This time Ali and Nelly achieved a really cool way to get brilliant colours. Anyone who has handled a CD will know that it can gleam in vivid colours when viewed at an angle. They argued that if a beam of parallel light, such as sun light is flashed on to a cd. It must throw out different colours. Their idea is depicted by this diagram.
Fig.1. Getting the colours from a CD.
In the 17th century there were no cd s. Sir Isaac Newton obtained the spectrum by passing the light through a prism. He distinguished seven colours.
Can this really work? Nelly’s friend Mehara actually carried out this experiment. First time she failed. There was too much light on the wall. When she tried on a white shady part of the wall about a meter away from Cd, she got the best results.
Now you may wonder what happened to Indigo which is the second colour in the former term VIBGYOR. These are the first letters taken in the reverse order. As an explanation for the omission of indigo let us quote the internet. “In modern usage,
Here the CD cannot be seen clearly. The white part on the carpet is the area lit by the sunlight. Only a part of the halo is seen here, but it is possible to get the complete circle. The order of colours can be remembered as ….
ROY Grows Blue Violets
( indigo is not usually distinguished as a separate colour in the visible spectrum; ”)
More activities There are many more variations a young scientist may try out.
Here is one suggestions\:-.
The path of light rays are not visible. It can be made visible by smoke. Try to get smoke between the CD and the wall.
Find more about Sir Isaac Newton.
Refer:- Dispersion of light under Nature of light.
6. Electrical conduction in materials.
You need 4 Paper clips, 9v battery. a torch bulb with a holder or an LED & some wires.
Diagram
Clean the ends of the wires by removing the insulation, Attach them as in the circuit diagram using paper clips or by some other way. If the detector is an LED, it will light up only for a current in one direction. Before attaching any object material the ends of the blue and the red wires must be connected to test the circuit. If the LED or the bulb lights it’s OK.
Then attach a strip of the material you wish to test to the circuit as shown.
Copy this chart into your note book and enter the results. Only a few examples are given here You can test any number of materials.
Item used | The guess of your friend | Your guess | Conductor / Semi conductor / Insulator. |
A strip of aluminium foil. | | | |
A strip of plastic. | | | |
A rubber band | | | |
A piece of cloth dipped in salt
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Test a few more materials available in your home.
Click:- Alan Mc Diarmid of NZ
2 b. Measuring Friendship.
Take the hand of your friend just as you shake hands. With your free hand hold the paper clip of the red wire. Ask your friend to grip the other clip. Make sure you make firm grips. If he is a good friend, the LED will light.
7. Measuring Rainfall
It was raining cats and dogs. Ali and Nelly saw rain water getting collected into a large barrel. Unlike the water that falls on the ground, which either gets soaked up or flows down the slope into streams, water in a barrel will stay. So they got an idea. Fig.1 All the rain above the barrel gets inside. Their dialogue was as follows; Ali :- There ! We can measure the water in the barrel”. Nelly:- “I cannot remember the formula to find the volume of water in a cylinder” Ali:- “ No need. We can measure the height.” Nelly:- “The height of rain? “ Ali:- “No. silly girl. After the rain we can dip a stick into the barrel and find out the height of water collected in it”. Nelly:- “ How brainy you are? Now I remember , rain fall is always given in millimeters.”
You don’t need a barrel for this. We can do it in a very small scale. Here are the steps for you to measure the rainfall every day; so that you may know the usual dry months and wet months of the year.
Step 1
Get an empty plastic mega bottle. Draw a ring round the neck with a marker. Get a friend to hold the bottle tightly if you cannot clamp it. Take a bread knife and carefully cut an insertion. [Beware- Knife might slip on plastic.] Then with a pair of scissors you can easily separate the top part of the bottle. This is shown in Fig.2.
 Fig. 2 Making an insertion with a bread knife.
Step 2
The bottom of these bottles is usually curved. How can that be made flat? One way is to pour something like cement. Mix one part of cement with about two parts of soil make it into a paste with water and add it until the curved bottom becomes flat. If cement is not available you may even use some other substance like clay. If you use a substance like sand you must add water to cover up the pores.
Step 3 Unscrew the cap and make a few holes in it with a nail. Then tighten the cap to the top part, invert it and slide it into the bottle as a funnel. Then paste a strip of graph paper to measure the height of water.
Fig.3 Bottle Rain gauge.
Keeping Records. It is interesting to keep a record of rain fall. This can be done very neatly using a square ruled exercise book or better a graph book. If the rain fall was 10mm , you can colour up to the violet line. On the second day it was 20.5 mm. Third day no rain. 4th day 2mm.only. This is how you should keep your records
8 . Making a sprayer.
If you blow air , will there be a high pressure or a low pressure in the stream?
"It ought to be Uigh"
Experiment
Take two long strips of paper . Let them hang from your hands as shown here. Then blow air between the two strips. What do you think would happen
If you use a blower the effect would be more impressive.
Big. Blow air between the two strips.
It was Daniel Bernouli, a brilliant mathematician who solved this in the 18th Century. So the pressure phenomenon that result from fluid flow is described as Bernouli Effect. (It is worthwhile reading his life history in the Biography category.) |
Bernouli Principle
Fig. An application of the Bernouli Principle.  Keep a thin plastic tube dipped in a cup of water. The water may be coloured so that you could see the level clearly. Take a barrel from a ball point pen and cut it into two. Fix the part with the pointed end to a balloon. Tie it up with a string so that air may not leak. Keep the other part verticlly with one end dipped in water. Now blow the balloon through the jet tube .. Place the jet in line with the opening of the tube and release the air . Water will get drawn up. Do you know why? If you wish to know about Bernauli brothrs and their father go to Bernauli Family. |
9. Magic string Here is an interesting experiment that can make you a magician.. There is a ring or some light object hanging from a loop of a cotton thread. You can utter a manthra and burn one strand, the ring will not fall. If you burn the other strand, without the manthra, the ring falls down','Method. Ask for a cotton thread about a meter long from your mother. Make a strong salt solution into a saucer and immerse about half of the thread in the solution. That part of the thread will absorb the salt. Keep it for about ten minutes and then dry the thread by keeping it in the sun.. After drying there will be no visible difference between the two ends. Then borrow a gold ring and pass the thread through that and tie the two ends making a reef knot. Place a metal ruler or a rod on a table and keep it steady by a weight such as a book. Insert the top end of the loop into the rod and let the ring hang as shown in the picture. It is important to keep the salted strand and the other part separate. It is easy to identify the salted end if you let the knot come to that side.
Ask your friends what would happen if you burn the string. Many will say, “ The thread will break and the ring will come down”. Get a candle flame and burn the salted strand uttering some sort of manthra just to deceive your friends.. To everybody’s great surprise the thread will not break. Then ask the same question again with regard to the other thread.. Then burn the other end without the manthra. The ring will fall.
Why it happened? Cotton which is a compound when burnt a black substance Carbon is formed. ( This is the same as charcoal) These particles are not linked together tightly. In the case of salted threads salt which remains without burning can bind the carbon particles together.
Projects for the young research scientists.
1. Use cotton threads of different thickness and find out what weight they can hold. 2. Use different solutions and find out how many paper clips are necessary to break the thread. Examples of solutions:- sugar, soap , lime etc.
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