1) Have you been to the haunted house in Disneyland ? You follow a track and look down, through a huge glass (it's a half-silvered mirror, you can see your reflection but also transmitted light). You see ghosts going through tables and moving around. Can you explain the trick ? You know that light can be reflected by glass. Explain the trick.
(we should take a trip there , right ? It will beautifully illustrate the law of reflection)


2) A mirror can bounce back the light or any other EM wave like a radio wave. But if you use a retroreflector made out or 3 mirrors you can get them bounce in the same direction. In 2 D, you need only 2 mirrors to make a retroreflector. The 2 mirrors have to make a 90-degree right angle.

Complete the path of the light.
Why stop sign are made of retroreflectors ?
Why scientists placed retroreflectors on the moon ?



3) Any surface making right angle can be a retroreflector. A plane with such features can easily be seen by radar. Why ?
For example, a wing can make a right angle with the body of the plane. The army has developed special planes without any corner reflector. This is called the stealth technology used during Irak war. The planes fly unseen or ship can sail unseen. Find 2 pictures to illustrate this technology. (a plane and  a ship.) Staple with your HW)

4) To observe an object, you need light to bounce off this object. There is a principle you should know. Let's say you are using a microscope. Visible light is used to "see" the object. (It will bounce back of it). There is something to remember. To be able to see an object, the wavelength of the light (here visible light) has to be larger than the length of the object. If this is not the case, the object can't be seen. (because of a phenomena called spreading of light or diffraction, see next chapters)
Find the wavelength of, let's say, green . L = ___________m. (do some search)
A hair is 25 micron (1 micron = E -6m). Can you see it? why ? .
An atom is about E-10m. Can you see it ? You can see an atom using what kind of microscope
 (extra credits if you find) ? In that case, you are using waves made of ____________.

5) (use an encyclopedia like wikipedia) Who came first with the idea: light is made of particles? _________/ He called them corpuscles. Who disagreed with this giant and said light is a wave? ___________
  However, the corpuscles view prevailed until ________ showed that light behaves like a wave (using 2 sources of light, he showed that the light coming from the 2 different sources can reinforce each other or cancel each other. Like water waves producing constructive or destructive patterns. THis is called interference)
This new view replaced the old one in the 19th century.  Then James Maxwell confirmed this idea, showing that light is an __________. James Maxwell developed 4 equations that unified _______ and _________. Before electric and magnetic phenomena thought to be unrelated to teach other. His equations describe the behavior of ____ waves.
Then every one got confused again because ____________, in  1905, brought back the idea of light as ________. THese __________ were not called corpuscles any more more but ___________ or quanta of energy. They are really particle-waves. not a particle , not a wave but something in the middle. Each of these particle-wave carries an energy E proportional to their _______. This is called the Planck formula. ___________ got the nobel prize in 1923 because of his discovery. Later, De Broglie showed that even electrons can behave as ___________. That's why you can use them in an electronic microscope. You can also use neutrons.

6) Explain briefly the photoelectric effect. It can only be explained if you consider light made out of photons (particle-wave) or quanta of energy.


7) The speed of light is 300,000 km/s. How it takes for the light to cover 1 foot (30cm) ?
How long it takes for the light to travel from the Sun to us ? in minutes. So if the Sun vanishes all of a sudden, how long it will take to realize that ? What will happen to Earth ? (think also speed)

© haplosciences 2000-2007 -
vente par correspondance jeux éducatifs,  jeux scientifiques clement o ni , jeux educatifs
Amina, Wanikou, mael r oi du mail , laboratoire chimie, fiches e xperiences,  thomas au temps des chevaliers, Pilou  la classe,
 fichiers animation les francas, jeux engrenages singes, engre nages juniors, engr e nages train safari, prismes
microscopes, p rismes, jeux gyzmo sous la mer, jeux engrenages, c o loriage, travaux manuels, animaux, sciences, vente prismes
tub es a essai, apprendre l a nglais , coloriae , anglais maternelle, jeux clémentoni, cahiers maternelle, anglais enfants, anglais petits