Lesson: Thin Lenses

Activity 1. For today's activity create ray diagram for specified locations. Indicate your measurements and scales. Take a picture or scan.

Note: Don't copy the answer on the internet or else you may get zero in this activity

a. Concave - object at C and object between C and F (boys) object beyond C and object at F (Girls)

b. Convex - object beyond C (boys) and object at C (girls).

For tutor: For further understand this activity you may see the lessons below.

m DEPARTMENT OF PHYSICS Physics 21900 General Physics ll Electricity, Magnetism and Optics Lecture 19 Chapter 22.4-6 Thin Lenses Fall 2015 Semester Prof. Matthew Jones Converging Lenses All possible cases: Case 1: so and si positive an r r a he Inverted smaller image Upright larger image (virtual) Diverging Lens Parallel ray Object Object Focal ray Principal axis FL. FR F, Image C FR Central ray Diverging lens B A Object locations So positive and s; negative. 2F 2F Image locationsExample #1: A 6.0-cm tall candle is placed a distance of 7.0-cm from a convex lens which has a focal length of 16.0-cm. Determine the image distance and the image size. 1 Five cases - which one applies? + So Si Object hi Si Buyoud 2F m = = ho So Object 2F At 2F So = 7 cm f = 16 cm ho = 6 cm Image 1 1 1 Si Object m= - 26 Image Between 21 and F So 2F Si So -12.44 cm = Object 16 cm 7 cm 7 cm At F Image = -0.080 cm- = +1.78 At infinity 1 hi = hoxm unnge Si = Between F -0.080 cm-1 = (6 cm) x (1.78) and lens Object Si = -12.44 cm hi = +10.66 cmThe magnifying glass The closer an object is to your eye, the more detail you can see. O For a normal eye, the shortest distance for clear vision is about N=25 cm. Si 1. Unaided eye: h m= object 25 cm h So ho hi ho his m image S; So N S ~ 25 cmThe magnifying glass Converging lens with short focal length placed close to eye O Object is placed near focal length of lens. 2. Lens with short focal length: object . - m'= hi image N ho S hi hi m x-o fi S; So~f h. m'x ho/ /f 25 cm Si ME e f (in cm) mx 25 cm S\fWhy Lenses Work Normal line , 1, Normal line Refraction of light rays by Refraction of light rays a converging lens. by a diverging lens. Terminology Vertical Axis An imaginary line passing through the exact center of the lens is referred to as the Principal principal axis. Axis 2F F A lens also has an imaginary Focal vertical axis that bisects the Length lens. Light rays on either side of the lens parallel to the principal axis will either converge or diverge. For a converging lens, parallel light rays will converge to a point. This is the focal point (F) of the converging lens. A point that is twice the distance from the lens as the focal point is labeled 2F.2F Terminology For a diverging lens, parallel light rays diverge and can be traced backwards until they intersect at 2F a point. This intersection point is known as the focal point (F) of a diverging lens. The action of a lens is symmetric. This means that each lens has two focal points - one on each side of the lens. The distance from the center of the lens to the focal point is known as the focal length (denoted by f). Points that are a distance 2f from the lens are labeled 2F. Image Formation 1. A ray parallel to the principal axis is refracted through the focal point. 2. A ray through the center of the lens is not refracted. 3. A ray through the focal point is refracted parallel to the principal axis. An image is formed because light reflected from a point on the object is observed no matter where the eye is positioned. Interactive Demonstration A screen is often placed at the location of the image. The screen is NOT shown in ray diagrams. 2f 2f http://www.physicsclassroom.com/Physics-Interactives/Refraction-and-Lenses