Ron, doesn’t Dave need a couple of other bits of information / clarification in order to calculate the answer?
Andy
Yes, the number per second
A couple of videos from Brian Cox on the subject
And a second one on Black Holes, where he describes the singularity as more a moment in time rather than a place in space, given how warped space/time is.
i remember going to a brian cox show a year or two ago all about black holes. His mate / presenter who brings him on warned us that you won’t remember anything he says after tonight, and he was bob on. It was a facinating talk and he makes it all sound sensible and understandable but I havent a clue what he said or anything about the night 
In case anyone is actually interested, the back of the envelope: (i.e. not worrying about a few of the details asked above)
1uV into 50 ohms is 1e-12/50 = 2e-14 watts = J/sec
photon energy e = h nu = 6.6e-34 * 7e6 = 4.62e-27 J/photon
so you need to capture 4.3e+12 photons/sec.
Your shotnoise floor would be ~2e6 photons/sec or 6.8e-4 uV, so you would have some overhead before hitting that fundamental limit. That’s typically the reference for when “quantum” phenomenon start to become more noticeable.
Amazingly, I got a very similar final answer as you but via a more long-winded process. I calculated immediate variables at the antenna: electric field strength & power density of the signal, effective area of the dipole, and total power captured by the antenna.
Probably some redundant steps but a useful exercise for me to understand the relationship between a radio signal and its interaction with the antenna.
One of the most important things I learned in physics was the principle of least action. Don’t do a full analysis if an order of magnitude estimate will do it for you. Although in this case there energy arguments should get you there! I suspect you learned more in your calculation than I did, however.
I’m all for least action.
Now I’ve seen your method it’s obviously the quickest route to the solution as the question as posed gives us the voltage (1uV) induced in the (unloaded) antenna by the incoming signal, so it’s just an electrical calculation (voltage, impedance, power, etc).
I suppose I was thinking about what RF signal would be needed to produce that voltage – redundant in this case.
I enjoyed the exercise and have learnt (or re-learnt) stuff about that fascinating interface between radio signals and antennas.
Whenever I hear someone say “speed of light” in the back of my mind the lyrics to Queen’s 1978 hit song “Don’t Stop Me Know” jump into my mind. There’s a refrain where Freddie Mercury sings
“I’m travelling at the speed of light,
I wanna make a supersonic man outta you”
Fair enough both lines suggest incredibly fast travel.
But it’s the line before which has irritated me for nearly 50years.
“Two hundred degrees, that’s why they call me Mister Fahrenheit”
What’s that rubbish meant to mean? If it was two hundred and twelve degrees, then yes Mr. Fahrenheit would be OK. But 200 is a nothing special temperature!
And so as we deal with speed of light, it’s time for someone, me, to introduce Cerenkov Radiation where you get stuff travelling faster than the speed of light giving the cool blue glow seen when radioactive materials are stored under water.
I assume if we take wave particle duality to extremes it ought to be possible to work out the wavelength of an activator….
For light hearted but interesting listening the BBC podcast Curious Cases is worth a shot. This episode seems relevant.
There’s also one about why a pint of beer in space is the shiniest object in the universe.
Photons suffer the same problem as when we drive in traffic. In ‘free space’ they always go at the cosmic speed limit we call “c” but it’s those annoying delays being absorbed and emitted by matter they meet on route that extends the total journey time. [Pedants will point out it’s not the same photon but a series of photons, a bit like a baton relay race]. People are usually surprised by how slow light travels in liquids and solids.
I find it amazing that photons at the core of the sun take 10,000 to 170,000 years to reach the sun’s surface (or rather their descendants do) and then only about 8 minutes to travel 93 million miles into our eyes.
Nothing. It’s a song!
But not faster than c.
I seem to recall that the phase velocity of a wave in waveguide can be faster than the speed of light - but I would need to find the section in the Services Handbook which states this, and I haven’t studied that since 1971 
No, coz we’re not made of photons. But we do radiate photons at infrared wavelengths.
In any case, in macroscopic objects like us (trillions of quantum particles) quantum effects - like resonant frequencies - are cancelled out by interactions (it’s called decoherence).
Yes. Most of my world/career works fine with O-level views of physics. It’s the fact that it’s easy to miss the “in a vacuum” bit of the definition of c.
Still Cerenkov Radiation just looks sublimely like “real sci-fi”.
That’s because phase velocity is just a useful mathematical concept. No information can be carried at that speed.
Freddie was probably just using a round number to fit the lyrics and 200 degrees is hot regardless of if its C or F so mr Fahrenheit is like calling him hot. I guess. I’m not sure he looked into the physics principals when writing the song 
.
good song though.
Freddie may not have been a physicist but the guitarist Brian May is. He had his B.Sc and was doing a Ph.D when he quit to be a rock star!.
It’s as annoying as Jeff Lynne singing “I wish I was a wild west hero” when we all know it should be “I wish I were a wild west hero.” Damn brummy don’t know his past indicatives from his past subjunctives and so he can’t speak proper like what I can and does.
