An instructor challenges a team of students to verify experimentally that only one of…
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
An instructor challenges a team of students to verify experimentally that only one of the two common thin lens types can project a sharp real image of a luminous object onto a screen, whereas the other cannot, regardless of object placement. The students are given the following equipment:
• One thin convex lens and one thin concave lens (focal lengths unknown)
• A bright filament lamp mounted on a movable carriage
• An adjustable screen that can slide freely along an optical rail
• Metersticks and lens holders
They must design a single experimental procedure that demonstrates the stated claim for both lenses and then explain the optical reasoning that justifies the conclusion.
(1) Design a step-by-step experimental procedure that uses the provided equipment to test each lens for its ability to form a real image on the screen. Include how the students will know whether an image is real or not for each lens.
(2) Predict the outcome for the convex lens and for the concave lens. Your prediction must include whether a sharp image on the screen will be obtained and an explanation grounded in qualitative ray behaviour for each lens.
(3) Suppose the team additionally wants to estimate the focal length of the concave lens even though it cannot form a real image on its own. Propose and justify a method, using only the given equipment, that would allow them to determine an approximate value for the focal length’s magnitude.