January 1, 0001

Science Workshop 101

Session title: Understanding light Session description: This session introduces some fundamental concepts of light. At the end of this workshop, students will know:

Light travels in a straight line.
It has a constant speed everywhere in the Universe.
Light can change direction by reflection and refraction.
How to draw ray diagrams with convex and concave lens
Understand dispersion, which is the splitting of white light into seven colors.
Take a peek into the micro-cosmos - the “invisible” microscopic world all around us.

Total duration: 4 hours. Kit materials:

12-page Workbook (will be provided)
Pencil
Scale
Laser (red)
500 ml bottle of water
Ray box
Mirror with stand
Glass slab
Concave lens
Convex lens
Prism
Foldscope
Prepared slides (50 nos) (will be provided)
Color pencils.

To buy the kit components:

[Topsun Light and Optic class demo kit](http://Topsun Light & Optic kit Class Demo kit) contains a ray box, all the lenses and more, needed for most of the experiments. It comes in a bag for safe storage. Cost: Rs. 2859. (If the cost is excessive, individual components can be bought and stored)
0.5w mini red laser pointer. Cost: Rs. 85.
[Optical glass prism](http://Optical Glass Prism). Cost: Rs. 168.
Foldscope with one prepared slide. Rs. 499.
Foldscope Deluxe Individual Kit (optional, only if you want to attach to phone). Rs. 2000.

Approximate Total cost: Rs. 3000.

Concept	Activity	Content	Time
		Where does light come from?
		Mainly…the Sun!
	Question Poll	How does the (sun)light reach Earth?
Rectilinear motion of light	Workbook page 1: Using a pencil and scale, join the two points to create a straight line.
	Using the red laser pointer in the kit. Place it along the line and see that light does indeed travel in a straight line.		10 mins
		It takes 8 mins for light to travel to Earth. Distance from Sun to Earth: 150 million kilometres.
	Workbook page 2: Using the formula speed = distance / time, calculate the speed of light. Use a calculator, if you need to.		15 mins
		This is the fastest man on earth. He ran 100 metres in 9.58 seconds. Now compare his speed with the speed of light.
Speed of light.		The speed of light is the same everywhere in the Universe. It is a “constant.”
	End of Session I: 30 mins		Break: 10 mins.
	Question poll.	We know that light travels in a straight line. But, can we change its direction?	5 mins
	Workbook page 3: Get the room as dark as possible. Shine the red laser on the bottle of water. Repeat the same thing with a rectangular block of glass. You can also try this using the ray box. Trace the ray diagram on the given page.
Reflection	You will observe that a part of the light will reflect back. This may not be visible unless the room is sufficiently dark.
Refraction	but most of it will “bend” and pass through the water.		15 mins
		Let’s understand reflection. Reflection is just like a bouncing ball.
	Workbook page 4: Setup the ray box and a mirror as shown below (mirror acts like the smooth surface of water). Now, aim the “incident” ray on the mirror, and observe where the “reflected” ray goes. Calculate the angle (using a protractor) of incidence, and reflection measured from the normal, which is a line perpendicular to the mirror. Repeat three times. Fill the table on the given page.		25 mins
	Question poll	What is the relationship between the angle of incidence and angle of reflection?	5 mins
		Ans: They are the same.
		Let’s understand refraction now.
	Workbook page 5: Setup the ray box and a glass slab as shown below. Draw the ray diagram. Repeat with three different angles.		10 mins
	Question poll	Does light refract at every angle of incidence?
Total internal reflection		Ans: No. At a certain angle, the light beam does not enter the glass slab at all.
	End of Session II: 60 mins		Break: 10 mins
		Getting deeper into refraction. How does light bend when it passes through “curved” glasses?
Divergence.	Workbook page 6: Place a concave lens in front of the ray box. Draw the ray lines before and after the light rays pass through the lens.		20 mins
Convergence..	Workbook page 7: Repeat for convex lens.
		Why do stars twinkle?
Refraction	Workbook page 8: Draw a star. Then draw the layers of the atmosphere, of different densities. Draw a light ray from the star - it will bend (zig-zag) through the layers before it reaches your eye.		10 mins
		Ans: Refraction. Tonight, walk outside and observe the stars twinkle.
	End of Session III: 30 mins		Break 10 mins
	Question poll	Where does color come from?	5 mins
	Workbook page 9: Place the ray box, prism and paper, as shown on the page. Turn on the red light. Observe. Turn on the white light. Observe.		20 mins
	Question poll	What happened when the white light went through the prism? And why?	5 mins
		Ans: White light contains all the colors our eyes can see.
	Workbook page 10: Fill out the prism rainbow on the page.
Dispersion		Which color bends the most? The least? Which property of light causes the rainbow?
		Ans: Violet. Red.
	End of Session IV: 30 mins
	Question Poll	How does a microscope work?	5 mins
	Workbook page 11: Trace the ray diagram on the given page.
		Ans: A microscope uses a convex lens to bend the light towards our eyes. This “bending” of light creates an image in out eye that is larger than the actual object.
	Take out the foldscope. Insert one of the given slides.
	Workbook page 12: Draw what you see. Use color pencils. Label it. For example: This is Xylem tissue, which is that part of the plant that helps carry water up and all around. What you are seeing are water-conducting cells.		45 mins
	End of Session V: 60 mins

After this session, students can participate in the next workshop - “How we see the world.” (The workshop is still WIP).

External References

https://foldscope.com/pages/user-guide#trouble

https://rsscience.com/microscope/