Question

A real image is formed by a particular lens. The separation between the object and the image is 36 cm, measured along the principal axis. The image is just half the size of the object.

1. What kind of the lens must be used to produce this image?
2. How far the object is placed from the lens?
3. What is the focal length?
4. Use the graphical method to illustrate the principle of the image formation.

Answer 1

ANSWER: a. Since it is given that the image is real, therefore the lens must be a converging one, i.e. Convex Lens b. Since it is given that the image is smaller, therefore the distance of the object from the lens must be greater than 2 x focal length of the lens. Let us calculate it's value: u = distance of the object from the lens v = distance of the image from the lens m = magnification of the image Using the relation: m=; Given that image size is half of object, i.e. m Also given that u + = 36 3u = 72 u = 24 cm (Thus, v = 36 - 24 = 12 cm) C. Now the focal length must me less than 24/2. Let us calculate it's value: f = focal length of the lens Using the relation: - 1 1 1 + i 24 x 12 = f = 8 cm

Convex Lens 36cm

ANSWER: a. Since it is given that the image is real, therefore the lens must be a converging one, i.e. Convex Lens b. Since it is given that the image is smaller, therefore the distance of the object from the lens must be greater than 2 x focal length of the lens. Let us calculate it's value: u = distance of the object from the lens v = distance of the image from the lens m = magnification of the image Using the relation: m= Given that image size is half of object, i.e. m = Also given that u + v u+ = 36 3u = 72 u = 24 cm (Thus, v = 36 - 24 = 12 cm) C. Now the focal length must me less than 24/2. Let us calculate it's value: f = focal length of the lens Using the relation: 24 x 127 f = 8 cm

Convex Lens 36cm