A curved mirror is a mirror with a curved reflective surface, which may be either convex (bulging outward) or concave (bulging inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors.

Convex mirror

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A convex mirror, or diverging mirror, is a curved mirror in which the reflective surface bulges toward the light source. Such mirrors always form a virtual image, since the focus F and the center of curvature 2F are both imaginary points "inside" the mirror, which cannot be reached.

A collimated (parallel) beam of light diverges (spreads out) after reflection from a convex mirror, since the normal to the surface differs with each spot on the mirror.

Image

The image is always virtual, smaller, and upright. These features make convex mirrors very useful: since they make everything appear smaller, they can cover a wider field of view than a normal flat mirror would, since the image is "compressed". The passenger-side mirror on a car is typically a convex mirror. In some countries, these are labeled with the safety warning "Objects in mirror are closer than they appear", to warn the driver of the convex mirror's distorting effects on distance perception.

Concave mirrors

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A concave mirror, or converging mirror, has a reflecting surface that bulges inward (away from the incident light). Unlike convex mirrors, concave mirrors show different types of image depending on the distance between the object and the mirror itself.

These mirrors are called "converging" because they tend to collect light that falls on them, refocusing parallel incoming rays toward a focus. This is because the light is reflected at different angles, since the normal to the surface differs with each spot on the mirror.

Image

Note: S here stands for distance between object and mirror.

• When
  • Virtual
  • Upright
  • Magnified (larger)

• When $S=F$, no image is created.

• When , the image is:
  • Virtual
  • Inverted (vertically)
  • Magnified (larger)

• When $S=2F$, the image is:
  • Real
  • Inverted
  • Same size

• When $S>2F$, the image is:
  • Real
  • Inverted
  • Smaller

Mirror shape

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Most curved mirrors have a spherical profile. These are the simplest to make, and it is the best shape for general-purpose use. Spherical mirrors, however, suffer from spherical aberration. Parallel rays reflected from such mirrors do not focus to a single point. For parallel rays, such as those coming from a very distant object, a parabolic reflector can do a better job. Such a mirror can focus incoming parallel rays to a much smaller spot than a spherical mirror can.

Mirrors