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Converging lens HTML5

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Here you have the ray diagrams used to find the image position for a converging lens. You can also illustrate the magnification of a lens and the difference between real and virtual images.

Ray diagrams are constructed by taking the path of two distinct rays from a single point on the object.  By convention rays travel from left to right:

  • A light ray that enters the lens is an incident ray.
  • A ray of light emerging from the lens is an emerging ray.
  • The optical axis is the line that passes through the center of the lens. This is an axis of symmetry.

The geometric construction of an image of an object uses remarkable properties of certain rays:

  • A ray passing through the center of the lens will be undeflected.
  • A ray proceeding parallel to the principal axis will pass through the principal focal point beyond the lens, F'.

Virtual images are produced when outgoing rays from a single point of the object diverge (never cross). The image can only be seen by looking in the optics and cannot be projected. This occurs when the object is less than the focal length of the lens from the lens (case of the magnifying glass).

Real images are produced when outgoing rays from a single point of the object come to a focus. This kind of image can be projected on a screen. This occurs when the object is further than focal length.

Click and drag the body horizontally.
Click and drag the head vertically.
Click and drag the focal point F'.

Learning goals

  • To illustrate the construction of ray diagrams for a converging lens.
  • To define vergence of a lens.
  • To introduce the property of magnification.




Learn more

The distance OF' is called the image focal length. It is sometimes denoted f', not to be confused with the image focal point noted F'.

Vergence, V = 1/f' is a value commonly used in optics…

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