Pupil sheet · Lenses and images
Lenses and images — return questions
Name ______________________ Date ____________
Use one to two weeks after the lessons. Keep the notes and the lesson closed.
1. define / state / describe / determine
(a) Define the principal focus of a converging lens. (b) A parallel beam of light passes through a converging lens of focal length 6.5 cm. State how far from the lens the rays cross the principal axis, and describe what a screen 13 cm behind the lens shows. (c) An object stands on the principal axis exactly at the principal focus of a converging lens. From its tip, a pupil draws the ray parallel to the axis and the ray through the centre of the lens. Describe how these two rays leave the lens, and state what this tells you about the image. (d) A converging lens of focal length 25 cm forms a real, enlarged image of a small toy figure on a screen. Determine the range of distances from the lens in which the figure must be.
(a) The principal focus
(b) The parallel beam and the screen
(c) The two rays from an object at F
(d) Where the figure must be
2. explain / describe / state
(a) Explain why a virtual image cannot be caught on a screen. (b) Supplement. A converging lens of focal length 5.0 cm is used as a magnifying glass to read the date on a coin. Describe where the coin must be and where the eye goes. (c) Supplement. In a ray diagram for a magnifying glass, the two rays from the tip of the object spread apart after the lens. State how you find the tip of the image. (d) Supplement. A long-sighted woman reads a book through her reading glasses. Still wearing them, she looks up at a clock across the room, and it looks blurred. State the kind of lens in her glasses, and explain why the clock looks blurred through them.
(a) Why no screen
(b) Supplement: the magnifying glass
(c) Supplement: the tip of the image
(d) Supplement: the reading glasses and the clock