 Get out notes and practice from yesterday  Pick up ruler and finish practice from yesterday

A 1.5 cm object is placed 6.0 cm from a double convex lens, which has a focal length of 1.5 cm.

A 1.5 cm object is placed 3.0 cm from a convex lens, which has a focal length of 1.5 cm.

 A lens is a piece of transparent material, such as glass or plastic, that is used to bend light and produce an image.  When light passes through a lens, refraction occurs.

 A convex lens is thicker at the center than at the edges.  A convex lens is a converging lens because it refracts parallel light rays of light so that they meet at a focal point.  A concave lens is a thinner in the center than at the edges.  A concave lens is a diverging lens because rays passing through the lens spread out.

Lenses Converging Lens Diverging Lens F F f f

 Lenses consist of two faces  Each face of the lens can be either curved or flat.  A lens consisting of two curved surfaces will have two focal points.

Double Convex Lens

 Virtual images formed by lenses are on the same side of the lens as the object.  Virtual images are always upright.  Real images formed by lenses are on the opposite side of the lens from the object.  Real images are always inverted.

 Concave lenses produce virtual, upright, reduced images.

 Convex lenses produce either real or virtual images.  If the image is virtual, it will also be upright and enlarged.  If the image is real, it can be enlarged, reduced, or the same size as the object.

 The lens is more optically dense, so light slows down.  When light passes from air through a lens, it bends toward the normal.

1. Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens. 2. Any incident ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.

 An incident ray that passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.

1. The ray that travels parallel to the principal axis on the way to the lens will refract and travel in a direction such that its extension passes through the focal point on the object's side of the lens. 2. Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.

 An incident ray that passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.  This is true for both concave and convex lenses.

Ray Tracing for Lenses Light passes through a lens There is a focal point on both sides of a lens Converging Lens: Ray #1: Parallel to the axis Refracts through F Ray #2: Through F Refracts parallel to axis Ray #3: Through Center of lens undeflected

For a lens, a real image is on the opposite side as the object The Thin Lens Equation These equations also work on lenses: The Magnification Equation But the variables are defined slightly differently now because………. For a mirror, a real image was on the same side as the object

 The eye act as a lens.  The cornea is the transparent covering that protects the eye.  The cornea is also the part of the eye that refracts light.  The iris is the colored part of the eye surrounding the pupil and regulates the amount of light that enters the eye.

 The pupil is the opening through which light enters.  The pupil appears black because light is entering but not leaving. All light entering the eye is absorbed.  The eye lens is a crystalline lens. Muscles change the shape of the lens which changes its focal length.

 The retina is the inner surface of the eye.  The retina contains rods and cones that detect the intensity and frequency of incoming light.  The rods and cones send nerve impulses to the brain along the optic nerve.

 The eye can change the focal length through a process called accommodation.  This process occurs automatically and allows us to see objects nearby and far away.  Based on the focal length of our eye (approximately 1.8 cm) images formed on our retina are reduced, inverted, and real.  An image is produced by the cornea lens system on the retina.  The brain interprets the signal from the retina and we see an object as right side up.  s&view=detail&mid=1D185809FDBF88EEF4941D185809F DBF88EEF494&first=0&FORM=NVPFVR s&view=detail&mid=1D185809FDBF88EEF4941D185809F DBF88EEF494&first=0&FORM=NVPFVR

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 Far-sightedness (hyperopia)- allows objects far away to be seen clearly, but objects close up cannot be focused clearly.  This occurs because the focal length is longer than the distance from the lens to the retina.  The image forms behind the retina.

 A convex lens is used to correct the problem because it is a converging lens.  The corrective lens causes light to refract before it reaches the eye, decreasing the image distance, and focusing the image on the retina.  This condition normally occurs as you age because the muscles in your eye become rigid.

 Near-sightedness (myopia) occurs when nearby objects can be seen clearly but far away objects are not focused clearly.  Occurs because the focal length is shorter than the distance from the lens to the retina.  Images form in front of the retina.  ain/nearsighted.shtml ain/nearsighted.shtml

 A concave lens is used to correct the problem because it is a diverging lens.  The corrective lens causes light to diverge before it hits the eye lens. (The light is then converged by the cornea and eye lens)  More common in young people due to a bulging cornea.  ain/nearsighted.shtml ain/nearsighted.shtml

 Astigmatism occurs when the eyeball is not spherical.  The result is that vertical lines of images can focus while horizontal lines are not.  Eyeglasses having a non-spherical shape correct the problem.

 Microscopes allow the eye to see extremely small objects  Most microscopes use two convex lenses  an objective lens with a short focal length  an eyepiece or ocular lens (magnifies the image)  Telescopes allow the eye to see very distant objects  Telescopes use two convex lenses  Objective lens has a long focal length  The eyepiece lens has a short focal length  Allows more light to enter the eye 

 Lenses have 2 focal points  Convex lenses form the same type of images as concave mirrors  Convex lenses are converging  Concave lenses form the same type of images as convex mirrors  Concave lenses are diverging

 Form on the same side of the lens as the object are virtual  Have a negative di  Have a positive hi (upright images)

 Images that form on the opposite side of the lens as the object are real  Have positive di  Have a negative hi (inverted images)

 For each problem below, draw the ray diagram for the lens.  Draw each diagram to scale and include the principal axis, lens, f, and 2f.  Measure the location of the image and the height of the image.  Calculate these values and compare with the measured values.

1. A 2.0 cm object is placed 10.0 cm from a double convex lens, which has a focal length of 3.0 cm. 2. A 2.0 cm object is placed 6.0 cm from a double convex lens, which has a focal length of 3.0 cm.