Hey !

I was wondering - what excactly make substance A resist less to electricity than substance B ?

Is it because substance A got more "free electrons" , so if a group of electrons hits them , those "free electrons" will abandoned their father atom , while making this "chain reaction" on the other atoms in A ?


Plus , does my theory contradict the new atom theory that says its not an electron around the atom , but probability ?

If anyone can help me with this , or got a site to explain those things (except wiki , didnt find my answers there !) I would be grateful !


Thanks !
Niv

Hi Niv,
Conductors will have an unfilled valence band (outer shell) so that electrons can move from atom to atom easily. Insulators have a full valence band. Resistors mix weakly conductive materials (like carbon) with insulating materials. The more carbon, the lower the resistance. These are just typical examples. Things get really interesting when you look at semi-conductors (which conduct only after the band-gap differential energies are reached) or super conductors (which are typically insulators until a certain low temp is reached and they become 'perfect' conductors). Those are cool.
Peace,
Ron

Hi you all!

Such chain reactions exists in insulators. This is how a sparks appears in air, or how current flows in a high-voltage reverse-polarized diode. This needs a minimum voltage above which the current increases brutally.

The mechanism is different in a metal, where there is no minimum voltage and current increases linearly. This means that mobile charge carriers preexist to any applied voltage.

The origin of resistance is pretty much unclear, as we have no satisfying theory to its absence in superconductors. The number of mobile charge carriers is a factor, their mobility as well. Lower temperatures, better chemical purity, better crystal perfection tend to improve the mobility.

You may read about several models, like the free electrons gas, the band theory and more.

However, I've got the impression that Hall effect measurements coupled with the low heat capacity of metals contradict these models. Or I've understood them badly - very possible.

Mr. Faraday determined that resistance is a function of both structure and valence.

A better question would be - "what causes cryogenic super conductivity."

Gavilan

Gavilan, had you taken time to read more of your book, you would know this was about electrolytes and nothing else.

Thanks everyone it helped me alot !