Revision Revision of ray diagrams Quiz How does the eye work video:

Describing images Match these words to the descriptions: diminished; inverted; magnified; real; upright; virtual _________ = bigger than the object _________ = smaller than the object _________= upside down (not the same way up as the object) _________= the same way up as the object _________ = you can project the object on to a screen _________ = you cannot project the object on to a screen

Describing images Match these words to the descriptions: Diminshed; inverted; magnified; real; upright; virtual _________ = bigger than the object _________ = smaller than the object _________= upside down (not the same way up as the object) _________= the same way up as the object _________ = you can project the object on to a screen _________ = you cannot project the object on to a screen magnified diminshed inverted erect real virtual

FF2F focal length 2 x focal length OBJECT (simplified) RAY DIAGRAMS:RULES Image – diagram gives position and size How can you describe the image here? Inverted, diminished and real. (You know it‘s real because the rays „really“ pass through it.)

1. Draw the following on graph paper 2. Draw an object outside 2F at the position shown and at the size shown FF2F 2cm large square 3. Apply the ray diagram rules and draw in the image 4. Classify the image by filling in the table below. Repeat for other positions Object pos.Image pos.mag/dimupright/Invertedreal/virtual outside 2F at 2F between F & 2F at F inside F Uses

FF2F 1. OBJECT OUTSIDE 2F IMAGE: REAL, INVERTED, DIMINSHED IMAGE POSITION: between F and 2F uses next diagram Arrow key to animate slide

FF2F 2. OBJECT AT 2F IMAGE: REAL, INVERTED, SAME SIZE IMAGE POSITION: at 2F uses next diagram Arrow key to animate slide

FF2F 3. OBJECT BETWEEN F AND 2F IMAGE: REAL, INVERTED, MAGNIFIED IMAGE POSITION: outside 2F uses next diagram Arrow key to animate slide

FF2F 4. OBJECT AT F IMAGE: NO IMAGE FORMED (rays don’t meet) IMAGE POSITION: none (or at infinity) uses next diagram Arrow key to animate slide

FF2F 5. OBJECT INSIDE F IMAGE: VIRTUAL*, UPRIGHT, MAGNIFIED IMAGE POSITION: inside 2F & SAME SIDE AS OBJECT uses Concave lenses *VIRTUAL Image: Light does NOT actually pass through it – cannot be projected onto a screen Arrow key to animate slide

FF2F 6. CONCAVE (DIVERGING) LENS IMAGE: VIRTUAL, UPRIGHT, DIMINSHED IMAGE POSITION: INSIDE F SAME SIDE AS OBJECT uses quiz Arrow key to animate slide Same type of image for all object positions STOP

1. OBJECT OUTSIDE 2F IMAGE: REAL, INVERTED, DIMINSHED IMAGE POSITION: between F and 2F Cameras, eyes Back to diagram

2. OBJECT AT 2F IMAGE: REAL, INVERTED, SAME SIZE IMAGE POSITION: at 2F Back to diagram Copying camera

3. OBJECT BETWEEN F AND 2F IMAGE: REAL, INVERTED, MAGNIFIED IMAGE POSITION: outside 2F Projectors Back to diagram

4. OBJECT AT F IMAGE: NO IMAGE FORMED (rays don’t meet) IMAGE POSITION: none (or at infinity) Searchlights Back to diagram

5. OBJECT INSIDE F IMAGE: VIRTUAL, UPRIGHT, MAGNIFIED IMAGE POSITION: inside 2F & SAME SIDE AS OBJECT Back to diagram Magnifying glass

6. CONCAVE (DIVERGING) LENS Used in spectacles: Short sight ‘Myopia’Long sight ‘Hyperopia’ Eye lens too strong: spectacle lens diverges light to bring back into focus Eye lens too weak: spectacle lens converges light to bring back into focus

How does the eye work?.

Quiz Camera versus the eye watch?v=psp_8xJfeWU watch?v=OGqAM2Mykng

Write the colours of the rainbow? - Red - orange – yellow – green – blue – indigo - violet Which colour has the shortest wavelength? - blue What is white light? - The colours of the spectrum (or red, blue and green) shining together. All the cones are activated the same amount and we see white. What is black? -No reflected light at all. Why do things usually look grey in the evening? -Our cones don‘t work well in low light levels. -Our rods do work but don‘t detect colour.

What colour do we see if we shine blue and green light at a white wall? - cyan and why do we see cyan? - Our blue and green cones detect the blue and green light and our brains tells us that it is cyan. What colour do we see if: we shine blue and red light at a white wall? - magenta we shine blue and red light at a green wall? - black And why? -The red and blue light is absorbed by the green wall. Green things only reflect green light and there is no green light.

Which colours do televisions and computer screens usually use? - red, green and blue and why do they use these colours? - They can make every other colour with them. How can they make yellow? - Red plus green How do they make orange? - Red plus green but more red than green

What colour do we see if you put a green filter in front of white light? - green and why? - Green filters only let green light through and absorbs the other colours. What colour do we see if you put a green filter in front of red light? - black and why? - Green filters only let green light through and absorbs the red. What colour do we see if you put a green filter in front of cyan light? - green and why? - Green filters only let green light through and absorbs the blue.

Which colour inks do printers usually use? - Cyan, yellow and magenta and why? - You can make every other colour with these colours. How do printers make red? - They add magenta and yellow How does that work? -Magenta reflects red and blue light but absorbs all green light. -Yellow absorbs the blue light. This means that there‘s only red light left to be reflected.

Why does green grass look green? - It relects green light and absorbs most of the other colours. What colour does green grass look in blue light? - black And why? -There‘s no green colour to be reflected and all the blue gets absorbed.

Draw a ray diagram with a convex lens when the object is between F and 2F. Describe the image. - invertzed, magnified, real Name one use? -As a projector.

Describe the image when you look at an object in a magnifying glass. Magnified, upright and virtual. Draw the ray diagram.

Label the parts of the eye. A – pupilB – lensC – ciliary muscle D – optic nerveE – retinaF - iris A B C D E F

Which part of the camera focusses the light? - The lens. Which part of the eye detects the image? -The retina Which part of the camera detects the image? -The film What does the focussing ring in the camera do? -It moves the image backwards and forwards so it is exactly on the film – that means you get a clear image on the film. How does the eye make sure that you get a clear image on your retina? -The ciliary muscle changes the shape of the lens. If the object is nearer the ciliary muscle makes the lens more rounded (the focal length of the lens is then shorter) and the image is on the retina. For an object which is farther away the lens become flatter (less rounded) again.

What does the diaphragm do in the camera? - It lets more of less light in. How does the eye change the amount of light hitting the retina? -The iris changes its shape and makes the pupil bigger or smaller. A bigger pupil lets more light in. If you are suffering from myopia, what problem do you have? Describe it -You can‘t see objects which are far away. Your eye focusses the image in front of the retina. Which lens can you use to correct it? -A concave lens. Draw a picture to show how that works.

Some people can‘t see objects near to their eyes. Why might this happen? (2 things) -The eye ball can be quite short from the lens to the retina – so the image forms behind the retina. -The lens gets harder when you get older and cannot become rounded enough – the image is formed behind the retina. Which lens can you use to correct it? -A convex lens. Draw a picture to show how that works.