1 Chapter 34 One of the most important uses of the basic laws governing light is the production of images. Images are critical to a variety of fields and industries ranging from entertainment, security, and medicine In this chapter we define and classify images, and then classify several basic ways in which they can be produced. Images 34-

2 The Sun is about 1.5 × m away. The time for light to travel this distance is about: A. 4.5 × sB. 8 sC. 8minD. 8 hr E. 8 yr

3 Image: a reproduction derived from light Real Image: light rays actually pass through image, really exists in space (or on a screen for example) whether you are looking or not Virtual Image: no light rays actually pass through image. Only appear to be coming from image. Image only exists when rays are traced back to perceived location of source Two Types of Images 34- object lens real image object mirror virtual image

4 Light travels faster through warm air  warmer air has smaller index of refraction than colder air  refraction of light near hot surfaces For observer in car, light appears to be coming from the road top ahead, but is really coming from sky. A Common Mirage 34- Fig. 34-1

5 Plane mirror is a flat reflecting surface. Plane Mirrors, Point Object 34- Fig Fig Identical triangles Plane Mirror: Since I is a virtual image i < 0

6 Each point source of light in the extended object is mapped to a point in the image Plane Mirrors, Extended Object 34- Fig Fig. 34-5

7 Your eye traces incoming rays straight back, and cannot know that the rays may have actually been reflected many times Plane Mirrors, Mirror Maze 34- Fig

8 Plane mirror  Concave Mirror 1. Center of Curvature C: in front at infinity  in front but closer 2. Field of view wide  smaller 3. Image i=p  | i|>p 4. Image height image height = object height  image height > object height 34- Fig Plane mirror  Convex Mirror 1. Center of Curvature C: in front at infinity  behind mirror and closer 2. Field of view wide  larger 3. Image i=p  | i|<p 4. Image height image height = object height  image height < object height Spherical Mirrors, Making a Spherical Mirror concave plane convex

9 Spherical Mirrors, Focal Points of Spherical Mirrors 34- Fig concave convex Spherical Mirror: r > 0 for concave (real focal point) r < 0 for convex (virtual focal point)

10 Start with rays leaving a point on object, where they intersect, or appear to intersect marks the corresponding point on the image. Images from Spherical Mirrors 34- Fig Real images form on the side where the object is located (side to which light is going). Virtual images form on the opposite side. Spherical Mirror: Lateral Magnification:

11 Locating Images by Drawing Rays 34- Fig A ray parallel to central axis reflects through F 2.A ray that reflects from mirror after passing through F, emerges parallel to central axis 3.A ray that reflects from mirror after passing through C, returns along itself 4.A ray that reflects from mirror after passing through c is reflected symmetrically about the central axis

12 Proof of the magnification equation 34- Fig Similar triangles (are angles same)

13 Spherical Refracting Surfaces 34- Fig Real images form on the side of a refracting surface that is opposite the object (side to which light is going). Virtual images form on the same side as the object. Spherical Refracting Surface: When object faces a convex refracting surface r is positive. When it faces a concave surface, r is negative. CAUTION: Reverse of of mirror sign convention!

Fig Converging lens Diverging lens Thin Lens: Thin Lens in air: Lens only can function if the index of the lens is different than that of its surrounding medium Thin Lenses

15 Images from Thin Lenses 34- Fig Real images form on the side of a lens that is opposite the object (side to which light is going). Virtual images form on the same side as the object.

16 Locating Images of Extended Objects by Drawing Rays 34- Fig A ray initially parallel to central axis will pass through F 2 2.A ray that initially passes through F 1, will emerge parallel to central axis 3.A ray that initially is directed toward the center of the lens will emerge from the lens with no change in its direction (the two sides of the lens at the center are almost parallel)

17 Two Lens System Let p 1 be the distance of object O from Lens 1. Use equation and/or principle rays to determine the distance to the image of Lens 1, i 1. 2.Ignore Lens 1, and use I 1 as the object O 2. If O 2 is located beyond Lens 2, then use a negative object distance p 1. Determine i 2 using the equation and/or principle rays to locate the final image I 2. Lens 1 Lens 2 p1p1 O I1I1 i1i1 O2O2 p2p2 I2I2 i2i2

18 The time for a radar signal to travel to the Moon and back, a one-way distance of about 3.8 × 10 8 m, is: A. 1.3 sB. 2.5 sC. 8 sD. 8min E. 1 × 10 6 s Radio waves of wavelength 3 cm have a frequency of: A. 1MHzB. 9MHzC. 100MHzD. 10, 000MHzE. 900MHz The light intensity 10m from a point source is 1000W/m 2. The intensity 100m from the same source is: A. 1000W/m 2 B. 100W/m 2 C. 10W/m 2 D. 1W/m 2 E. 0.1W/m 2

19 Light of uniform intensity shines perpendicularly on a totally absorbing surface, fully illuminating the surface. If the area of the surface is decreased: A. the radiation pressure increases and the radiation force increases B. the radiation pressure increases and the radiation force decreases C. the radiation pressure stays the same and the radiation force increases D. the radiation pressure stays the same and the radiation force decreases E. the radiation pressure decreases and the radiation force decreases

20 A clear sheet of polaroid is placed on top of a similar sheet so that their polarizing axes make an angle of 30◦ with each other. The ratio of the intensity of emerging light to incident unpolarized light is: A. 1/4B. 1/3C. 1/2D. 3 /4E. 3 /8

21 Optical Instruments, Simple Magnifying Lens 34- Fig Can make an object appear larger (greater angular magnification) by simply bringing it closer to your eye. However, the eye cannot focus on objects closer that the near point p n ~25 cm  BIG & BLURRY IMAGE A simple magnifying lens allows the object to be placed close by making a large virtual image that is far away. Simple Magnifier: Object at F 1

Fig Optical Instruments, Compound Microscope I close to F 1 ’ O close to F 1 Mag. Lens

23 Optical Instruments, Refracting Telescope 34- Fig I close to F 2 and F 1 ’ Mag. Lens

24 Three Proofs, The Spherical Mirror Formula 34- Fig

25 Three Proofs, The Refracting Surface Formula 34- Fig

Fig Three Proofs, The Thin Lens Formulas