Giant Mirrors Lesson Plan Amount of time demo takes: 1-2 mins.
Try this at home!
Materials
● Two giant mirrors
Set-up Instructions and Instructional Procedure
1. Take the mirrors out of the box.
2. Make sure that you have a stable surface to set them on where they won’t
get knocked off.
3. Invite visitors to take a look in the two different mirrors. Play with
distances and angles, asking them what they see and discussing how these
mirrors work.
SAFETY! Safe demo! Use any appropriate care in crowds so that no one
knocks the mirrors over.
Lesson’s Big Idea
● Grade 6-12: Convex mirrors create a ‘fisheye’ effect that enables you to
see a wider range. A concave mirror produces an upside-down image at
long distances, but up close creates right-side up, magnified images. An
image can be real or virtual depending on where an object is relative to a
mirror.
● Grade K-6: Convex mirrors make you look small and concave mirrors make
you look big.
Background Information
● The basic rule of mirrors is this: The angle of
incidence equals the angle of reflection.
All that means is that light bounces off at the
same angle as it hit the mirror (relative to
the perpendicular/normal line, which you can
think of as the ‘sight line’). The reflecting
light creates what is called an image of the
1/3 original object. Weirdly (but because of some neat light science), the
image can be real and appear to in front of the mirror or virtual, looking
like it is ‘inside’ or ‘behind’ the mirror.
● There are two points to keep in mind when discussing mirrors: The center
of curvature and the focal point. The center of curvature (COC) is the
center of the imaginary sphere you would get if you drew one with the
curve of the mirror. The focal point is halfway between the mirror and the
center of curvature -- it is where the light rays come together after
reflecting. See the picture below for an explanation!
● Convex mirrors bulge outward. At the edges, a convex mirror reflects at a
wider angle than near its center (hence that ‘’fisheye’’ effect). As a result,
the reflection is small; it looks far away or ‘within’ the mirror because these
mirrors produce virtual images. The light bounces off and spreads out from
the mirror, so it will never come back together in front of the mirror to
make a real image. The smaller size of the images means that you can see
more with these surfaces.
● One example of convex mirrors in the real world: Safety mirrors on cars.
The distortion in the mirrors is the reason they often say ‘‘objects in mirror
are closer than they appear.’’
● Concave (or converging) mirrors are the ones that curve in. What you see
depends on where you stand.
a. When you look at a convex mirror from further away than its’ center
of curvature, the image will be upside-down and smaller than real
life. If you, the object, is right at the COC, your image will still be
2/3 upside-down but will be the same size as real life.
b. If you are in between the focal point and the center, your image gets
bigger, is upside-down, and is behind you.
c. Standing at the focal point, you won’t see anything. The rays don’t
converge or diverge.
d. Lastly, if you are closer to the mirror than the focal point, you will look
huge! This image is unlike the other three cases, because it is virtual
-- it looks like you’re inside the mirror.
● Just a few examples of practical uses for concave mirrors include
makeup/beauty mirrors. They are also used to focus sunlight to a single
point -- this can be used to start a fire or light the Olympic torch!
Assessment/sample questions to ask
1. Why are convex mirrors useful for car mirrors and security mirrors?
2. Would you rather examine something small using a convex or concave
mirror?
3. What is focal length? Focal point?
4. What is an ‘image?’
Clean Up
● Properly store the mirrors! Please make sure they are securely in their box
with foam or another stuffing so they are not damaged during
transportation. If the mirrors have gotten grungy during the day, clean
them off using a soft cloth and windex or similar.
References
● How Stuff Works: Mirrors
(http://science.howstuffworks.com/innovation/everyday-innovations/mirro
r3.htm)
Next Generation Science Standards
● K-5
○ 1-PS4-2
● 6-8
○ MS-PS4-2
● 9-12
○ HS-PS4-1 3/3