2012年2月9日星期四

Project Details


Organisation: Singapore Science Centre, CRADLE Department
Mentor: Dr Wulf Hofbauer
Group Members: Lim Jia Qi Jamie, Teo Ting Yu, Wan Meng Yang
Name of project: Mapping 3 dimensional standing waves in a microwave oven (self initiated)

Introduction


Microwave ovens are common in our daily life, but we fail to explore how standing waves inside have been formed and how the waves were used to heat up our food.

In our initial experiment, we tried to find the wavelength of the microwave. After repeating our experiment for many times, our results are not constant. So we started to doubt that the standing waves may not be as simple as we think—they mightpossibly be several three dimensional waves which are very hard to visualize. It is not possible to always get a distance of six centimeters between two burnt points, such a case has been repeated by many people in their videos online. We started to doubt the reliability of the videos although they can always get the correct answer for wavelength of light. After consulting our teacher mentor, we concluded that the standing waves inside are 3 dimensional. Also we decided to try to map out the 3 dimensional waves by putting different materials inside. 

Materials considered


To map out the standing waves of the microwave. an object can be placed inside the oven and from there, the hot spots can be identified. However a suitable object must be used. It must:

1: absorb microwave: most preferably an object that contains water as water can absorb microwave well and its common, not reflecting any microwave

2: Common/ easy to find, can be found in the household

3: Affordable

4: Not flammable

5: Do not heat up so fast to the extent that no results can be recorded. 

After much thought, the group found that agar gel may be a suitable material. 

Material used and steps to conduct experiment


Agar gel experiment materials
a)     Rectangular acrylic mould (27cm x 26cm x 1cm)




   b)     10 Acrylic base support*
                                      i.        2cm  x 20cm x 0.8cm (quantity: x2)
                                     ii.        4cm  x 18cm x 0.8cm (quantity: x2)
                                    iii.        6cm  x 16cm x 0.8cm (quantity: x2)
                                    iv.        8cm  x 14cm x 0.8cm (quantity: x2)
                                     v.        10cm  x 12 cm x 0.8cm (quantity: x2)

                * The bases can be rotated to raise the agar to a higher level. For example the            
                  2cm  x 20cm x 0.8cm acrylic base support can be the 20cm  x 2cm x 0.8cm acrylic
                  base support. Meaning it can raise the agar gel 2cm above or 20cm above.
b)    Hot plate
c)     Wok
d)    Ladle
e)     Microwave oven
f)     Pure powder agar gel (swallow globe brand)


To make agar gel
Step 1: Pour 5g of powder agar gel and add 500ml of cold water
Step 2:  Stir constantly in the wok until it boils

To study the microwave in the microwave oven using agar gel
Step 3: Pour the cooked agar gel into the acrylic mould and allow it to cool and harden
Step 4: Put the mould into the oven by using the 2cm x 20cm x 0.8cm acrylic base to support it. Turn it to medium power and heat it for 2.5 minutes.
Step 5: Record the results
Step 6: Repeat steps 1 to 5 with the rest of the acrylic base support listed in b.

The purpose of this experiment is to discover the different patterns the microwave oven makes at different heights. In this way we can find the shape of the 3 dimensional microwave by stacking all the layers of the different height up. Since the oven have a height of 21 cm, and the height of the mould is 1cm, the highest it can go will be 20cm.   

Results of agar experiment




 


 



18x20


1.     Continuing with the steps in the experiment, we went on to raising the acrylic tray up to 18cam and 19cm. The agar gel couldn’t be raised to 14cm and 16 cm as the microwave have a bump in the 14cm and 16cm mark that looks something like this:


Hence we can’t align the tray properly due to the bump as it would be slanted, affecting out results. Therefore we skipped both of the height for now. We would be making a smaller acrylic tray for the next batch of experiment. 

After repeating all the experiment steps for all the experiment, clear plastic sheets were used to mark out the hot spots. 




2cm

 4 cm 


6 cm


8 cm


                                                                             10 cm



12 cm


18cm


19+cm





Analysis of experiment


Analysis of this set of data: This batch of experiment is not reproducible as the experiment when repeated were not consistent. For example when repeated the experiment by raising the height of the agar to 10 cm in height, the dark spots appeared somewhere else. This is not a good sign as it meant that the results are not reproducible as they are not consistent.  The conclusion is the material we used may not be that suitable in the experiment. 





The results were also plotted onto a graph:



The distances are spread over a large range, which shows that the experiments are not reproducible as the spots were randomly found. 






Experiment going towards another direction

Asthe agar gel experiment is not reproducible another material must be used to replaced them. We have come out with a few materials to replace the microwave oven:

 a)      Popcorn
       May not work as it would be hard to measure the distance between two spots

       b)      Crayon
As it is made from wax, it does not absorb microwaves. Lead shavings can solve the problem. So far we have not tried it.


 c)  Hair gel
Hair gel absorbs microwave and it turns into a shade of darker pink when placed in the microwave. 



The small blob of gel was pale pink but the big blob of gel which is placed in the microwave oven changes from pale pink to pink

The results were also quite consistent. After conducting a trial experiment for a few times (readings were not recorded), the spots on the hair gel was found approximately on the same location( without smoothing the bumps but was left to cool) 




However, when we re- smoothened the gel, the spots were found on different locations. This may be due to uneven spreading. 


To ensure that the hair gel is spread properly, we would be using a big acrylic sheet of dimensions larger than 26 cm by 26 cm to smoothen the bumps on the hair gel tomorrow. We will continue to put the hair gel into the microwave oven tomorrow. 




d)     Leaves

Does not work as it will catch fire when placed in the microwave oven.


e)     beancurb

This idea hasyet to be tried out



f) water + yeast + flour
This idea has yet to be tried out

If c doesn't work, we would be trying out on a, c, e, f