Task id16285

There is a coin at the bottom of a vessel of depth d filled with water. At what height h from the surface of the water should an electric light bulb be placed so that its image, given by the rays reflected from the surface of the water, coincides with the image of the coin, given by the refracted rays? How can one establish a coincidence between the images of a light bulb and a coin by direct vertical observation? (Fig.)