised/key-terms/lens "fv-autolink") and either actually converge somewhere (a **[real image](/ap-physics-2-revised/key-terms/real-image "fv-autolink")**) or merely appear to come from somewhere (a **virtual image**). On the AP exam, "describe the image" is shorthand for nailing four specific properties: where it is, how big it is, whether it's upright or inverted, and whether it's real or virtual.

The physics behind image formation comes down to focal points. Per learning objective 13.2.A, rays parallel to the principal axis of a concave (converging) mirror reflect through a common focal point in front of the mirror. The same rays hitting a convex (diverging) mirror reflect so they *appear* to come from a focal point behind the mirror. A plane mirror's focal point sits at infinity, which is why it always gives you an upright, same-size virtual image. For spherical mirrors, the focal point sits halfway between the mirror's surface and its [center of curvature](/ap-physics-2-revised/unit-13/2-images-formed-by-mirrors/study-guide/INg7VTuspNL1m0MQ "fv-autolink"), so focal length is half the radius of curvature. Where the object sits relative to that focal point determines everything about the image.

## Why It Matters

Image is the central deliverable of [Unit 13](/ap-physics-2-revised/unit-13 "fv-autolink") (Geometric Optics). Learning objective 13.2.A asks you to describe the image formed by a mirror, and the parallel skill for lenses runs through the rest of the unit. Every [ray diagram](/ap-physics-2-revised/key-terms/ray-diagram "fv-autolink") you draw, every mirror equation you solve, and every magnification you calculate exists to answer one question, which is "what does the image look like and where is it?" If you can confidently classify an image as real or virtual, upright or inverted, enlarged or reduced, you've mastered the core of geometric optics. The sign conventions in the mirror and lens equations (positive vs. negative image distance, positive vs. negative magnification) are just the algebraic encoding of those same image properties.

## Connections

### [Ray Diagram (Unit 13)](/ap-physics-2-revised/key-terms/ray-diagram)

A ray diagram is how you *find* an image without any algebra. Trace two [principal rays](/ap-physics-2-revised/key-terms/principal-rays "fv-autolink") from the tip of the object, and where they cross (or appear to cross) is where the image forms. Real images form where rays actually intersect; virtual images form where extended rays appear to intersect behind the mirror.

### [Magnification (Unit 13)](/ap-physics-2-revised/key-terms/magnification)

[Magnification](/ap-physics-2-revised/key-terms/magnification "fv-autolink") turns image description into a number. It compares image height to object height, and its sign tells you orientation. Positive magnification means upright (and virtual for a single mirror), while negative means inverted (and real). A practice question giving you an image 1/3 the object's height is handing you m = +1/3 in disguise.

### [Focal Length (Unit 13)](/ap-physics-2-revised/key-terms/focal-length)

[Focal length](/ap-physics-2-revised/key-terms/focal-length "fv-autolink") is the single number that controls what kind of image a curved mirror can make. Objects beyond the focal point of a concave mirror produce real, inverted images; objects inside it produce virtual, upright, enlarged ones. Convex mirrors have negative focal lengths and can only ever produce small, upright, virtual images.

### [Plane Mirror (Unit 13)](/ap-physics-2-revised/key-terms/plane-mirror)

The plane mirror is the simplest image-maker and the limiting case of a curved mirror. Its focal point sits at infinity, so the image is always virtual, upright, the same size as the object, and exactly as far behind the mirror as the object is in front. It's the baseline you compare every curved-mirror image against.

## On the AP Exam

Multiple-choice questions hand you two of the three quantities in the mirror equation and ask for the third, but the trap is always sign conventions. A virtual image "12 cm behind the mirror" means the image distance is negative 12 cm, and getting the focal length right depends on that sign. Other MCQ stems test conceptual classification, like recognizing that a convex mirror producing an image 1/3 the object's height must give a virtual, upright image, or counting the multiple images formed by two plane mirrors set at an angle. On the free-response side, the 2017 Long FRQ had students design an experiment to determine the focal length of a convex lens using a light source, lens, and screen. The key insight is that only a real image can be projected onto a screen, so the experiment itself depends on understanding image type. Expect to draw ray diagrams, justify whether an image is real or virtual, and explain how moving the object changes the image.

## image vs real image vs. virtual image

A real image forms where light rays actually converge, so you can project it onto a screen. A virtual image forms where rays only *appear* to originate, so no light actually passes through that location and it can't be projected. The quick test on the exam is the sign of the image distance. Positive means real (in front of a mirror), negative means virtual (behind it). Concave mirrors can make either kind depending on object position, but convex and plane mirrors only ever make virtual images.

## Key Takeaways

- Describing an image on the AP exam means giving four properties: position, size, orientation (upright or inverted), and type (real or virtual).
- Real images form where reflected rays actually converge and can be projected on a screen; virtual images form where rays only appear to originate and cannot.
- Concave mirrors can form real, inverted images (object beyond the focal point) or virtual, upright, enlarged images (object inside the focal point).
- Convex mirrors and plane mirrors always form virtual, upright images, and a convex mirror's image is always smaller than the object.
- In the mirror equation, a virtual image has a negative image distance, and a convex mirror has a negative focal length, so watch your signs.
- The focal point of a spherical mirror sits halfway between the mirror's surface and its center of curvature, while a plane mirror's focal point is at infinity.

## FAQs

### What is an image in AP Physics 2?

An image is the optical reproduction of an object formed when a mirror reflects or a lens refracts light rays. On the exam you describe it by four properties: position, size, orientation, and whether it's real or virtual.

### Can a virtual image be projected onto a screen?

No. Only real images can be projected, because light rays actually converge at a real image's location. A virtual image is just where rays appear to come from, so no light actually arrives there. This is exactly why the 2017 FRQ's screen-based experiment only works with a real image.

### What's the difference between a real and a virtual image?

A real image forms where reflected or refracted rays physically intersect and has a positive image distance. A virtual image forms where extended rays appear to intersect (behind a mirror) and has a negative image distance. For a single mirror, real images are inverted and virtual images are upright.

### Do convex mirrors ever form real images?

No. A convex (diverging) mirror spreads parallel rays so they appear to come from a focal point behind the mirror, so it can only form virtual, upright, reduced images no matter where the object sits. That's why a question describing an image 1/3 the object's height behind a convex mirror is always virtual.

### Why does a plane mirror image look the same size as the object?

A plane mirror's focal point is at infinity, so it doesn't converge or diverge rays at all. The result is a virtual image the same size as the object, located exactly as far behind the mirror as the object is in front, with magnification of +1.

## Related Study Guides

- [13.2 Images Formed by Mirrors](/ap-physics-2-revised/unit-13/2-images-formed-by-mirrors/study-guide/INg7VTuspNL1m0MQ)

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