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posted Nov 25, 2015, 8:19 PM by Upali Salpadoru

1. Speed of light using Microwave

posted Feb 10, 2015, 4:04 AM by Ranmini Perera
Simon Flynn in his book, “The science Magpie” published in 2012, describes an experiment to determine the speed of light without stepping out of the house.  What you need is only a microwave oven and a suitable food item. (inquiries:  click here)
 

Fig. Stop the rotation; spots appear on food. 

Microwave cooker produces electromagnetic waves which are in the same nature as light. There is an established formula that the velocity (speed) of a wave can be obtained by multiplying the frequency of a wave by it’s wave length.  V = f l    

( V – velocity ,  f – frequency and l - wave length


  The frequency of the microwaves would be given at the back of the appliance. Normally it would be  MHz. This can be converted to Hertz as   2450 X 10 6
After removing the rotating plate place a chocolate bar and awitch on the oven for 15 seconds. Choclate bar will melt at a few spots.


Measure the distance between the spots. Convert this to meters. 
If the measured length was 4 cm conversion will give 0.04 m as half a wave length.
Then the wave length will be  2x 0.04 m  = 0.08 m

As the high heat is at the peaks of the wave the distance between the marks will be half a wave length.  Double this to get the wave length and apply the formula V = fl.    
                                   Velocity =  distance x2 x 2450 000  000 m/s
  If the measured average value is 6 cm     the wave length     will be 0.12m
 Then V =  0.12 x 2450 000 000 m/s
              294 000 000 m/s        which is a fair answer compared with the true speed.


The true speed of light =  299 792 458 m/s                                              

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