Lenses PDF

Lenses Lenses - objects that cause rays of light to converge through refraction. A review of refraction ➔ When light passes into a different medium, it is refracted at the boundary. ➔ When passing into a denser medium, the ray is refracted toward the normal. ➔ T...

Lenses Lenses - objects that cause rays of light to converge through refraction. A review of refraction ➔ When light passes into a different medium, it is refracted at the boundary. ➔ When passing into a denser medium, the ray is refracted toward the normal. ➔ The ray refracts away from the normal at the boundary as it passes to a less dense medium. There are lots of applications of lenses: There are 2 types of lenses: Convex lenses Concave lenses Converging Diverging Keywords Image – a visual copy of an object Real – an image that can be formed on a screen Virtual – an image that cannot be formed on a screen Inverted – upside down Diminished – smaller Enlarged – made bigger, magnified Converge – rays meet and cross paths Diverge – rays separate from each and never cross paths. How can we make a lens more powerful? Make it more curved. Use a different material which refracts light more strongly. Convex lens F This image is real principal (can be axis Object F projected), inverted and diminished. 1. Draw a ray from the top of the object and straight through the optic centre. 2. Draw a ray from the top of the image, parallel to the principal axis until it hits the lens plane. 3. Continue the ray through the focal point F. 4. Construct the image. Convex lens Magnification = Image size ___________ This image is Actual size virtual, the right way up and magnified. F principal Virtual Object axis Image F 1. Draw a ray from the top of the object and straight through the optic centre. 2. Draw a ray from the top of the image, parallel to the principal axis until it hits the lens plane. 3. Continue the ray through the focal point F. 4. Construct the image. Convex lens - Summary This image is real, inverted and diminished. This image is virtual, the right way up and magnified. Image size Magnification = ___________ Actual size 1. Complete the ray diagram and describe the image formed. 1.Complete the ray diagram and describe the image formed. Real, inverted and diminished. 2.Complete the ray diagram. Draw the image and describe its nature. Calculate the magnification of the image. 2.Complete the ray diagram. Draw the image and describe its nature. The image is virtual, the right way up and enlarged. Calculate the magnification of the image. Magnification = image size/actual size = 22mm / 7mm = 3.1 Concave lens This image is always virtual, the right principal way up and Object Virtual axis diminished. Image 1. Draw a ray from the top of the object and straight through the optic centre. 2. Draw a ray from the top of the image, parallel to the principal axis until it hits the lens plane. 3. Construct the divergent ray that traces back to the focal point. 4. Construct the image. 3.Complete the ray diagram and describe the image formed. Object F Concave lens 3.Complete the ray diagram and describe the image formed. The image is virtual, the right way up and diminished. Object F Concave lens  4.Calculate the Convex magnification of the lens image. Object F F  4.Calculate the magnification Convex of the image. lens Magnifcation = 30mm/15mm =2 Object F F 5.The focal length of this lens is 10mm. Can a real image be formed? If so, how far would the screen need to be from the lens? Convex lens Object 5.The focal length of this lens is 10mm. Can a real image be formed? Yes If so, how far would the screen need to be from the lens? 13mm (+- 1mm) Convex lens Object F F 6.Complete the ray diagram and describe the image formed. Object F Concave lens 6.Complete the ray diagram and describe the image formed. Virtual, the right way up and diminished. Object F F Concave lens