Convex Mirrors

Virtual Images

Review

• For any position where an object is in front of a Concave Mirror past the focal point, the rays of light converge, forming a real image

C F

Real, inverted image of the pencil.

Review

• An object on F will disapear.

• But if it goes past f it shows up again…

C F

Virtual Images in Concave Mirrors

• If the object is in front of the focal point, the rays of light diverge after hitting the mirror.

C F

Virtual Images in Concave Mirrors

• Note: This arrow lines up with the focal point… Everything else is like before. Almost.

C F

Virtual Images in Concave Mirrors

• When do the red lines cross? So how do we see a reflection?

C F

Virtual Images in Concave Mirrors

• Extend the red lines to the OTHER side of the mirror. (Inside the mirror and wall)

C F

Virtual Images in Concave Mirrors

• This is where you EYE SEES the image:

C F

RealPencil Image

Virtual Images in Concave Mirrors

• Since it’s on the OTHER side of the mirror, it’s a VIRTUAL image.

C F

RealPencil Image

Real vs Virtual Image

C F

RealPencil

Images on the same side of the mirror as the

object: REAL IMAGES

Images on the other side of the mirror (in the wall):

VIRTUAL IMAGES

Convex Mirrors

• Convex Mirrors are also called diverging mirrors. Light rays never intersect once they hit the mirror.

F C

The focal point and center of curvature still exist, they are just on the OTHER side of the mirror now.

Convex Mirrors

• We can use the same trick as before to make the Laws of Mirrors work.

F C

Law #1

• We can use the same trick as before to make the Laws of Mirrors work.

F C

Law #1

• We can use the same trick as before to make the Laws of Mirrors work.

F C

Law #2

• Law 2 starts out going toward the focal point.

F C

Law #2

• Then bounces back parallel. (Remember to use the trick)

F C

Example

• Let’s put the two together.

F C

Example

• Law 1:

F C

Example

• Law 2:

F C

Example

• Law 2:

F C

A Note on Focal Points

• For Convex Mirrors, since the focal point is on the opposite side of the mirror from the object, the value given will be negative.

• Example: A focal point of -9 cm indicates the point F is 9 cm from the mirror on the opposite side of the actual object

F

9 cm

Magnification and Convex Mirrors

• As an object gets farther away from a Convex Mirror, the image gets smaller and smaller.

• As the object gets closer, the object gets nearer to the actual size of the object.

Object vs. Virtual Image