Question

Take a convex lens and allow sunlight to fall on it. Hold a paper screen on the opposite side. Move the paper screen slowly away from the lens till a sharp bright spot is formed on the screen. Which phenomenon is responsible for this bright spot? What represents the sharp bright spot on paper screen? What is the focal length of this convex lens? Is the image of the sun always real?

Answer 1

The sharp bright spot is due to refraction of sunlight from convex lens. It represents the image of the sun. The distance of paper screen from the lens is called focal length of convex lens. The image of the sun is always real as it is obtained on the screen.