DISCUSSION:
Lenses are used to bend light. Any ray of light traveling along the same path through a lens will ALWAYS follow the same path. This is why lenses can be used to help us see, to magnify, or to make things appear closer. There are two types of lenses, concave (or diverging) and convex (or converging). To converge means to come together, therefore convex lenses make light "squeeze" together. To diverge means to spread apart, so a concave lens makes light move apart. The optical axis you will draw is simply an imaginary line that bisects any lens horizontally and is used as a reference point.

PURPOSE:
The purpose of this activity is to discover what happens to light when it passes through different types of lenses.

MATERIALS: 2-3 round water lenses, ruler, 1 square water lens, and a ray box or a laser

PROCEDURES:

USING RAY BOX

1) Make sure the shield on the ray box is positioned so as to allow three rays of light to be produced.

2) Shine the three rays into all of your round lenses. (Use one lens at a time)

QUESTION 1: What happens to the rays as they exit the lens?

QUESTION 2: What type of lens are the round lenses?

3) Try placing two round lenses one after the other. Can you make the light go straight again? Draw a picture showing how your arranged then lenses and how the light looked as it went from the ray box all the way through both lenses.

4) Pour half of your water from a large round lens into a square lens. Discard the remaining water. Place the empty large round lens inside the square lens with the water. Carefully push the round lens down and hold it at the bottom.

5) Shine the 3 rays into the square lens.

QUESTION 3: What happens to the light?

QUESTION 4: What type of lens is the square len?

USING RAY BOX

6) Place the circular lens in the center of a piece of paper. Make sure it is filled with water with a pinch of magnesium carbonate. Draw a line around the lens. Take a ruler and bisect the lens by drawing a line that goes through its center and runs the long way across the paper. Label this line the OPTICAL AXIS.

ALL LIGHT MUST BEGIN ABOVE THE OPTICAL AXIS AS IT LEAVES THE RAY BOX. IT MAY CROSS THE OPTICAL AXIS BEFORE ENTERING THE LENS HOWEVER.

7) Use the pins to guide you. Shine a ray of light parallel to the optical axis. Trace the path of the ray as it enters and exits the lens. Place an arrow head on the ray to indicate direction. Label the ray RAY 1.

6) Shine a ray of light so that it exits the lens below the optical axis and parallel to the optical axis and crosses RAY 1. Again trace the path of the ray and place arrow head on the the ray. LAbel the ray RAY 2.

7) Shine a ray of light so that it doesn't bend as it passes through then lens AND crosses RAY 1 and RAY 2. Trace the ray, add arrows, and label the ray RAY 3.

8) Look at the drawing of the three rays. Mark the place where RAY 1 crosses the optical axis focus 2. Label the place where RAY 2 crosses the optical axis focus 1. Measure the distance from the center of your lens to each focal point along the opitcal axis (the line you drew). This is your focal length (It should be the same on both sides if you performed the activity correctly)

QUESTION 5: What is the focal length for your lens?

NO LAB WRITE UP FOR THIS ACTIVITY. JUST TURN IN DIAGRAM AND QUESTIONS.