Investigating the Properties of Lenses

Investigating the Properties of Lenses

Introduction: Refraction is the bending of a wave due to a change in media. A lens is a molded optical device with two opposite surfaces, one of which is curved, that bends light so that it converges or diverges to form an image. The focal point of a lens is the point at which the light converges or seems to diverge from when refracted using an optical device. The focal length is the distance from the optical device to the focal point. The object distance is the distance from the lens to the object. The Image distance is the distance from the lens to the image of the object that is created. A real image is where rays converge, but a virtual image is where the rays appear to converge.

Problem:

Variables: Independent Variable: Object Distance

Dependent Variable: Image Distance

Constants: Lens, Candle

Procedural: Our first step was to set up our station by putting the meter stick in the holders and attach the candle and card using their holders. We then found the focal length by going to the other side of the room, focusing the image, then measuring the distance to the focal point. We then went back to our station and measured the image distance for several object distances.

Methods and Materials:

Focal Length

1. With the room lights turned off, hold a lens so that light from a distant source passes through it

2. Hold a piece of paper so that the light that has passed through the lens makes a spot on the paper

3. Move the paper back and forth until the spot is smallest

4. measure the distance from the lens to the minimum-diameter spot

Image Properties and the Relationship between Object and Image Distances

1. Set up an optics bench using a meter stick

2. place and candle at one end of the meter stick and a screen at the other end

3. hold the lens 50cm from the candle (object distance)

4. move the screen until a clear image of the candle appears on the screen, if possible

5. measure the distance from the lens to the screen and record it in the table

6. Record the following properties also: Is the image real or virtual? Is it upright or inverted? Is it enlarged, reduced, or the same size and the object?

7. Reduce the object distance by 5cm and repeat steps 3-7

8. repeat step 7 until the final object distance is 10cm

9. Graph the image distance (vertical axis) vs. the object distance (horizontal axis)

Materials:

• Meter Stick

• Meter Stick Holders (2)

• Candle