Sasha Bernard 5A Physics PowerPoint #2 Mr. Davis Sections of the syllabus

ACTION OF LENSES

SOME DEFINITIONS  Principal axis - a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted; "in a normal eye the optic axis is the direction in which objects are seen most distinctly"  Principal Focus – A focal point  Focal Length - The distance from the surface of a lens or mirror to its focal point.  Focal Plane -The plane, perpendicular to the optical axis of the lens, in which images of points in the object field of the lens are focused.  Magnification – The act of magnifying; an enlarged representation, image, or model.

REAL AND VIRTUAL IMAGES Real images are those where light actually converges, whereas virtual images are locations from where light appears to have converged. Real images occur when objects are placed outside the focal length of a converging lens or outside the focal length of a converging mirror.

REAL AND VIRTUAL IMAGES 2

RELATIONSHIP AMONG IMAGE DISTANCE, OBJECT DISTANCE AND MAGNIFICATION Magnification = image size/object size

EXPERIMENTALLY DETERMINING THE FOCAL LENGTH OF A LENS 1. Measure the diameter of the quarter and record below. 2. Place your quarter (object) and lens so the diameter of the image the quarter on the screen is less then 1.5 cm. Make sure that the image is brought into sharp focus. 3. Measure the distance between the object and the lens. Record the value in the table below. 4. Measure the distance between the lens and the screen. Record the value in the table below.

RAY DIAGRAMS TO SHOW HOW A SINGLE LENS IS USED  Magnifying Glass -

HOW THE EYE FORMS AN IMAGE Our eyes have a small window at the front through which the light can enter. It is called the pupil. The pupil appears black because it is dark inside our eye. At the back of our eye is a sensitive sheet of nerves called the retina. These nerves can detect light when it strikes the retina. Our eye forms an image on the retina. This image is like a small picture of what you are looking at. If you are looking at a house, then an image of the house is focused by the lens of the eye onto the retina. The nerves in the retina send messages about the image to the brain, and your brain enables you to interpret what you are looking at. Our eyes can detect images only because of the light that enters into them. If you close your eyes, the light cannot enter them, and you can detect nothing but darkness.

DIAGRAM OF THE EYE