Chapter 11.pdf

Night vision goggles use lenses to focus light onto a device called animage intensifier. Inside the intensifier, the light energy releases astream of particles. These particles then hit a phosphor-coated screen.The phosphors glow when the particles strike them. The personwearing the goggles sees a glowing green image (Figure 11.47).Figure 11.47 The image intensifier of night goggles amplifies the particles before they hit thescreen. The image appears as shades of green.D21 Quick LabObserving LensesPurposeTo observe how concave and convex lenses affectlightMaterials & Equipment• convex lens (bulgesout)• concave lens (middle isthinner than the edges)• light source, such as acandle• screen, such as apiece of paper• candle holder, such assand and a metal trayCAUTION: If an open flame is used, it must be secured sothat it cannot fall over. Keep all combustible materialsaway from open flames. Tie back long hair before usingan open flame.Procedure1. Look though each lens at the printed text in thisstudent book. Record your observations.2. Look through both lenses at some printed text.Record your observations.3. Try to use each of the lenses to project a candleflame or light onto a screen or piece of paper.Record your observations.Questions4. Which single lens would be most useful as amagnifying glass?5. How should the convex and concave lenses bearranged to make a distant object appear closer?6. What arrangement of lenses is most effective inprojecting the image of a light source onto apiece of paper?Ray diagrams model the behaviour of light in mirrors and lenses.449