PhysicsLAB: Mirror Properties

Plane Mirrors

Concave Mirrors

Convex Mirrors

mirror shape

flat mirror

"caved in"

"bowed out"

radius

∞

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

d_i = - d_o

1/d_o + 1/d_i = 1/f

d_o is always positive
d_i is positive if real
d_i is negative if virtual
f is positive (convex)

1/d_o + 1/d_i = 1/f

do is always positive
d_iis always negative (virtual)
f is negative (concave)

magnification
equation

M = 1

M = | d_i / d_o | = | I / O |

image
properties

virtual, upright, M = 1
sample ray diagram

image properties vary with object's position
sample ray diagrams

d_o ∞	d_i = f real	M 0
d_o> 2f	2f < d_i < f real	M < 1
d_o= 2f	d_i = 2f real	M = 1
2f < d_o < f	d_i> 2f real	M > 1
d_o= f	no image is formed	- - -
d_o< f	0 < d_i < -∞ virtual	M > 1

virtual, upright, M < 1
sample ray diagram

d_o ∞	d_i = -f virtual	M 0
any d_o< ∞	0 < d_i < -f virtual	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)