Image formation Ch. 36

Reflection Law

Images Formed by Mirrors 1. Images Formed by Flat Mirrors 2. Images Formed by Spherical Mirrors a- Concave Mirrors b- Convex Mirrors Images Formed by Thin Lenses

Images are classified as: * real image is formed when light rays pass through and diverge from the image point. * virtual image is formed when the light rays do not pass through the image point but only appear to diverge from that point.

1. Images Formed by Flat Mirrors, cont. p :object distance q : image distance Point [ I ] is called the image of the object at [O]

Flat mirror has the following properties: 1. The image is as far behind the mirror as the object is in front. p = q 2. The image is unmagnified, virtual, and upright. (By upright we mean that, if the object arrow points upward so does the image arrow.) 3. The image has front back reversal.

Note: a flat mirror produces an image that has an apparent left right reversal. You can see this reversal by standing in front of a mirror and raising your right hand.

Magicians Optical

2. Images Formed by Spherical Mirrors Spherical Mirrors are classified as: 1- Concave Mirrors that is, one silvered so that light is reflected from the inner, concave surface. This is sometimes called a converging mirror.

2. Images Formed by Spherical Mirrors Spherical Mirrors are classified as: 2- Convex Mirrors that is, one silvered so that light is reflected from the outer, convex surface. This is sometimes called a diverging mirror.

The component of the Spherical Mirrors is : R: the mirror radius of curvature C: center of curvature V : the center of the mirror. The line through C and V is called the principal axis of the mirror.

- Other component of the Spherical Mirrors.V F : the focal point, which depends only on the curvature of the mirror and not on the material from which the mirror is made. The line through F and V is called the focal length f, which represents the image distance that corresponds to an infinite object distance.

Ray Diagrams for Mirrors Ray 1 is drawn from the top of the object parallel to the principal axis and is reflected through the focal point F. Ray 2 is drawn from the top of the object through the focal point and is reflected parallel to the principal axis. Ray 3 is drawn from the top of the object through the center of curvature C and is reflected back on itself.

2.1 Images Formed by Concave Mirrors

2.2 Images Formed by Convex Mirrors

Quick Quiz: You wish to start a fire by reflecting sunlight from a mirror onto some paper under a pile of wood. Which would be the best choice for the type of mirror? (a) flat (b) concave (c) convex

Quick Quiz Based on the appearance of this image, you would conclude that (a) the mirror is concave and the image is real. (b) the mirror is concave and the image is virtual. (c) The mirror is convex and the image is real. (d) the mirror is convex and the image is virtual. The Hubble Space Telescope primary mirror.

Refraction

3. Images Formed by Thin Lenses Lenses are commonly used to form images by refraction in optical instruments such as cameras, telescopes, and microscopes. F 2 F 1

Shapes of Lens Converging lens Diverging lens

Ray Diagrams for a converging lens Ray 1 is drawn parallel to the principal axis. After being refracted by the lens, this ray passes through the focal point on the back side of the lens. Ray 2 is drawn through the center of the lens and continues in a straight line. Ray 3 is drawn through the focal point on the front side of the lens (or as if coming from the focal point if p < f ) and emerges from the lens parallel to the principal axis.

Ray Diagrams for a converging lens

Ray Diagrams for a diverging lens Ray 1 is drawn parallel to the principal axis. After being refracted by the lens, this ray emerges directed away from the focal point on the front side of the lens. Ray 2 is drawn through the center of the lens and continues in a straight line. Ray 3 is drawn in the direction toward the focal point on the back side of the lens and emerges from the lens parallel to the principal axis.

Ray Diagrams for a diverging lens

Mirror & Lens Equation Were p is the object distance. q is the image distance. f is the focal length.

Magnification Equation )M( of an image for Mirror & Lens Where h is image height h is object height For plane Mirrors M = 1

Sign Conventions for Mirrors & lenses Quantity Positive When Negative When Image location (q) Focal length (f ) Magnification (M) real image Converging Mirror \ lenses Image is upright virtual image Diverging Mirror \ lenses Image is inverted

Example An automobile rearview mirror shows an image of a truck located 10.0 m from the mirror. The focal length of the mirror is 20.60 m. (A) Find the position of the image of the truck. (B) Find the magnification of the image.

Example A spherical mirror has a focal length of 110.0 cm. (a) Locate and describe the image for an object distance of 25.0 cm. (b) Locate and describe the image for an object distance of 10.0 cm. (c) Locate and describe the image for an object distance of 5.00 cm.

Example: Images Formed by a Converging Lens A converging lens of focal length 10.0 cm forms images of objects placed (A) 30.0 cm, (B) 10.0 cm, and (C) 5.00 cm from the lens. In each case, construct a ray diagram, find the image distance and describe the image.