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Image Formation on Convex Lenses

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Image Formation on Convex Lenses


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Students learn about the special rays and image formation on a convex lens.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • After completing this Activity Object, students will be able to:
  • Predict image formation as a consequence of refraction through a thin convex lens.
  • Show the refraction of special rays in a convex lens.
  • Perform experiments for different locations of an object in a convex lens.
  • Draw the formation of an image in a convex lens.
  • Calculate the location and height of an image in a convex lens.

Everything You'll Have Covered

Image formation on lenses and mirrors is a direct consequence of refraction and reflection. This approximation of the true behavior is called "geometrical optics." It is most useful in its application to a number of practical devices, including eyeglasses, telescopes, microscopes, and many types of scientific instruments. The central assumptions for this method are that light travels in straight lines if unobstructed and that these lines do not interfere with each other. We call these lines "rays." A ray may be thought of as the trace of the trajectory of a photon if we consider only the particle character of light.

When a light ray strikes a surface, it may be reflected or refracted. Reflection occurs when a ray strikes the surface of a mirror. The angle of incidence equals the angle of reflection with respect to the line normal to the plane at the point at which the ray strikes. The light ray travels in a straight line and bounces off the mirror into a new straight line. However, refraction occurs when light travels from one medium to another, such as the glass of a lens. For example, the ray traveling in a straight line in the air changes direction into another straight line when it enters the transparent glass of the lens. The angle of incidence is related to the angle of refraction (usually given the same symbol as reflection, by Snell's Law. In this case, where are the refractive indices of air and water. The treatment of curved convex or concave surfaces between media and image formation follows the same law.

The above description of refraction is merely a statement of what happens when light is refracted. Although it has important predictive power, it says nothing about how it happens. A deeper view, in itself still an approximation, is a statement of Fermat's Principle. This principle states that light takes the path that requires the shortest time.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should know the difference between real and virtual images.
Course Physics
Type of Tutorial Concept Development
Key Vocabulary 2F, converging lenses, convex lenses