Convex Mirrors
Why objects in the mirror look smaller and farther away
Do Now: The passenger-side mirror on a car says “Objects in mirror are closer than they appear.” Why would a car company use a mirror that fools you?
A convex mirror shows a much wider view. The trade-off is that every image is smaller, so cars look farther away than they really are.
A. Principal Rays for a Convex Mirror
For a convex mirror, F and C are behind the mirror. The rays aim at them, and the reflected rays are traced backward with dashed lines.
Ray 1 — Parallel Ray
Travels parallel to the principal axis, then reflects as if it came from F behind the mirror.
Ray 2 — Focal Ray
Aims toward F behind the mirror, then reflects parallel to the principal axis.
Ray 3 — Center Ray
Aims toward C behind the mirror and reflects back on itself.
B. The Image Is Always the Same Type
Object far from the mirror — click Next to draw it step by step.
Object close to the mirror — click Next to draw it step by step.
Describe both images using L-O-S-T. What changes when the object moves closer?
L: behind the mirror, between the mirror and F O: upright S: smaller T: Virtual
Moving closer makes the image a little larger and closer to the mirror, but it is always virtual, upright, and smaller.
Explore: Convex Mirror
Drag the orange object. Turn rays on and off with the check boxes.
C. Convex Mirrors at Work
Passenger-side car mirrors: a wide field of view, but cars look smaller and farther away.
Store security mirrors: one mirror in the corner shows a whole aisle.
Blind driveways & intersections: drivers can see around a corner.
School bus mirrors: the driver can see the area right in front of the bus.
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Where is the focal point of a convex mirror?
2. A convex mirror always forms an image that is
3. Why are convex mirrors used for store security?
4. A ray aimed at the focal point of a convex mirror reflects
5. As an object moves closer to a convex mirror, its image