Search found 474 matches

by joe
Thu Feb 20, 2020 12:11 pm
Forum: Physics Questions
Topic: quantum biology
Replies: 1
Views: 9305

Re: quantum biology

" I am looking for a physics student to meet with and discuss about this paper. " One of the earliest (perhaps the first) paper indicating quantum coherence involvement in photosynthetic systems was published by a team including researchers from UNSW Physics: https://www.ncbi.nlm.nih.gov/p...
by joe
Fri Sep 20, 2019 8:57 am
Forum: High School Physics
Topic: Heisenberg's Uncertainty Principle vs Emission Spectra
Replies: 3
Views: 15791

Re: Heisenberg's Uncertainty Principle vs Emission Spectra

As far as I know, the "electron cloud" doesn't have a well-defined meaning. It is often used as a metaphor for the wave function.
Often, the wave function is independent of time.
by joe
Tue Aug 13, 2019 10:02 am
Forum: High School Physics
Topic: Heisenberg's Uncertainty Principle vs Emission Spectra
Replies: 3
Views: 15791

Re: Heisenberg's Uncertainty Principle vs Emission Spectra

Yes, the Bohr model is wrong, so it should only be taught as an example of a historical dead-end. The 'cloud' is a metaphor describing the wave function. The electron state changes with the emission or absorption of a photon so, in that 'cloud' metaphor, the electron cloud has a different shape befo...
by joe
Mon Aug 12, 2019 3:04 pm
Forum: Physics Questions
Topic: Pi due to masses of the order of 10 bouncing off each other
Replies: 1
Views: 5955

Re: Pi due to masses of the order of 10 bouncing off each other

The video you linked has fairly detailed explanations. The problem is set up by collisions in classical physics, but it quickly becomes a couple of interesting problems in maths. For insight into the physics, see the Momentum chapter on Physclips http://www.animations.physics.unsw.edu.au/mechanics/c...
by joe
Sun Jul 14, 2019 11:26 am
Forum: Physics Questions
Topic: Percussive Shock
Replies: 1
Views: 9246

Re: Percussive Shock

The link about centre of percussion is good This concept is applied to objects (like bats) that rotate before collisions. The TV show link in principle involves a rotating lever and a collision, but the shock in the man's hand is probably not the prime consideration, so we needn't consider the centr...
by joe
Thu Jul 04, 2019 9:59 am
Forum: High School Physics
Topic: Photocurrent
Replies: 2
Views: 6006

Re: Photocurrent

Why does photocurrent plateau with voltage in photoelectric effect? Good question. As voltage increases, the electric potential energy of the ejected electron will increase. Thus by the time it reaches the anode its velocity will be dependent on voltage. Correct. Ie more will reach the anode per un...
by joe
Wed May 22, 2019 9:28 am
Forum: High School Physics
Topic: Transformer ideal if wires have resistance?
Replies: 8
Views: 26853

Re: Transformer ideal if wires have resistance?

Can a transformer be considered ideal if we don't assume the wires to have no resistance? No. Further, even if the wires are superconducting, there are usually very significant losses due to hysteresis in the core—see the earlier discussion on that. Can the formula 'Power in = Power out' be used if...
by joe
Tue Apr 16, 2019 8:55 am
Forum: Physics Questions
Topic: Fault condition
Replies: 1
Views: 6247

Re: Fault condition

A fault may be a short circuit, which has a low reactance and may draw a dangerously large current.
by joe
Wed Feb 13, 2019 8:06 am
Forum: Physics Questions
Topic: Inertia in Linear and Rotational motion?
Replies: 21
Views: 35136

Re: Inertia in Linear and Rotational motion?

What if define any mass by Inertia, not how it does now Inertia by mass? In other words, change a general method to model systems. Just thoughts.
For many people, inertia and mass are synonymous. To avoid potential ambiguities, I usually avoid the term 'inertia'.
by joe
Wed Feb 13, 2019 8:04 am
Forum: Physics Questions
Topic: Inertia in Linear and Rotational motion?
Replies: 21
Views: 35136

Re: Inertia in Linear and Rotational motion?

Moment of Inertia is not applied in Linear motion at all, if I don't mistake. If it is so, why isn't Moment of Inertia applied in Linear motion? It is not included in the linear motion of a particle , because particles have no extent, and so cannot rotate. If a macroscopic object is travelling in a...
by joe
Mon May 29, 2017 8:53 am
Forum: Physics Questions
Topic: Electrons and Gravity?
Replies: 3
Views: 8236

Re: Electrons and Gravity?

If your definition of a particle is something that can be seen with the eye or photographed with an ordinary camera, then yes, an electron is not such a thing. In physics, particles have well defined position, moment and trajectory. Waves have well defined wavelength and frequency. I think that all ...
by joe
Sun May 28, 2017 12:13 pm
Forum: Physics Questions
Topic: Electrons and Gravity?
Replies: 3
Views: 8236

Re: Electrons and Gravity?

A direct measurement would be a very difficult experiment, because the gravitational effect is so small and any stray electric or magnetic effects so large. However, lots of indirect experiments have been made to look at possible different gravitational effects on n, p and e. Suppose that you measur...
by joe
Thu Dec 29, 2016 7:53 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20816

Re: Electricity and electric current?

If there are no charges present, then yes, an electric field can propagate at the speed of light. But your pieces of wire have charge in them. To change the voltage of a piece of wire, you need to transfer charge to its surface. The inverse ratio of those is the capacitance (C = Q/V). To transmit th...
by joe
Mon Dec 12, 2016 10:23 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20816

Re: Electricity and electric current?

The single wire has a (very small) capacitance per unit length. (In other words, you need to put a tiny static charge on it to raise its voltage. That tiny charge ends up on its surface.) It also has a (very small) inductance per unit length. (In other words, when you change the current, you change ...
by joe
Fri Dec 02, 2016 8:49 am
Forum: Physics Questions
Topic: Electricity and electric current?
Replies: 17
Views: 20816

Re: Electricity and electric current?

There's a subtle point here. Before you close that switch, the left hand wire is at 10V, the RH wire at 0 V. A ms after you close it, the LH wire is at 10 V (bottom) and 5 V (top), varying smoothly between the two. The RH wire is at 0 V (bottom) to 5 V (top). (There is also a current flowing through...