Search found 474 matches

by joe
Fri Dec 02, 2016 8:14 am
Forum: Physics Questions
Topic: Double-slit experiment revisited....again....
Replies: 16
Views: 19998

Re: Double-slit experiment revisited....again....

We've now put a video of an experimental demonstration of Young's experiment with single photons. It's at http://www.animations.physics.unsw.edu.au/light/interference/index.html#4.6 The introduction to Young's experiment itself and to the nature of light are at http://www.animations.physics.unsw.edu...
by joe
Fri Dec 02, 2016 7:39 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20876

Re: Electricity and electric current?

Metals have the property that the outer electrons are 'shared' among all the atoms: they can move easily.
In insulators (like most plastics) the electrons are 'tightly bound' to their atoms. So they do not conduct electricity (at least not until the field reaches many MV per metre).
by joe
Wed Nov 30, 2016 11:15 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20876

Re: Electricity and electric current?

The potential difference (and thus the field) is initially across the switch. It then very quickly spreads long the wires until, in steady state, there is almost no PD across the switch and it is all across the wires (and the internal resistance of the battery, probably negligible if the wires are k...
by joe
Wed Nov 30, 2016 9:56 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20876

Re: Electricity and electric current?

the difference in electrical potential produces a field and that is what moves the electrons.
Initially, this PD is across the switch.
After switch closing, the PD very rapidly spreads along the wire.
I've given a more detailed description above.
by joe
Wed Nov 30, 2016 9:16 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20876

Re: Electricity and electric current?

Do I understand you correctly that you write that the electric field in the portion of the wire connected with the battery anode (negative lead) has already existed before switching on (my drawing)? No. I wrote: With the switch open, the wire on one side of the switch is at 10 V, and on the other i...
by joe
Wed Nov 30, 2016 8:14 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20876

Re: Electricity and electric current?

With the switch open, the wire on one side of the switch is at 10 V, and on the other it is zero. So 10V potential difference is across the switch. Just before the switch contacts touch (distance ~ µm), the field is large enough to ionise air, so a spark allows current to flow. This changes the pote...
by joe
Sun Oct 16, 2016 6:20 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Discussion of Integral calculus

Yes, I changed the title of the thread. I don't think we have uncovered a paradox.
Joe
by joe
Mon Oct 10, 2016 11:14 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

Actually, based on your performance in the MOOC, I think that you are smart.
What this argument seems to be about is the definitions of limits, and some (understandable and common) misunderstandings about the use of 'to infinity' and 'to zero'.
by joe
Mon Oct 10, 2016 9:46 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

You ask What is F? When I wrote Limit of f(h) goes to F as h goes to zero F was the value of the limit of f(h) as h goes to zero. When we say "The derivative of f(x) is g(x) ", we mean The limit of {f(x+h)-f(x)}/h goes to g(x) as h goes to zero. And by that we mean (quoting from above): fo...
by joe
Mon Oct 10, 2016 9:03 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

That's why you have to be careful with limits and the language you use. The limit of N*(1/N) as N goes to infinity does not mean infinity times zero. It is not adding zeros. When we say "Limit of f(h) goes to F as h goes to zero", we define this to mean: for any epsilon, however small, we ...
by joe
Mon Oct 10, 2016 8:36 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

summing as many zeros as possible results in zero. Consider the expression (Sum N terms) each of which is (1/N) Now, what about the limit of N*(1/N) as N goes to infinity? Would you like this to go to zero? Boris, it's very important to realise that, taking such limits, we are NOT adding zeros. The...
by joe
Tue Sep 27, 2016 2:24 pm
Forum: Physics Questions
Topic: (general)Is Searl Effect Generator real? Anyone?
Replies: 11
Views: 34158

Re: (general)Is Searl Effect Generator real? Anyone?

sounds like a classic outtake from the legacy of a Michael Faraday homopolar, or unipolar, disk/motor/generator. Homopolar generators and motors are described here on our Physclips site http://www.animations.physics.unsw.edu.au/jw/homopolar.htm Just to be clear, homopolar generators and motors do w...
by joe
Tue Sep 20, 2016 11:08 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

Or, to put it another way, it is quite possible to integrate discontinuous functions, such as
y = 0, x < 0 and
y = 1, x >= 0.
by joe
Sat Sep 17, 2016 11:48 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

But in your post of Mon Sep 12, 2016 6:22 am,
h is dummy variable, inside a limit statement, while delta x is a quantity that multiplies the limits. These are defined very differently.
Joe
by joe
Wed Sep 14, 2016 10:15 am
Forum: Physics Questions
Topic: Discussion of Integral calculus
Replies: 116
Views: 92140

Re: Fundamental paradox of Integral calculus?

We cannot divide nothing by nothing and get some slope
Agreed, and so we don't do that. Instead, to take a derivative, we look at the ratio delta y/delta x and examine its limit for small delta x.