The Plan… 6 May 2013

• Review Homework from last day: CYU P. 215 #1-9 Activity 6.2 (hand this in)

• Start Section 6.2 Extending Human Vision

PPT & Worksheet

• Activity 6.5 – Experimenting with a Simple Lens Do this on your own and hand in…

• Hand in any unfinished work: Human Eye Function Worksheet etc.

• OSS “Citizenship” Nomination Information

(c) McGraw Hill Ryerson 2007

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6.2 Extending Human Vision

• Human knowledge about our planet and the universe was very limited until we developed tools to extend our vision.

• The tools we use for these inquiries may seem quite different from each other, but they are based on the same understanding of light, mirrors, and lenses.

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Focus! Focus! Focus!

• In order for the light rays passing through a lens to form a clear image, the screen that is receiving the image must be the correct distance from the lens. The screen must be at the place where all the light rays from a given point on the object converge.

• If the screen is placed too close to the lens, then the light rays do not fully converge by the time they strike the screen. There will be an image formed, but it will appear blurred.

• If the screen is too far away, then the light rays converge and then begin to diverge before they strike the screen, resulting in a blurred image.

• Adjusting the distance between the screen and the lens to make a clear image is called focussing. Focussing is an important step in using optical devices such as microscopes, telescopes, binoculars, and cameras.

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6.2 Extending Human Vision

Microscopes• A compound light microscope uses

two convex lenses to magnify small, close objects. Magnify means to make the image look

larger than the real size.

• To focus the image, the object is moved closer to or farther away from the object lens. Adjusting the distance to make the image

clear is called focussing.

See pages 216 - 217 4

ConvexLens

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Refracting Telescopes

• A refracting telescope has a convex lens to collect and focus light from a distant object, and a convex eyepiece lens to magnify the image.

• Problems with refracting telescopes include: Large objective lenses flex, due to

their own weight and distort the image.

Glass lenses, even of the highest quality, absorbs some of the light and are expensive.

See page 2195

Convex Lens

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• A reflecting telescope uses a concave mirror, a plane mirror, and a convex lens. Light enters the telescope and is focused

after reflecting off the concave mirror. Before converging at a focal point, a plane

mirror reflects the light towards the eyepiece. An image is formed here.

The convex lens in the eyepiece magnifies the image.

• Most large telescopes are reflecting telescopes.

Reflecting Telescopes

See page 2206

Hubble Space Telescope

• The Earth’s atmosphere blurs the view of objects in space. • To overcome the blurriness of our view into space, the Hubble Space Telescope

was launched in 1990. The Hubble Space Telescope is a type of reflecting telescope that uses two mirrors to collect and focus light to form an image.

• Hubble Space Telescope has produced images much sharper and more detailed than the largest ground-based telescopes.

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• Binoculars are actually two refracting telescopes mounted side by side.

• To shorten the length of the tubes in binoculars, prisms are used to reflect the light back and forth.

Binoculars

See page 2218

Convex Lens

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Cameras

• Light enters the camera through an opening called the aperture.

• Light then passes through a lens which focuses the image on the light detector.

• Cameras can have different types of lenses. Wide-angle lens allow for a wide field of view.

Have short focal lengths that produce a relatively small image of the object but have a wide field of view.

Telephoto lenses allow distant object to appear larger. Telephoto lenses have longer focal lengths. The

image through a telephoto lens seems enlarged and closer than it actually is.

See page 222

A telephoto lens

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Cameras Have Similarities to Human Eyes

See page 223

EyeEyelid

Iris

Retina

Rods and cones

CameraLens capDiaphragmCharge-coupled device(CCD)pixels

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Lasers and Laser Surgery

• Laser light is light of only one wavelength. Compared to Sunlight and light from an

incandescent light bulb which contain a mixture of waves of different wavelengths

• Can travel great distances without spreading out and contains a lot of energy.

• Lasers can be used in place of scalpels in surgery. Remove cataracts Reattach retina Laser eye surgery to reshape the

cornea. See page 224

Laser surgery

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Optical Fibres

• Optical fibres are transparent glass fibres that can transmit light from one place to another.

• Optical fibres transmit light using total internal reflection. Total internal reflection is when light

strikes a boundary between two materials and is totally reflected.

• Optical fibres are used for: Medical procedures (orthoscopic

surgery) Telecommunications (telephone, internet,

video)

See page 225

Optical fibre

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Now it’s your turn…

• Activity 6.5 Do it on your own, answer all

questions, hand in…

• Reading Checks P 223 & 226 I will check tomorrow…

• Finish Worksheet 6.2 We will discuss on Tuesday…

• Tie up any unfinished work…

• @ 2:35 OSS Citizenship Info

• P 216

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