1 / 12

LENSES

LENSES. 30.1 – Converging & Diverging Lenses. Light is refracted as it passes through glass Converging (Convex) lens – light intersects (converges) on backside, thicker in middle Diverging (Concave) lens – light spreads out (diverges) on backside, thinner in middle.

jamar
Download Presentation

LENSES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LENSES

  2. 30.1 – Converging & Diverging Lenses • Light is refracted as it passes through glass • Converging (Convex) lens – light intersects (converges) on backside, thicker in middle • Diverging (Concave) lens – light spreads out (diverges) on backside, thinner in middle

  3. Focal point = the point that parallel rays of light cross after going through lens • Principle axis – a perpendicular line going through center of lens • Focal length – the distance from center of lens to focal point

  4. 30.2 – Image Formation by a Lens Converging Lenses • Consider an object very far away (at infinity: f  ∞) • The spreading is so small, the rays are considered to be parallel • After passing through lens, they intersect at focal point on other side and produce an upside down image • Object at F  no image (forms at infinity)

  5. Between F and ∞  real, inverted • Object closer than F = virtual image – • cannot be projected onto screen, • rays of light do not intersect • Can only be seen in lens Diverging Lenses • Regardless of location of object image is: • Virtual • Upright • smaller

  6. 30.5 – Common Optical Instruments Camera • Uses lens (or lenses) to produce  real, inverted image on light sensitive film • Exposure of light is regulated by shutter/diaphragm Telescope • A second lens is used (eyepiece) as a magnifying lens to enlarge real image from first lens

  7. A third lens or prisms can be used to make image upright C0mpound Microscope • First lens (objective) produces real image (inverted) • Second: inside focal length of image producing  virtual, larger, inverted

  8. 30.6 – The Eye • Light enters through transparent cover – cornea • The amount of light allowed in through the pupil is regulated by the iris – colored part of eye • Light is focused on tissue on back of eye - retina

  9. The nerves that carry light information away (optic nerve) produce a blind spot • Muscles surrounding the lens of the eye constantly change its shape to adjust for objects close and far away • Recall: the image produced is upside down

  10. 30.7 – Some Defects in Vision Farsightedness • Eyeball is too small, the lens focuses light behind the eye • Eye cannot focus on objects too close • A converging lens is placed in front of the eye to begin the curving process

  11. Nearsightedness • Eye is too long or lens is curved too much causing focal point to be before the retina • Cannot see objects far away • Must wear diverging lenses to “slow the convergence” Astigmatism • The cornea is not uniformly curved • Causes light to focus well at certain locations on retina, but not all • Corrective lenses are specially designed

  12. 30.8 – Some Defects of Vision • Distortions of an image – abberation • Spherical abberation • Light does not focus at same location • Due to varying refraction angles at different distances from center • Corrected by: thin covering at edges or combination of lenses • Chromatic Abberation • Due to dispersion of colors as they pass through lenses • Therefore each color has its own focal point

More Related