Refraction and Lenses

Transcription

1 Reraction and Lenses

2 The most common application o reraction in science and technology is lenses. The kind o lenses we typically think o are made o glass or plastic. The basic rules o reraction still apply but due to the curved surace o the lenses, they create images.

3 real image inverted image ormed on the opposite side o lens as object ormed where light rays actually converge ( cross ) visible on the screen ( projectable ) virtual image upright image ormed on the same side o a lens as object ormed where light rays appear to cross not visible on a screen (not projectable)

4 REAL IMAGE FORMATION BY LENSES

5 VIRTUAL IMAGE FORMATION BY LENSES

6 The two main types o lenses are convex and concave lenses. The ocal length () o a lens depends on its shape and its index o reraction.

7 A diverging (concave) lens is thin in the center and thick at the edges. A converging (convex) lens is thick in the center and thin at the edges.

8 Concave Lenses = Diverging Lenses spread out light rays. or nearsightedness (myopia) orms virtual images only always upright and reduced aka reducing lenses

9 Convex Lenses = Converging Lenses bring light rays to a ocus. or arsightedness (hyperopia) orm virtual images (upright & enlarged) aka magniying Lenses Forms real images

10

11 CONVEX LENSES Where is the object when the image is the same size? Where is the object when there is no image?

12 The eye contains a convex lens. This lens ocuses images on the back wall o the eye known as the retina.

13 VISION PROBLEMS: MYOPIA is when image is ormed in ront o retina and is also known as nearsightedness and is corrected with a concave lens

14 VISION PROBLEMS: HYPEROPIA is when image is ormed behind the retina and is also known as arsightedness and is corrected with a convex lens

15 VISION PROBLEMS: ASTIGMATISM is when the eye is shaped like a ootball rather than the normal eye that has a round shape similar to basketball. It causes certain amounts o distortion or pitched images because o the uneven bending o light rays entering the eye.

16 Parts o a Lens All lenses have a ocal point (). In a convex lens, parallel light rays all come together at a single point called the ocal point. In a concave lens, parallel light rays are spread apart but i they are traced backwards, the reracted rays appear to have come rom a single point called the ocal point. Real Virtual

17 Lens Equation (1/) = (1/d o ) + (1/d i ) = ocal length d o = object distance d i = image distance

18 Lens Magniication Equation M = -(d i / d o ) = (h i / h o ) M = magniication d i = image distance d o = object distance h i = image height h o = object height

19 d i d o h i h o M Lens Sign Conventions + or Convex lenses - or Concave Lenses + or images on the opposite side o the lens (real) - or images on the same side (virtual) + always + i upright image - i inverted image + always + i virtual - i real image Magnitude o magniication <1 i smaller =1 i same size >1 i larger

20 Ex. 7 Camera lenses are described in terms o their ocal length. A 50 mm lens has a ocal length o 50 mm. Do cameras use converging or diverging lenses? What does d i represent? a. Where is the image (rom the lens) o the above camera when it is ocused on an object 3.0 meters away? b. What is the magniication o the image? c. I the object is 1.5 m tall, what is the height o the image? d. What is the di i the object is 6 m away? As the do increased, what happened to the di?

21 Rules or Locating Reracted Images 1. Start at top o object. Light rays that travel through the center o the lens (where the principle axis intersects the midline) are not reracted and continues along the same path. 2. Start at top o object. Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

22 Images ormed by Convex lenses

23 Locating images in convex lenses

24 Convex Lenses with the Object located beyond 2

25 Convex Lens Object located beyond C C C Light rays that travel through the center o the lens are not reracted and continue along the same path.

26 Convex Lens Object located beyond Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

27 Convex Lens Object located beyond 2 2 Image: Real Inverted Smaller 2 The image is located where the reracted light rays intersect

28 Convex Lenses with the Object located at 2

29 Convex Lens Object located at Light rays that travel through the center o the lens are not reracted and continue along the same path.

30 Convex Lens Object located at Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

31 Convex Lens Object located at 2 2 Image: 2 Real Inverted Same Size The image is located where the reracted light rays intersect

32 Convex Lenses with the Object located between and 2

33 Convex Lens Object located between and Light rays that travel through the center o the lens are not reracted and continue along the same path.

34 Convex Lens Object located between and Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

35 Convex Lens Object located between and 2 2 Image: 2 Real Inverted Larger Beyond 2 The image is located where the reracted light rays intersect

36 Convex Lenses with the Object located at

37 Convex Lens Object located at 2 2 Light rays that travel through the center o the lens are not reracted and continue along the same path.

38 Convex Lens Object located at 2 2 Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

39 All reracted light rays are parallel and do not cross Convex Lens Object located at 2 2 No image is ormed.

40 Convex Lenses with the Object located between and the lens

41 Convex Lens Object located between and the lens 2 2 Light rays that travel through the center o the lens are not reracted and continue along the same path.

42 Convex Lens Object located between and the lens 2 2 Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

43 Convex Lens Object located between and the lens 2 2 These to reracted rays do not cross to the right o the lens so we have to project them back behind the lens.

44 Convex Lens Image: 2 Virtual Upright Larger Further away Object located between and the lens 2 The image is located at the point which the reracted rays APPEAR to have crossed behind the lens

45 Images ormed by concave lenses

46 Locating images in concave lenses

47 Concave Lenses with the Object located anywhere

48 Concave Lens Object located anywhere 2 2 Light rays that travel through the center o the lens are not reracted and continue along the same path.

49 Concave Lens Object located anywhere 2 2 Light rays that travel parallel to the principle axis, strike the lens, and are reracted through the ocal point ().

50 Concave Lens Object located anywhere Image: Virtual 2 2 Upright Smaller Between and the lens The image is located where the reracted light rays appear to have intersected

51 Someone who is nearsighted can see near objects more clearly than ar objects. The retina is too ar rom the lens and the eye muscles are unable to make the lens thin enough to compensate or this. Diverging glass lenses are used to extend the eective ocal length o the eye lens.

52 Someone who is arsighted can see ar objects more clearly than near objects. The retina is now too close to the lens. The lens would have to be considerable thickened to make up or this. A converging glass lens is used to shorten the eective ocal length o the eye lens. Today s corrective lenses are careully ground to help the individual eye but cruder lenses or many purposes were made or 300 years beore the reractive behavior o light was ully understood.