Glossary
Center Ray
A principal ray that strikes the center of the mirror and reflects at the same angle relative to the principal axis.
Example:
The center ray is useful because its reflection angle is easy to determine by symmetry.
Concave Mirror
A spherical mirror that curves inward, causing parallel incident light rays to converge.
Example:
A dentist uses a small concave mirror to get a magnified view of your teeth.
Converging Mirror
Another name for a concave mirror, indicating its ability to bring parallel light rays together at a focal point.
Example:
A satellite dish acts like a large converging mirror, focusing radio waves to a receiver.
Convex Mirror
A spherical mirror that bulges outward, causing parallel incident light rays to diverge after reflection.
Example:
The passenger-side mirror on a car is a convex mirror, providing a wider field of view but making objects appear farther away.
Diverging Mirror
Another name for a convex mirror, indicating its ability to spread out parallel light rays after reflection.
Example:
Security mirrors in stores are diverging mirrors, allowing staff to see a broad area.
Focal Length ($f$)
The distance from the mirror's surface to its focal point.
Example:
A mirror with a shorter focal length will bring light to a focus closer to its surface.
Focal Ray
A principal ray that passes through (or is directed towards) the focal point before reflecting parallel to the principal axis.
Example:
The focal ray is the inverse of the parallel ray, demonstrating the reversibility of light paths.
Image Formation
The process by which light rays from an object are reflected by a mirror to create a representation of that object.
Example:
When you look into a spoon, you see your upside-down reflection, which is an example of image formation.
Image Location
The position where an image is formed by a mirror, determined by the object's distance and the mirror's focal length.
Example:
Knowing the mirror's properties helps predict the image location for any object placed in front of it.
Image Magnification ($M$)
The ratio of the image height to the object height, indicating whether the image is enlarged, reduced, or the same size.
Example:
If an object appears twice as tall in a mirror, the image magnification is 2.
Mirrors
Optical devices that reflect light to form images.
Example:
A funhouse mirror uses a curved surface to distort your reflection in amusing ways.
Parallel Ray
A principal ray that travels parallel to the principal axis before reflecting through (or appearing to come from) the focal point.
Example:
When drawing a ray diagram, the parallel ray is always the first one to draw from the top of the object.
Plane Mirror
A flat mirror that produces virtual, upright, and same-size images.
Example:
Your bathroom plane mirror shows you an image that is the same size and distance away as you are.
Principal Axis
An imaginary straight line passing through the center of curvature and the focal point of a spherical mirror, perpendicular to the mirror's surface.
Example:
All measurements for object and image distances are typically taken along the principal axis.
Principal Rays
Specific, easily traceable light rays used in ray diagrams to locate the image formed by a mirror.
Example:
The three principal rays (parallel, focal, and center) are sufficient to accurately draw an image.
Radius of Curvature ($R$)
The radius of the sphere from which a spherical mirror's surface is a part; it is twice the focal length ($R=2f$).
Example:
A large satellite dish has a significant radius of curvature, allowing it to collect signals over a wide area.
Ray Diagrams
Graphical representations using specific light rays to determine the characteristics (location, size, orientation, type) of an image formed by a mirror.
Example:
Drawing ray diagrams is a crucial skill for visualizing how mirrors form images without complex calculations.
Real Focal Point
The point in front of a concave mirror where parallel incident light rays actually converge after reflection.
Example:
If you hold a concave mirror in sunlight, the sun's rays will converge at its real focal point, creating a hot spot.
Real Images
Images formed when actual light rays converge at a point; they can be projected onto a screen.
Example:
A projector creates a real image on a screen by focusing light rays from a slide or digital source.
Sign Conventions
A set of rules used in optics to assign positive or negative signs to distances and heights, indicating their direction or nature.
Example:
Using sign conventions, a real image distance is typically positive, while a virtual image distance is negative.
Spherical Mirror
A mirror that has a reflecting surface which is a section of a sphere, including both concave and convex types.
Example:
Telescopes often use large spherical mirrors to gather and focus light from distant stars.
Virtual Focal Point
The point behind a convex mirror from which parallel incident light rays appear to diverge after reflection.
Example:
For a convex mirror, the light rays spread out as if they originated from a virtual focal point behind the mirror.
Virtual Images
Images formed when light rays only appear to diverge from a point; they cannot be projected onto a screen.
Example:
The image you see of yourself in a plane mirror is a virtual image.