Mirror Properties Printer Friendly Version
Plane Mirrors   Concave Mirrors Convex Mirrors
mirror shape flat mirror "caved in" "bowed out"
radius R R = 2f R = 2f
principal focus - - - F is "in front of the mirror" on the same side
as the incoming light
F is "behind the mirror" on the opposite side
as the incoming light
image
equation
di = - do 1/do + 1/di = 1/f
do is always positive
di is positive if real
di is negative if virtual
f is positive (convex)
1/do + 1/di = 1/f
do is always positive
diis always negative (virtual)
f is negative (concave)
magnification
equation
M = 1 M = | di / do | = | I / O | M = | di / do | = | I / O |
image
properties
virtual, upright, M = 1
sample ray diagram
image properties vary with object's position
sample ray diagrams

 do ∞ di = f real M 0 do > 2f 2f < di < freal M < 1 do = 2f di = 2freal M = 1 2f < do < f di > 2freal M > 1 do = f no image is formed - - - do < f 0 < di < -∞ virtual M > 1

virtual, upright, M < 1
sample ray diagram

 do ∞ di = -fvirtual M 0 any do < ∞ 0 < di < -fvirtual M < 1
rays Line up the top and bottom of the eye with the image, draw in a line - solid in the air, dotted behind the mirror, bounce it back to the object. Place arrows pointing away from the object, to the mirror, and then into the eye. #1 top of the object, parallel to the axis, strikes the mirror, reflects through F

#2 top of the object, passes through C, strikes the mirror, reflects back through C
#3 top of the object, passes through F, strikes the mirror, reflects parallel to the axis
#1  top of the object, parallel to the axis, strikes the mirror, lines up with F, reflects back (dot back reflection to F)
#2 top of the object, aims for C, strikes the mirror, reflects back (dot back reflection to C)
#3 top of the object, aims for F, strikes the mirror, reflects parallel to the axis (dot back parallel reflection)