# Is Light a wave or a particle

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```							Physics Internet Lab on LIGHT                  Name ______________________________

Is Light a wave or a particle?
1) Skim the following websites and give historical and current evidence that light
behaves like a particle and that it also behaves like a wave.

http://www.antonine-
education.co.uk/Physics_AS/Module_1/Topic_3/topic_3_particle_model_of_light.htm

http://www.liverpoolcollege.org.uk/Science%20Magazine/light.htm

http://www.olympusmicro.com/primer/lightandcolor/particleorwave.html

2) Using above website, define the following:
a) reflection

b) refraction

c) diffraction

Reflection in Curved Mirrors
Play with the applet below and answer the following questions:
http://www.phys.ufl.edu/~phy3054/light/mirror/applets/Welcome.html
a)concave mirrors
1) If the object is as close to the mirror as possible, where is the image?_______ Is it real
or virtual?______

2) As the object is moved away from the mirror towards the focal point, what happens to
the image?
3) Where did the image go when the object was at the focal point?

4) What happens to the image as the object moves outside the focal point?

At what point are the object and the image at the same place? ___________
b) convex mirrors
5) Play with the convex mirror applet. Is the image ever real? ___________
6) Is the image upside down? _______
7) Is the image ever smaller? _______

Color
Play with the color applet below and answer the following questions:
http://pdukes.phys.utb.edu/PhysApplets/Colors/TabbedcolorBox.html

1) What colors result when you mix the following colors of LIGHT?
a) red and green _____________      red and blue ____________
green and blue ________          red and green and blue ____________________

2) What colors result when you mix the following colors of pigment?
a) yellow and cyan _____________ yellow and magenta ____________
cyan and magenta ________        yellow and cyan and magenta _______________

Polarization
Go to the following website on polarization.
http://micro.magnet.fsu.edu/primer/java/polarizedlight/filters/index.html

1) What is polarization?

2) With the first angle on 0º, for what angles of the second polarizer does the light wave
completely disappear?

Refraction
Go to the website below, play around with it and answer the following questions:
http://stwww.weizmann.ac.il/lasers/laserweb/Java/Twoangles2.htm
1) If the index of refraction of each medium is 1.0 (air), with a 45º incident angle, what is
the angle of refraction? _______ (Remember the angle of refraction is always compared
to the line normal to the interface of the two media.)

2) Change the index of refraction of medium 2 to 1.333 (water’s index of refraction).
With the same 45º incident angle, what is the angle of refraction? ________
Did the refracted light ray bend towards the normal or away from the normal?
_________
3) Now reverse the indices of refraction: Make the index of refraction of medium one
1.333 (water) and the index of refraction of medium two 1.00 (air). With an incident
angle of 45º, what is the angle of refraction? __________
Does the refracted light ray bend towards the normal or away from the normal?
_________

4) With an incident angle of 47º, what is the angle of refraction? __________
5) At what incident angle does the refracted ray get reflected and not refracted? ______
This is called “total internal reflection” at the “critical angle”.

6) Using an index of refraction of 2.419 (diamond) for medium 1, and an index of
refraction of medium two 1.00 (air), what is the critical angle? ___________

7) Summarize under what conditions the refracted ray bends away from the normal and
when it bends towards the normal.

8) Why does light get refracted in the first place?

9) What is an index of refraction?

10) Go to the website below and find out how a rear view dimmer setting works. Explain
below.
http://sol.sci.uop.edu/~jfalward/refraction/refraction.html
Explanation:

Diffraction
Go to the website below, play around with it on the following settings:
1) The top control is called “setup”. Choose “obstacle” to see how water and light bends
around an obstacle.

2) Choose “half plane” which simulates water waves or light waves bending around
something jutting into their path.

3) Choose “double slit” to see interference patterns (areas of constructive interference and
destructive interference).
4) Play around and see what you find out. What else did you find interesting?

Skim through the following website and answer the following questions
http://sol.sci.uop.edu/~jfalward/physics17/chapter12/chapter12.html
1) Give an example that compares and contrasts specular and diffuse reflection.

2) What percent of light is reflected off a windowpane?

3) On the page with the cartoons of the black man with a hat, what if anything is wrong
with the statements about convex and concave mirrors?

4) When light travels from one medium to another one of higher density, does the light
ray bend away from or towards the normal?

5) Does refraction make a swimming pool seem deeper or shallower than it actually is?

6) Does the sun actually set when we see it set? Explain.

7) How does a water mirage work?

8) When white light is dispersed by a prism, which wavelength of light is bent more?

9) Explain how we see a rainbow.

10) What is a “critical angle?”

11) What is the critical angle for diamond in air?

12) Why do stars twinkle?

13) Light normally travels in straight lines, but it “bends” in an optical fiber. Explain.

14) Which are more successful in dislodging electrons from a metal surface, photons of
violet light or photons of red light? Why?
Go to the following website and answer the questions below:
http://rabi.phys.virginia.edu/HTW/sunlight.html
1) Why is the sky blue?

2) Why are sunsets red?

Skim some of the other questions, and write one question/answer to the topic that
interested you most.
3)

```
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