h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: How To Calculate The Speed Of Light In Your Kitchen - A32231549
Author: SWL™ Give a man a fish & he'll eat for a day. Give him religion & he'll starve to death praying for a fish. - U1775547

Can someone check the maths & physics please. This does work.

Does the speed of light in a kitchen differ from elsewhere in the house then?

That was the first thing I wondered about.

D'you know how many times I looked at the title before deciding against changing it?

Actually, if you filled your kitchen with Sodium then cooled the whole room down to -270 Kelvin, then the speed of light would change

How about "How To Calculate The Speed Of Light Using A Lump Of Cheese" ?

Oh, leave it as it is, it certainly made me have a look what it is about.

Forgive me if I'm being stupid - but I'm having problems with the maths of this one...

>>>"So, if we multiply 2450 by 120, we get an answer of 294,000. This tells us that the speed of light is 294,000 km per second."

The units don't add up for me

2450 is Cycles per second
120 is mm

So where does the mysterious km come from?

Doh!

Ignore me - I missed the a few zeros off by forgetting about the "mega" in "megahertz"


Having said that, you are playing a bit free and loose with the units without explaining anything (just forgetting about 6 zeros on one side because they happen to correspond to six zeros on the other side of the equation)

2,450,000,000 cycles per second
120 mm = 0.00012 km

In 1 second, the wave travels 2,450,000,000 x 0.00012km = 294,000 km

I think?

Simulpost - ok, I'll sort that.

Brilliant

I reckon the title is fine - you could always add a footnote someplace saying that in order to measure the speed of light in other rooms of the house you just need to move the microwave.

Meanwhile, you quote the speed of light in a vacuum to six significant figures as 299792km/s at the top of the entry, but then measure the speed of light in air, which assuming you didn't travel all the way to Himalayas with your microwave, means that the actual speed of light is a bit slower (trying to google the speed of light in air is less easy than I expected, but somewhere mentioned the refractive index of air as 1.0008, which would give us a speed as low as 299552 km/s, different in the 4th significant figure).

Obviously no one with a ruler and some cheese is going to do much better than 2 significant figures, but mention of the speed of light in air would still be of interest I would think.

One other question - any particular type of cheese well suited to this experiment? Do you get more accurate results with a finely grated cheddar compared to edam?

Wish I had a microwave now.

vp

"Actually, if you filled your kitchen with Sodium then cooled the whole room down to -270 Kelvin, then the speed of light would change."

i already TRIED that! any other ideas?

Try filling it with black. Black absorbs light completely - stops it dead in its tracks.

Nice, neat entry.

I agree with vogonpoet though, you are really measuring the speed of light in air, so the "actual figure of 299792 km per second" is not strictly correct.

BTW, if you filled the room with sodium, the light would just bounce off and proceed at the same speed in a different direction .

This also works with chocolate (so I'm told).

But not with ants.

Gif

"if you filled the room with sodium, the light would just bounce off and proceed at the same speed in a different direction"...

now he tells me ... ever see what happens when the sink overflows in a kitchen full of sodium? trust me, don't try it.

>>>This also works with chocolate (so I'm told).


You mean you can calculate the speed of chocolate using a microwave and some cheese?

No, he must mean the speed of light in chocolate, which is pretty slow 'cos it gets fat and lazy.

What a truely superb entry! I argee with the speed of light in air thing, but otherwise it's fantastic. One thing you have assumed, however, is that your reader knows that microwaves are a type of light (well EM radiation, but you know what I mean). Might want to explain why the speed of microwaves is the same as that of "light".

Oh, and I the title.



Ugi


PS - I think those talking about -270K, must be have their units twisted, in this universe at least (absolute zero being 0 K or -273 'C).

This is great!

Nothing to say on content, so the boring stuff:

You need a full stop at the very end.
"on a turntable to ratate it evenly through the hotspots" -> "rotate"

I read this a few days ago, but this is just a quick note to say that this is a fabulous idea for an entry, and - even better - it's concise and well written. Well done