A real image is an image formed where light rays actually converge after refracting through a lens or reflecting off a mirror. In AP Physics 2, real images have a positive image distance in the lens/mirror equation, are inverted relative to the object, and can be projected onto a screen.
A real image is what you get when light rays physically meet at a point after passing through a lens or bouncing off a mirror. Because actual light arrives at that location, you can put a screen there and see the image on it. That's the practical test. A projector throws a real image onto a wall; your eye's lens forms a real image on your retina.
In AP Physics 2, real images come from converging optics, meaning convex (converging) lenses and concave mirrors, when the object sits outside the focal point. The math backs this up. In the lens/mirror equation (1/f = 1/s_o + 1/s_i), a real image has a positive image distance s_i. That positive sign then makes the magnification (m = -s_i/s_o) negative, which tells you the image is inverted. Ray diagrams show the same story visually, with the refracted or reflected rays themselves crossing at the image location instead of just appearing to come from a point behind the optic.
Real images live in the geometric optics unit of AP Physics 2 (Unit 13), where you're expected to predict image characteristics (real vs. virtual, upright vs. inverted, magnified vs. reduced) for lenses and mirrors using both ray diagrams and the lens/mirror equation. The whole unit hinges on connecting three representations of the same situation: the ray diagram, the equation with correct signs, and a verbal description of the image. "Real" is one of the three characteristics you're asked about constantly, and it's the one that links directly to a sign convention (s_i > 0). If you can correctly classify an image as real, you've usually nailed the other two characteristics for free, since real images from a single lens or mirror are always inverted.
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Virtual image (Unit 13)
Virtual images are the flip side. No light actually passes through a virtual image, so it can't be projected, its image distance is negative, and it's upright. Every image-classification question on the exam is really asking you to pick between these two.
Lens/mirror equation (Unit 13)
This equation is how you prove an image is real without drawing anything. Solve 1/f = 1/s_o + 1/s_i, and a positive s_i means real. The physics fact (rays actually converge) and the math fact (s_i > 0) are the same statement in two languages.
Magnification (Unit 13)
Since m = -s_i/s_o, a real image (positive s_i) automatically gives negative magnification, which means inverted. That's why a single converging lens never makes a real, upright image. The signs won't allow it.
Focal point (Unit 13)
The focal point is the dividing line. With a converging lens or concave mirror, an object outside the focal point gives a real image, while an object inside it gives a virtual one. That's why a magnifying glass (object inside f) shows an upright virtual image, but the same lens projects an inverted real image of a distant window.
Multiple-choice questions typically give you an object, a lens or mirror, and a focal length, then ask you to classify the image as real or virtual, inverted or upright, and larger or smaller. You should be able to answer two ways: by sketching a quick ray diagram (real image = the rays themselves cross) and by checking the sign of s_i from the lens/mirror equation. Free-response questions in optics often hand you a ray diagram to complete or ask you to justify why an image can or cannot be projected onto a screen. The winning justification is always the same idea, that light actually converges at a real image's location, so a screen placed there catches the light. Watch for trap setups like an object inside the focal length of a converging lens, which flips the answer to virtual.
Both are images, but only a real image is made of light that actually arrives at a location. A real image forms where rays truly intersect, has positive image distance, is inverted, and can be projected on a screen. A virtual image forms where rays only appear to come from (your brain traces them backward), has negative image distance, is upright, and cannot be caught on a screen. Quick check: if you could hold up paper and see the image on it, it's real. Your bathroom mirror image is virtual, which is why there's no tiny you floating behind the glass that a screen could capture.
A real image forms where light rays actually intersect after refraction or reflection, so it can be projected onto a screen.
In the lens/mirror equation, a real image always has a positive image distance (s_i > 0).
Real images from a single lens or mirror are always inverted, which shows up as a negative magnification (m = -s_i/s_o).
Only converging optics (convex lenses and concave mirrors) can form real images, and only when the object is outside the focal point.
Diverging lenses and convex mirrors never form real images of real objects, no matter where the object is placed.
On a ray diagram, a real image is where the drawn rays themselves cross, not where their backward extensions meet.
A real image is an image formed where light rays actually converge after passing through a lens or reflecting off a mirror. Because real light arrives there, it can be projected onto a screen, and in the lens/mirror equation it has a positive image distance.
Not from a single lens or mirror. A real image always has positive s_i, which forces the magnification m = -s_i/s_o to be negative, meaning inverted. You'd need a second optical element (like a two-lens system) to flip a real image back upright.
A real image is formed by rays that actually meet and can be projected on a screen; a virtual image is formed where rays only appear to originate and cannot be projected. Mathematically, real images have positive image distance and virtual images have negative image distance.
Yes, as long as the object sits outside the focal point. A convex (converging) lens then bends rays so they cross on the far side, creating an inverted real image. Move the object inside the focal point and the same lens produces an upright virtual image instead, which is how a magnifying glass works.
No. A plane mirror only makes virtual images, because the reflected rays diverge and never actually cross. The image you see appears to be behind the mirror, where no light actually goes. Only concave mirrors (and converging lenses) can form real images of real objects.
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