Physics Lenses & Ray Diagrams

Answer on a Warm Up Slip 1. What portion of the EM Spectrum can pass through people? How is this helpful? 2. What media does light require? 3. What is the relationship of frequency and wavelength? Is this useful when discussing EM Radiation? 4. What determines how fast a wave travels in a vacuum?

Answer on a Warm Up Slip The bend of a straw is an example of ________. Draw the diffraction gradient that blocks the most light. Which wave is brightest at t=.75s Dimmest at t=.75s Smallest period Greatest period has a Period 2x the other Has a frequency ½ the other Travels the fastest

Review

Review

Answer on a Warm Up Slip What portion of the EM Spectrum can pass through people? Any with a high frequency How is this helpful? Xrays pass through soft tissue and radiate the film behind the person What media does light require? None What is the relationship of frequency and wavelength? Inverse Is this useful when discussing EM Radiation? Classification What determines how fast a wave travels in a vacuum? High frequency, low wavelength

Thin lenses Mirrors reflect, Lenses Refract (bend)!!! Those of you with glasses or contacts are thankful for lenses, because they redirect light rays to help you see better (shine light on your retina). Lenses: 1. Converging Lens – converge light to a single point (Focal Point) 2. Diverging Lens – diverge light away from a single point. Also called Convex and Concave We will only study Converging (Convex) Lenses

Converging Lens How to find the focal point? The focal point is defined as the intersection of parallel rays (for example, the sun’s rays form a hotspot). These parallel rays come from an infinite object distance. Light rays can go through a lens from either side, (because the convergent lense is the same on both sides) therefore Converging Lenses have TWO focal points.

Converging Lens In physics, we use lenses and objects to produce an image. Where is the image? Two methods to find an image: 1. Ray Diagram 2. Equations (next PowerPoint) Done correctly, both give you the right answer!

Double Convex Lens = Converges Light to a single point Ray Diagrams Double Convex Lens = Converges Light to a single point object Focal point 2F F axis

Ray Diagrams Holt, 571 Light travels in all directions, however we are not going to draw every single light ray, only 3 Principle Rays. “Rules” from top of image 1. A parallel (to the axis) ray refracts through the focal point, F, on the other side. In II (parallel), out F 2. A ray that passes through the first focal point, F, refracts parallel on the other side. In F, out ll (parallel) 3. A ray that passes through the center of the lens, C, and continues on the original path. through center

Ray 1 Straight line from the top of the object: In ll, out F 2F F

Ray 2 Straight line from the top of the object: In F, out ll 2F F

Ray 3 Straight line from the top of the object: Through center (where lens bisects axis) 2F F

Ray Diagrams Draw arrowheads on each to show the path of the rays. All rays will pass through the lens and converge on a single point on the other side according to the following rules

Ray 1 Straight line from the top of the object: In ll, out F 2F 2F F F

Ray 2 Straight line from the top of the object: In F, out ll 2F F

Ray 3 Straight line from the top of the object: Through center 2F F

Ray Diagrams Draw arrowheads on each to show the path of the rays. The point at which all of the rays converge indicates where the top of the object is viewed when looking through a converging lens object apparent object Purpose: Show the location, size, orientation, and type of image formed by a double convex lens = converging lens.

Ray Diagrams Compare before and after the lens for each light ray object Compare be the orientation of the object. Compare the angles of the Ray 1 to Ray 3 Compare all of the angles before to all of the angles after the lenses. What relationships do you see. ____________________________________________________________________________________________________________________

Write your own rules Write a rule in your own words for each ray from beginning to end. Ray 1 Ray 2 Ray 3

Ray Diagrams Where you put the object determines a lot about the image. Images can be described with three classifications: Real: Light really passes through the intersection. Virtual: Light does not pass through the intersection – you have to pretend it does. Upright – Same vertical direction as object. Inverted – Opposite vertical direction as object. Magnification: Larger (than object), smaller (than object), or same size (as the object).

New Terms Object Distance (do): The distance measured from the lens (x=0) to the object’s location. Image Distance (di): The distance measured from the lens (x=0) to the image’s location. Typically, images from converging lenses are on the opposite side as the object. This is what light really wants to do—pass through a lens. Therefore, If di is on the opposite side of lens = positive (+di) If di is on the same side of lens = negative (- di) * Only one scenario for this!

New Terms Object Height (ho): “how tall” the object is. Upright = +ho Inverted = -ho Image Height (hi): “how tall” the image is (relative to the object). Upright = +hi Inverted = -hi At this point, we will look at the heights to determine the relative magnification.

Example 1 Is this lens Convex or Concave? Draw the Diagram Use a Ruler! 2F F 2F 2F

Example 1 Is this lens Convex or Concave? Draw the Diagram Use a Ruler! Lines cross = real image (if lines don’t cross = imaginary image Apparent object is same size as original = no magnification 2F 2F Apparent object is under the axis = inverted

Example 1 Is this lens Convex or Concave? Draw the Diagram Use a Ruler! 2F 2F

Example 2