Physics - Loudoun County Public Schools



Ray Diagrams and the Lens EquationName: __________________EXAMPLE 1A 1.70-m tall person is standing 2.50 m in front of a camera. The camera uses a converging lens whose focal length is 0.0500 m. (a) Draw a ray diagram to determine whether the image is real or virtual. (b) Find the image distance, magnification and the height of the image on the film.EXAMPLE 2An object 1.2 cm high is placed 4 cm from a converging lens whose focal length is 12 cm. State whether the image is real or virtual, locate the image and find its height.EXAMPLE 3An object is placed 7.10 cm to the left of a diverging lens whose focal length is f = - 5.08 cm. (a) Draw a ray diagram to determine whether the image is real or virtual. (b) Find the image distance and magnification.Directions: For each of the problems below,(a) Draw to scale a correctly labeled ray diagram (b) Indicate whether the image is real or virtual(c) Measure the image distance with a ruler(d) Calculate the image distance using the given information(e) Calculate the magnification using the given information1. A 1.0-cm tall object is located 3.0 cm to the left of a converging lens whose focal length is 5.0 cm. 2. An object 1.5-cm tall is placed 4.5 cm in front of a converging lens whose focal length is 2.0 cm.3. An object 1.5-cm tall is located 7.0 cm to the left of a converging lens. The lens has a focal length of 2.5 cm.4. An object 1.5-cm tall is placed 6.0 cm in front of a diverging lens whose focal length is 2.0 cm.5. The focal length of a diverging lens is 4 cm. A 1.0-cm object is placed 8 cm to the left of the lens. Convex or converging lenses form real and inverted images, when the object is placed at a distance greater than the focal length. The images are magnified if object distance is between f and 2f and diminished if beyond 2f. Convex lenses form magnified, virtual and upright images if the object distance is less than f. Concave or diverging lenses always form virtual, upright images. They could be either magnified or diminished depending on the object distance. Virtual images cannot be captured on a screen whereas real images can be. Focal length is positive for convex and negative for concave lenses. Image distances are positive if they are on the right side of the lens (real, inverted image) and negative if they are on the left side of the lens (upright, virtual image). Height is negative for inverted image and positive for virtual image. Magnification is positive for a virtual image and negative for a real image.LENS PROBLEMS 1. An object is placed 20.0 cm in front of a converging lens of focal length 10.0 cm. Find the image distance and the magnification. Describe the image. 2. Sherlock Holmes exams a clue by holding his magnifying glass (with a focal length of 15 cm) 10 cm away from an object. Find the image distance and the magnification. Describe the image. 3. An object is placed 30 cm in front of a diverging lens of focal length 10 cm. Find the image distance and magnification. Describe the image. Draw a ray diagram to support your description. 4. Consider the image formed by a thin converging lens. Under what conditions will the image be a. inverted? b. upright? c. real? d. virtual? e. larger than the object? f. smaller than the object? 5. A concave lens is used to form a virtual image of an object. The object is 80 cm in front of the lens and the image is 40 cm in front of the lens. Determine the focal length of the lens. Draw a ray diagram for this situation. ................
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