Today s Topic: Ray Diagrams Intro to & Converging

Transcription

1 Today s Topic: Ray Diagrams Intro to & Converging Learning Goal: Students will be able to describe the resulting image of light once it passes through a converging lens. What is a focal point? What happens at the focal point of a converging lens? What happens at the focal point of a diverging lens?

2 Homework Complete the Snell s Law Worksheet (One Day Late) Complete The Law of Reflection packet (our Days Late)

3 Upcoming Test Your last test will take place on Thursday, June 4 th (a week from yesterday). Topics covered will include: Color The Law of Reflection Refraction Snell s Law Ray Diagrams (Converging & Diverging)

4 Recap A converging lens, or a convex lens, is thicker in the middle, and causes rays of light that are initially parallel to CONVERGE at a single point called the focal point. ocal point

5 Converging Lens Principal Axis

6 Converging Lens Principal Axis Light rays that come in parallel to the principle axis converge at the focal point.

7 Recap A diverging lens, or a concave lens, is thinner in the middle, causing the rays of light to appear to originate from a single point.

8 Diverging Lens Principal Axis Light rays that come in parallel to the principle axis diverge from the focal point.

9 Images All visible objects emit or reflect light rays in all directions.

10 Images Our eyes detect these light rays.

11 Images We see images when light rays converge in our eyes.

12 Mirrors and Lenses It is possible to see images in mirrors and lenses as well. image object

13 Reflecting Light Light from an object bounces off of a mirror, obey the law of reflection, and our eyes see these reflections. However, these rays almost appear to be coming from behind the mirror. The object we see behind the mirror is called an image.

14 Reflecting Light However, things start to get a little strange once we bend the mirror. By bending the mirror, the image can appear in a different location or different size.

15 Ray Diagrams By constructing a ray diagram, we can determine where the image is located, and what it will look like. A ray diagram is a diagram showing rays that can be drawn to determine the size and location of an image formed by a mirror or lens.

16 Ray Diagrams A ray diagram looks something like this: Let s take a step back and see this.

17 Key eatures of a Lens Like a wave, lenses have some key features we need to learn. The principal axis of a lens is the line joining the centers of curvature of its surfaces.

18 Key eatures of a Lens The focal point (for a converging lens) is the point where a beam of light parallel to the principal axis converges.

19 Key eatures of a Lens The focal length is the distance between the center of the lens and its focal point.

20 Key eatures of a Lens This is a less scary example of a completed ray diagram. Let s learn the rules in constructing one of these things. We re only going to focus on converging lenses today.

21 Ray Tracing Rules To create a ray diagram, you will need to draw two of the three following rays: Ray 1: A ray parallel to the principal axis that passes through the focal point on the opposite side

22 Ray Tracing Rules Ray 2: A ray that passes through the center of the lens that is undeflected.

23 Ray Tracing Rules Ray 3: A ray that passes through the focal point in front of the lens that emerges parallel to the principal axis after refracted by the lens.

24 Putting It All Together Draw the image where the rays intersect! object image Converging Lens

25 Image Descriptions Images can be described with three classifications: A real image is an image where the light from the object actually converges to form an image which can be seen on a screen. A virtual image is an image that appears to be in a location where light does not really reach.

26 Mirrors and security mirrors produce virtual images the light does not really reach behind the glass, it only appears to do so. Lens Effects The projector is producing a real image it can be seen on a screen.

27 Image Descriptions Images can be described with three classifications: An upright image has the same vertical direction as the object. An inverted image is flipped upsidedown. Magnification: The image is larger (than the object), smaller, or the same size.

28 More Examples Describe the image formed above. Real Inverted Same Size

29 Describe the image formed above. Real Inverted Larger By moving the object closer to the lens, the image is now magnified. More Examples

30 Let s bring the object even closer! Uh oh. In this case the rays are diverging they do not intersect on that side of the lens. More Examples this distance is increasing

31 More Examples But if we extend the rays backwards The image will form here. This is a virtual image. This configuration is how a magnifying glass works.