Unit 8: Light and Optics Chapter 22: Optics 22.3 Mirrors, Lenses, and Images REVIEW/KEY

SWBAT… explain how images are created. OBJECTIVE 4/30 and 5/1 SWBAT… explain how images are created.

Mirrors, Lenses, and Images (#2) Objects are real physical things that give off or reflect light rays. Images are “pictures” of objects that are formed in space where light rays meet. (#1)

Virtual images Because the light rays do not actually meet, a virtual image cannot be projected onto a screen or on film. Virtual images are illusions created by your eye and brain. Example - photograph (#3)

Objects and Images (#4) The arrow on the graph paper is an object because it is a physical source of reflected light. The virtual image in a flat mirror is created by the eye and brain .

Virtual images A ray diagram shows the arrows are together at an object, split at the mirror, and are appear together again to form an image. (#5)

Objects and Images (#6) The image in the mirror is called a virtual image. These images are illusions created by your brain and eye, so you cannot project them onto a screen.

Lenses (#7) An ordinary lens is a polished, transparent disc, usually made of glass. It is made of transparent material with an index of refraction different from air. The optical axis usually goes through the center of the lens.

Mirrors, Lenses, and Images (#8) Light rays that enter a converging lens parallel to its axis bend to meet at a point called the focal point. The distance from the center of the lens to the focal point is called the focal length.

Converging lenses (#9) For a converging lens, the first surface (air to glass) bends light rays toward the normal.

A diverging lens bends the rays outward, away from the focal point. Diverging lenses (#10) A diverging lens bends the rays outward, away from the focal point.

Drawing ray diagrams (#11) A ray diagram is the best way to understand what type of image is formed by a lens, and whether the image is magnified or inverted. These three rays follow the rules for how light rays are bent by the lens: A light ray passing through the center of the lens is not deflected at all (A). A light ray parallel to the axis passes through the far focal point (B). A light ray passing through the near focal point emerges parallel to the axis (C).

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The image formed by a lens (#12) A converging lens can also form a real image. In a real image, light rays from the object actually come back together at the focus

Movie Theater (#13) The lens in a movie projector also makes an upside-down image. To make the image right side up, the film is put in the projector upside down!

Magnification (#14) The magnification of an image is the ratio of the size of the image divided by the size of the object. A lens with a magnification of 4 creates an image that appears four times larger than the real-life object.

The image will be smaller and upside down. Magnification (#15) What happens if you hold a magnifying glass farther than one focal length away from the object that you are trying to observe? The image will be smaller and upside down.

The Telescope (#16) When people think of a telescope, most of them think of a refracting telescope. It has two converging lenses with different focal lengths. The lens with the longest focal length is called the objective and the shorter-focal-length lens is the eyepiece.

The reflecting telescope (#16) Because high-quality, large lenses are difficult to make, reflecting telescopes use a concave mirror instead of one lens. The diagram shows a reflecting telescope, much like the one used by the Hubble Space Telescope.

Optical systems (#17) Optical systems are built from lenses, mirrors, and prisms. Optical systems do two things: collects light rays changes/processes the light rays to form an image. A camera is an optical system that collects light to record an image.

Pin-hole camera (18) A simple optical system can be made with a pinhole in a box. The image inside the box forms because light rays that reach a point on the box surface are restricted by the pinhole to come from only a pinhole-sized point on the object.

Pin-hole camera (#18) The larger the lens, the brighter the image. This is because a larger lens collects more light rays. Multiple lenses are useful because they allow an optical system to change the size of an image. A telephoto camera lens uses two or more lenses that move relative to one another.

Recording images (#19) There are two basic techniques for recording images. Film records an image by using special inks that respond to light leading to a negative. A digital camera uses a tiny sensor called a CCD.