TSR Physics Society

Hey everyone, I would be very grateful if someone could answer my question - why do Copper wires have lower resistance than those made out of Iron? Also, is Copper a chemically reactive element? I posted one of these questions a while back and received no reply. Currently studying Physics at AS Level...

Thank you!

First question: Let's do this the "AS" physics way.

Because we only concern metals here, so I am not going to mention semiconductors and insulators.

Resistance of metal is mainly due to the "vibration" of metal ions arises from thermal energy, which will cause a destructive interference with the electron waves (recall wave-particle duality), and thus the electrons carry less energy so there is resistance.

Different metal ions have different size, different amplitude of vibrations and probably different frequency in same temperature, so different metal has different resistance.

Second question: It really depends on how you define reactive. It is not the upper half in the metal reactivity series so I won't consider it reactive.

Is alevel physics difficult?


This was posted from my iPhone: Chat with me on Skype! Search: jj.teh

There is an inconsistency in my consideration in terms of nuclear fission and the discovery of plutonium: In a nuclear fission a nucleus can be shot with neutrons and so the nucleus is divided. New nucleuses emerge which are new atoms after nuclear fission. During the fission, the energy is released.

And now I want to compare this procedure with the discovery of Plutonium: Plutonium was discovered after Uranium was shot by Deuterium (heavy water) in 1940. I looked at the PSE to find out the atomic numbers of Uranium and Plutonium. Uranium has 92, whereas Plutonium has 94 as atomic number. And that is the point which make me confuse: Normally, the products (new atoms) after a nuclear fission have a lesser atomic number than Uranium. But in this case the number of Plutonium is higher than the one of Uranium. Could it be that it came to a fusion between Uranium and Deuterium instead of a fission?

It is fusion. However, to turn Uranium into Plutonium you have to put more energy in than you get out.

I see. The energy is highest during the fusion and then the energy decreased step by step. That is to say that an exothermic reaction initiate the fusion. Am I right? then thermal energy as one of the reaction product must be emerged, right?

I thought it was that the energy is required for a larger total mass of the product and that the energy gives out as byproduct is actually from the strong interaction.

*As Uranium and Deuterium coalesce, their energy have to increase to enable the bond.

As far as I know bonds are only possible, if the energy of reactants (or one of them at least) is increased.

(...) after all, this is not a chemistry thread.

You are right, I wander from the subject. Another question: All kinds of planets and moons in the universe have gravitation. After Newton's law of gravitation, planets like the earth attract a moon and vice versa. In my consideration, the moon would "fall down" to the earth (because of the higher gravitation), if the moon would have not a centrifugal force to keep the orbit, right?

Based on this view, I think about the sun. Could it be that the Sun apply a gravitation to the planets and the planets to the sun? then the planets apply a centrifugal force to keep the solar system.

I have difficulties with the definition of gravitational potential. To be exactly I didn't understand what it means in practice. Anyone who can tell me the sense of the gravitation potential? thanks!

It is centripetal force. Centrifugal force is a fictitious force due to non-inertial frame.
If the moon does not have tangential velocity as an initial condition, it would indeed collide with the Earth.
(...)

in general if you have a force field the potential is defined as
F=-grad(phi)

I see... in other words: it is just the velocity of the moon in the orbit which pretend that the moon fall down to the earth? then the velocity must expend centripetal force to keep in the orbit, right?

I guess I have got the picture. The gravitational potential is just a physical term, right?
But when this physical term is used? to explain the gravity of an object in a gravitation field?

(...) Note that there is a reaction force of centripetal force on the moon such that it equals to the gravitational force.
(...)

I don't require neither an A-level nor a detailed explanation. I am/was just curious and want to discuss with people who are interest in physics. Strange, eh?

I understand why centripetal force and gravitational force exist in this connection. But I don't understand why reaction force come into being. Would you be kind enough to explain me this connection too?

And then there is another question in terms of astrophysics:
Could it be that the orbits of the planets are inertial systems? In my consideration, the planets have their own (constant) speed in their own orbit to go round the sun. Then the whole solar system would be nothing more than an inertial system.