Lesson 21 - Optical Devices The earliest optical devices Everyday optical devices Telescopes… Refractive and Reflective Microscopes/Glasses/Binoculars

Review of Optical Devices An Optical device is any technology that uses light Optical devices can be as simple as a mirror or as complex as the Hubble telescope The invention of optical devices has lead to many great discoveries that have shapes our daily lives

Purposes of Optical Devices The purpose of any optical device is to collect and gather light Whether its for telescopes, cameras, microscopes, or simply our eyes… they are designed to gather light

Views from Hubble

Purposes of Optical Devices Without Hubble’s ability to collect light from a huge area and focus into an image, we would never have enough light to see those amazing pictures The greater the light gathering ability, the more detail we can see from further away objects

Comparing Gathering

How Much Better Is It? Below we see two light gathering devices, each with a different diameter… How many times more, or how much more light can the larger opening gather? d = 10 cm d = 5 cm

Calculating Surface Area Surface area of a Circle: SA = 3.14 x r² Example SA = 3.14 x r² SA = 3.14 x r² SA = 3.14 x 2.5² SA = 3.14 x 5² SA = 3.14 x 6.25 SA = 3.14 x 25 SA = 19.625 cm² SA = 78.5 cm² 78.5 ÷ 19.625 = 4 Therefore the larger telescope with twice the diameter actually has 4 times the light gathering ability d = 5 cm d = 10 cm

Telescopes There are two types of telescopes: REFLECTIVE REFRACTIVE Refractive telescopes use lenses to bend the light to a focal point for our eyes Reflective telescopes use a concave mirror to reflect the light to a focal point for our eyes Which is better… WHY?

Telescopes There are two types of telescopes: REFLECTIVE REFRACTIVE

PROS & CONS Refracting telescopes are cheaper to make… but there are draw backs Both telescopes can be made to gather equal amounts of light… However, refractive telescopes suffer from CHROMATIC ABERRATION so after a certain point they blur the image to much Reflective telescopes don’t have this problem so they can be made as large as possible and the image will still be intact

Chromatic Aberration Chromatic Aberration is the tendency for different coloured light to bend at different amounts during refraction Therefore, when you pass you coloured light through a lens, all the light is not bent to the same spot and the image is blurred

Chromatic Aberration

Microscopes Microscopes are also designed to gather light, but they do so from a very small area up close Microscopes collect what little light there is at the microscopic level and then expand the image using refraction for us to see We can only see tiny objects to a certain point before their just isn’t enough light for our eyes to detect an image

Microscopes Most microscopes use a light source at the base to shine onto the specimen from below because without it there would not be enough light for our eye to see You will need to do more research on microscopes in the next unit

Other Optical Devices Magnify glasses help enlarge light by gathering light from a small area and enlarging it Eye glasses refract gathered light to focus it on to our retina when our own lens cannot Convex mirrors allow us to see a large surface area on a small space Concave mirrors allow us to reflect light to a focal point

Homework Tonight You are being given a worksheet that covers the material we just went over Use the sheets as study tools and for practice questions that could be on the Unit End Exam We will be going over this worksheet tomorrow!!

Textbook Pages You may look at the following textbook pages to help you with your assignment… they compliment what we have talked about today Use pages 221 - 226 in the Science Focus 8 Textbook to help you complete the worksheet. Use pages 182 - 184 in the Science in Action 8 Textbook to help you complete the worksheet.