Unit #3 - Optics. Activity: D21 Observing Lenses (pg. 449) Lenses Lenses

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1 ist10_ch11.qxd Unit #3 - Optics 11.3 Lenses 7/22/09 3:53 PM Page 449 Night vision goggles use lenses to ocus light onto a device called an image intensiier. Inside the intensiier, the light energy releases a stream o particles. These particles then hit a phosphor-coated screen. The phosphors glow when the particles strike them. The person wearing the goggles sees a glowing green image (igure 11.47). Activity: D21 Observing Lenses (pg. 449) igure The image intensiier o night goggles ampliies the particles beore they hit the screen. The image appears as shades o green. D21 Quick Lab Observing Lenses Purpose Procedure To observe how concave and convex lenses aect light 1. Look though each lens at the printed text in this student book. Record your observations. 2. Look through both lenses at some printed text. Record your observations. Materials & Equipment convex lens (bulges out) screen, such as a piece o paper concave lens (middle is thinner than the edges) candle holder, such as sand and a metal tray 3. Try to use each o the lenses to project a candle lame or light onto a screen or piece o paper. Record your observations. Questions light source, such as a candle 4. Which single lens would be most useul as a magniying glass? CAUTION: I an open lame is used, it must be secured so that it cannot all over. Keep all combustible materials away rom open lames. Tie back long hair beore using an open lame. 5. How should the convex and concave lenses be arranged to make a distant object appear closer? 6. What arrangement o lenses is most eective in projecting the image o a light source onto a piece o paper? Ray diagrams model the behaviour o light in mirrors and lenses. Lenses curved transparent material that is smooth and regularly shaped transparent glass or very hard plastic thin lens strong, hard, polished rays converge or diverge can magniy the image image produced by a thin lens can be real or virtual, inverted or upright, larger or smaller. thickness is slight compared to its ocal length 449

2 Two Types (a) axis o symmetry converging lenses (thickest in the middle) diverging lenses (thinnest in the middle) Deine: (pg. 450) principle axis axis o symmetry principal axis ocal point (x 2) () ocal length () principal axis axis o symmetry igure Concave Lenses aka: diverging lens light is reracted away rom the principle axis rays will never meet on other side Image: smaller, upright, virtual (a) Uses eyeglasses have one convex surace and one concave surace telescopes and binoculars use concave lenses to improve the detail Diagrams Rules or Ray Diagrams ray parallel to PA extends rom ocal point ray travelling through centre, in not reracted (stays straight) Image is located at ray intersection object ray 1 ray 2 image

3 Homework Convex Lenses Read Draw a diverging lens with a ocal point o 4 cm, and draw image at these situations: - An Object which is 2 cm tall and 8 cm rom the axis o symmetry - An Object 4 cm tall and 2 cm rom the A o S aka: converging lens light is reracted toward the principle axis Activity: D24 - ocal Length (pg. 459) Read steps 2-9 Object outside P image is real; inverted Object inside P image is virtual; upright diaphragm ocussing ring ilm spool Uses aperture ilm camera projectors object lens image (on ilm) shutter magniying glass d o d i igure The parts o a simple camera that uses ilm

4 Diagrams Rules or Ray Diagrams ray parallel to PA travels through ray travelling through centre, in not reracted (stays straight) ray that goes through, stays parallel Image is located at ray intersection object ray 1 ray 2 image igure Convex lens ray diagram Activity: D26 - Identiying the Properties o Images Thin Lens Equation Handout pg 461 Qu # 10 ocal Length () distance o object (do) distance o image (di) 1 = 1 do + 1 di Remember that: A concave lens has a negative ocal length and a negative distance to the image. A convex lens has a positive ocal length and either a positive or negative distance to the image, depending where the object is placed. A convex lens has a ocal length o 60.0 cm. A candle is placed 50 cm rom the lens. What type o image is ormed, and how ar is the image rom the lens? The image distance di is positive i the image is real and negative i the image is virtual.

5 Example: A convex lens o a magniying glass is held 2.00 cm above a page to magniy the print. I the image produced by the lens is 3.60 cm away and virtual, what is the ocal length o the magniying glass? A camera with a 200 mm lens makes a real image o a bird on ilm. The ilm is located 201 mm behind the lens. Determine the distance rom the lens to the bird. Activity: D26 - Identiying the Properties o Images Homework Handout pg 461 Qu # 10 Read pg Qu # 10, 11, 12 pg Qu #1-3 pg Qu #1 rom each group