Glossary
Center of Curvature (C)
For a spherical mirror, it is the center of the imaginary sphere from which the mirror's surface is a part.
Example:
If you imagine completing the sphere of a curved mirror, the Center of Curvature (C) would be at its very middle.
Concave Mirrors
Spherical mirrors with a reflective surface that curves inward, capable of forming both real and virtual images depending on object placement.
Example:
A satellite dish acts like a large concave mirror, focusing incoming radio waves to a single point.
Converging (Convex) Lenses
Lenses that are thicker in the middle and cause parallel light rays to converge to a single focal point on the opposite side.
Example:
A magnifying glass is a Converging (Convex) Lens that can focus sunlight to a point.
Convex Mirrors
Spherical mirrors with a reflective surface that curves outward, always producing virtual, upright, and reduced images.
Example:
The passenger-side mirror on a car is often a convex mirror, providing a wider field of view but making objects appear farther away.
Diverging (Concave) Lenses
Lenses that are thinner in the middle and cause parallel light rays to spread out as if originating from a single focal point on the same side.
Example:
The peephole in a door often uses a Diverging (Concave) Lens to provide a wide-angle, reduced view of the outside.
Enlarged Image
An image that is larger in size than the original object.
Example:
A magnifying glass creates an Enlarged Image of small text, making it easier to read.
Focal Length (f)
The distance from the vertex of a mirror or the optical center of a lens to its focal point. It is half the radius of curvature ($f = R/2$).
Example:
A camera lens with a short Focal Length (f) provides a wide-angle view, while a long f creates a telephoto effect.
Focal Point (F)
The point where parallel light rays converge after reflecting off a concave mirror or refracting through a converging lens, or appear to diverge from for convex mirrors and diverging lenses.
Example:
If you hold a magnifying glass (a converging lens) in sunlight, it can focus the sun's rays to a bright Focal Point (F), capable of starting a fire.
Geometric Optics
The study of light propagation in terms of rays, focusing on how light interacts with mirrors and lenses to form images.
Example:
Understanding how a camera lens focuses light to capture a clear photograph is an application of Geometric Optics.
Inverted Image
An image that is oriented opposite to the object, typically appearing upside down.
Example:
When you look at your reflection in a spoon (a concave mirror), your image might appear as an Inverted Image.
Lenses
Optical devices that form images by refracting (bending) light as it passes through them.
Example:
Eyeglasses use lenses to correct vision by bending light rays before they reach the eye.
Magnification Equation
A mathematical formula (M = -di/do = hi/ho) that relates the ratio of image height to object height to the ratio of image distance to object distance.
Example:
Using the Magnification Equation, a photographer can determine how much larger or smaller an object will appear in a photograph taken with a specific lens.
Mirror Equation
A mathematical formula (1/f = 1/do + 1/di) that relates the focal length of a mirror to the object distance and image distance.
Example:
If you know the focal length of a mirror and where an object is placed, the Mirror Equation allows you to precisely calculate where the image will form.
Mirrors
Optical devices that form images by reflecting light.
Example:
A funhouse mirror can distort your reflection, making you appear tall and thin or short and wide.
Plane Mirrors
Flat mirrors that produce virtual, upright, and same-sized images located as far behind the mirror as the object is in front.
Example:
When you look into a regular bathroom plane mirror, your reflection appears to be behind the glass.
Principal Axis
The imaginary straight line passing through the center of curvature and the vertex of a spherical mirror or the optical center of a lens.
Example:
When drawing ray diagrams, all key points like the focal point and center of curvature lie along the Principal Axis.
Radius of Curvature (R)
The distance from the vertex of a spherical mirror to its center of curvature.
Example:
A mirror with a large Radius of Curvature (R) will be less curved than one with a small R.
Ray Tracing
A graphical method used to determine the location, size, orientation, and type of an image formed by mirrors or lenses by drawing representative light rays.
Example:
Using Ray Tracing can help you visually confirm whether an image formed by a lens will be real or virtual before doing calculations.
Real Image
An image formed where actual light rays converge after reflection or refraction. It can be projected onto a screen.
Example:
The image projected onto a movie screen is a Real Image, formed by the converging light from the projector lens.
Reduced Image
An image that is smaller in size than the original object.
Example:
The image of a distant car seen in a car's passenger-side mirror is a Reduced Image.
Refracting/Refraction
The bending of light as it passes from one medium to another, caused by a change in the light's speed.
Example:
A straw in a glass of water appears bent at the water's surface due to the Refraction of light.
Upright Image
An image that has the same orientation as the object, meaning it is not inverted.
Example:
Your reflection in a bathroom mirror is an upright image, standing the same way you are.
Vertex (V)
The geometric center of a spherical mirror, where the principal axis intersects the mirror surface.
Example:
In ray tracing, the Vertex (V) is a convenient point to draw a ray that reflects at an equal angle to the principal axis.
Virtual Image
An image formed where light rays appear to diverge from, but do not actually converge. It cannot be projected onto a screen.
Example:
The reflection you see of yourself in a plane mirror is a virtual image.