# Home Depot/ Radio Shack speed of light?

#### bblupton

Home Depot/ Radio Shack speed of light???

Is there a way to measure the speed of light, to say 2 significant figures, using things purchased from Radio Shack and Home Depot? I've got a 200' hallway and front surface mirrors. Thanks, Bradshaw

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#### russ_watters

Mentor
I believe Michelson used a mechanical interferometer (a spinning mirror and a prism) in his test. I'm not sure if this is how he did it, but if you vary the rpm of a spinning mirror, you can sync up the outgoing and incoming pulses of light to measure the time. You won't get any better than 1800s era accuracy, but it its a start....is this for a college project?

#### robphy

Homework Helper
Gold Member
I recall a lab experiment using a fast oscilloscope, a function generator, and a laser and detector. (Can you get these at Radio Shack?) Try googling: "speed of light" AND oscilloscope .

#### Crosson

I go to school at a cheap university, we measured the speed of light by setting up standing waves of known microwave frequencies. Google for standing waves.

#### bblupton

Thanks for the standing waves idea. I have a 60,10,3watt watt generator for the 2m and 70cm ham bands. What is the apparatus and method of observing the standing waves? I wonder if 3 watts is too much radiation for students (and me!) Thanks, Bradshaw K1TE

#### Crosson

The microwaves in our experiment had a wavelength of about 10cm (this is what is measured in the experiment). The apparatus consisted of a transmitter and a reciever, the distance between which could be varied. Monitoring the voltage in the receiver can tell you when standing wave patterns occur (when the distance between trans and reciever is an integer multiple of wavelength).

#### mmwave

Crosson said:
I go to school at a cheap university, we measured the speed of light by setting up standing waves of known microwave frequencies. Google for standing waves.
I went to a cheaper university and we use a microwave to make the standing waves and marshmallows as the detector. Incredibly you can do better than 2 sig figs if you know the freq. of the oven typically 2.65 GHz. Google marshmallow speed of light on google & you will find many descriptions of this. Just be sure to use a paper plate and to take the turn table out of the microwave when you do the experiment.

mmwave.

#### bblupton

Thats great! And an edible lab as well! Thanks, Bradshaw

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