Light...

1. Light... • ORB Education Quality Teaching Resources • ORB Education • Visit http://www.orbedu.com for the full, editable versions with solutions. • ScP033 – Mixed PowerPoints

2. Belinda Consider the picture below….. Why can the Belinda see the cat, but not the dog?

3. Let’s start at the beginning…. Light travels in straight lines This is why we cannot see around corners. X This is also the reason why shadows occur when something gets in the way of the light.

4. How do we see things? For you to be able to see an object, light must travel from the object to your eye. The light that hits the object usually comes from somewhere else … … maybe the Sun … … or perhaps from a light bulb, candle or torch. These are called ‘light sources’.

5. How do we see things? So, in order to see an object, light must travel from the source to the object It must then be reflected off the object and travel to your eyes.

6. So, looking at that picture again... Belinda can see the cat. This is because light from the source can reach the cat ... … and the reflected light from the cat can travel in a straight line to Belinda’s eyes.

7. So, looking at that picture again... Belinda can’t see the dog. Even though light from the source can reach the dog ... … the reflected light from the dog cannot travel straight to Belinda’s eyes.

8. Consider the picture below….. Can the girl see the person in the mask? On your worksheet, draw light rays in order to determine whether she can or not. And the answer … No

9. Summary so far • Light travels in lines that are … • … straight. • Some things, such as the Sun and light bulbs give out their own light. These are called … • … light sources. • Other examples of light sources are … • … candles and torches.

10. Summary so far • Most things don’t give out their own light. They simply … • … reflect the light that has come from a source. • For you to see the object, this reflected light must be able to … • … travel in a straight line to your eyes.

11. Reflection from Smooth Surfaces A very smooth surface, such as a mirror or a still pond, will reflect a beam of light in one direction only. Mirror A clear reflection is seen in the surface. This type of object is said to have a glossy (or shiny) surface. These thin beams of light are called ‘light rays’.

12. Surface of Paper (under a microscope) Reflection from Rough Surfaces Most objects are not smooth, especially when viewed under a microscope. In these cases, the light is reflected in all directions. A clear reflection is not seen in the object. This type of object is said to have a ‘Matt’ surface.

13. Which brings us to the Law of Reflection Mirror If a ray of light is directed at a mirror … 700 … at a certain angle … … it will be reflected from the mirror … 700 … at exactly the same angle.

14. Mirror 700 700 Which brings us to the Law of Reflection Or, in more theoretical terms: angle of incidence, i 200 Normal 200 angle of reflection, r angle of incidence =angle of reflection angle i =angle r

15. mirror Drawing Rays Show on your diagram what happens to the ray of light next. 400 400 Press the Spacebar when you have finished.

16. mirror Drawing Rays … and this ray of light? 300 300 Press the Spacebar when you have finished.

17. The Pyramids The law of reflection has been known for some time. In fact, the pyramids in Egypt were decorated by people who understood it. The artists working in the Pharaoh’s tomb needed to have enough light to see their painting. They didn’t use oil lamps or candles, because that would have left marks on the walls from the dark smoke.

18. The Pyramids So that light could be reflected into each chamber, polished metal mirrors were placed along the corridors! The light could then reflect all the way to the artist in the tomb.

19. The Pyramids Unfortunately, each time light is reflected, some of it is absorbed. The light intensity would drop with each reflection. The amount of light reaching the burial chamber would have been very small. The artists eyes, however, would have slowly adjusted to the small amount of light. When the artist left the tomb, the daylight would have seemed blindingly bright.

20. The Pyramids In this way, the artist’s life was dedicated to the Pharaoh.

21. mirror 100 100 ray box Light Experiments Claire is performing a light experiment. Using a ray box, she sends a ray of light towards a mirror. She places a piece of paper underneath the ray box and mirror, so that she can mark in the direction of the ray before it strikes the mirror. She can also trace the reflected ray.

22. Light Experiments Claire carries out the experiment five times, using different angles each time. These are the angles she directed the ray from: a. 100 b. 200 c. 300 d. 450 e. 600 Using this information, fill in the table on your worksheet.

23. Angle that light strikes the mirror Angle that light reflects from the mirror 100 100 200 200 300 300 450 550 600 600 Light Experiments This is the table that Claire completed after measuring each of the angles. Which angle must Claire have recorded incorrectly? Answer: 450 / 550

24. Remainder removed from this sample presentation. • ORB Education Quality Teaching Resources • ORB Education • Visit http://www.orbedu.com for the full, editable versions with solutions. • ScP033 – Mixed PowerPoints