GCSE Physics Tutorial: Ray Diagrams for Convex and Concave Lenses
Ray diagrams are a powerful tool used to visualise the behaviour of light rays as they pass through lenses. They help us understand how lenses create images and determine whether those images are real or virtual, inverted or upright. In this tutorial, we'll learn how to draw ray diagrams for both convex and concave lenses.
Ray Diagrams for Convex Lenses:
Case 1: Object Beyond Focal Point (Real Image Formation)
Start with an arrow (representing the object) placed beyond the focal point (F) on the left side of the lens.
Draw a ray parallel to the optical axis that passes through the focal point after being refracted by the lens.
Draw a ray passing through the center of the lens, which continues in the same direction without changing its path.
The rays intersect at a point on the opposite side of the lens. This is the real, inverted image formed by the convex lens.
Case 2: Object at Focal Point (No Image Formation)
Place the object exactly at the focal point (F) on the left side of the lens.
Draw a ray parallel to the optical axis. After being refracted by the lens, it will emerge parallel to the optical axis, indicating that the rays never converge to form an image.
Case 3: Object Between Focal Point and Lens (Virtual Image Formation)
Place the object between the focal point (F) and the lens on the left side.
Draw a ray parallel to the optical axis. After being refracted by the lens, it will appear to emerge from the focal point on the right side.
Draw a ray passing through the center of the lens, which continues in the same direction without changing its path.
The rays appear to diverge from a point on the right side of the lens. This is the virtual, upright image formed by the convex lens.
Ray Diagrams for Concave Lenses:
Concave lenses always form virtual, upright images regardless of the object's position. The ray diagrams for concave lenses are similar to those for convex lenses, but with some differences due to the diverging nature of the lens.
Draw a ray parallel to the optical axis. After being refracted by the lens, it appears to come from the focal point on the left side.
Draw a ray from the top of the object through the center of the lens. After refraction, it continues in a straight line.
The rays appear to diverge from a point on the left side of the lens. This is the virtual, upright image formed by the concave lens.
Ray diagrams provide a visual representation of how light rays interact with lenses, helping us understand image formation and the characteristics of the images produced by convex and concave lenses.
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