The Focal Point of a Convex Lens


Point Source




Part 1

Click on start to begin. A beam of light emitting parallel rays will be shown. Click and drag on the source to move it around. Drag the small red dot to indicate the focal point of the lens. Does the focal point of the lens depend on the location of the source?

When a ray is parallel to the axis of the lens, through which point does the transmitted light always pass?

Part 2

Click on Point Soruce to change the light source to a point source. Move the point source around. The red dots indicate the locations of the focal points of the lens.

Which rays pass through the back focal point?

How does the location at which the lens converges the light from the point source change as the source is moved from the left towards the front focal point?

What happens to the light transmitted by the lens when the source is between the front focal point and the lens.

Part 3

Click on Location to see three different locations at which an object will be placed. predict the order of the image formed by the lens from left to right. Use A to denote the location of image formed when the object is placed at point A, B for the location of the image when the object is placd at point B and C for the location of the image formed when the object is placed at point C. The red dots indicate the location of the lens's focal points.

Click on Object to get an object. Move the object to each of the locations to test your prediction.

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Last Updated: August 21, 2009