University of Virginia
Physics Department

## Curved Mirrors

A Physical Science Activity

### Student Activity

Materials

• Convex mirror
• Concave mirror
• Plane mirror
• Birthday candles
• Modeling clay
• Meterstick
• Index card
• Matches

Procedure

1. 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.
2. 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 OTHER PERSON!)

 Figure 2: One possible arrangement of the candle, mirror, and index card for examining real images.

3. 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.
4. 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 formed.