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
“Objects in Mirror Are Closer Than They Appear”
The passenger-side mirror on a car is a convex mirror, as are the round security mirrors in store corners.
What kind of image does a convex mirror always form?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A store’s convex security mirror has a radius of curvature of 1.2 m. Determine the distance from the mirror to its (virtual) focal point.
C2. Why are the objects “closer than they appear”?
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. Place a check mark in three boxes to indicate the applications for which a convex mirror is the best choice.
C5. Can a convex mirror ever project an image onto a screen?
C6. A car company considers replacing the flat driver’s-side mirror with a convex mirror. Identify one benefit and one drawback of this design change.