- University of Virginia
- Physics Department
A Physical Science Activity
2003 Virginia SOLs
- compare and contrast the properties and uses of concave and convex mirrors;
- compare and contrast real and virtual images;
- describe practical uses of curved mirrors.
What images are produced when mirrors are curved?
Curved mirrors are like plane mirrors in that they too have
smooth, shiny surfaces that reflect light. The surface can either
curve out (convex) or in (concave) as shown in Figure 1.
Convex mirrors are commonly found in cars as rear-view mirrors.
They offer a wider view than a plane mirror, but the images are
smaller than they would be in a plane mirror. To help drivers, these
mirrors will frequently include the warning that "Objects in mirror
are closer than they appear." The images produced are also called
virtual images because they appear to form behind the mirror and
cannot be projected on a screen.
Concave mirrors are commonly found as reflectors in flashlights
and some telescopes. They are used in solar ovens, and though one
cannot see the reflected electromagnetic rays, a satellite dish is
essentially a concave mirror. When an object is beyond the focal
point of a concave mirror, the image formed will be real and
inverted. (A real image can be projected on a screen.) If the object
is very far away and the light rays are parallel when reaching the
surface of the mirror, the image will form at the focal point. If the
object emitting the light rays is at the focal point, the reflected
rays will not form a real image. Instead, the reflected rays leave
the surface of the mirror parallel to one another. (This is the way a
flashlight or car headlight is constructed.) A third possibility is
if the object is between the focal point and the mirrored surface. In
this case, the image will be virtual, larger, and right side up.
To print out the Student Copy only,
- Convex mirror
- Concave mirror
- Plane mirror
- Birthday candles
- Modeling clay
- Index card
These activities can be performed in small groups or as
- Hold the convex mirror in front of you. Move the mirror toward
and away from you and observe the image formed. Hold a plane
mirror in front of you. Move it toward and away from you to
observe the image formed. Hold the concave mirror in front of you.
Move it toward and away from you and observe the images formed.
Compare the images with respect to size and orientation.
- Measure the focal length of the concave mirror by focusing the
sun's image on an index card. Reflect the sun's rays onto the card
and move the mirror toward and away from the index card until a
small dot is focused. Measure the straight-line distance from the
card to the center of the mirror. This is the focal distance of
the mirror, and the image is located at the focal point. (DO NOT
LOOK DIRECTLY AT THE SUN OR FOCUS THE SUNLIGHT ON YOURSELF OR ANY
Figure 2: One possible arrangement
of the candle, mirror, and index card for examining real
- Place a lit birthday candle mounted in modeling clay on a lab
table. Hold the concave mirror a distance equal to the focal
length from the candle. Dim the room's lights and hold the index
card away from the mirror and candle to view the reflected light
(figure 2). Compare the amount of light reaching the card when the
mirror is in position and reflecting the candlelight to when there
is no reflection of light and the candle sheds only direct light
on the card.
- Position the mirror so it is at a distance twice that of the
focal length from the candle. Place the index card at a distance
near the focal length from the mirror and move it towards and away
from the mirror until an image of the flame forms on the index
card. The image will be inverted. Continue to vary the distances
among the candle, screen, and mirror to investigate the images
- Research other uses of curved mirrors.
- Build a solar oven.
- Research satellite dish design and technology.
Students with Special Needs
Adapt as needed to children who have physical disabilities.
Click here for further
information on laboratories with students with special needs.
- Accuracy of student data will provide information on student
- Students predict images formed when a light source and mirror
are in a variety of orientations.
- Students predict position of light source when images and
mirrors are in a variety of orientations.