# Why diode has such a sign?

1. May 24, 2010

### nhrock3

why diode has such a sign??

by the bottom sketch we have the diode to be short circuit

but if we look at the upper sketch we see that the current (ie electrons)
flows from the plus p side

for diode to be short circuit we ned to have the electrons flow to the n side
not to the p side

and i remmember my lessons of basics circuits

they said that the current flows from the big potential to the lower potential
so the electrons move from plus
so if its true the diode cannot be short circuit in that way?

2. May 24, 2010

### mgb_phys

Re: why diode has such a sign??

Conventional current flows form positive to negative, current was invented before electrons.
The simple for a diode is supposed to look like a one-way arrow

3. May 24, 2010

### nhrock3

Re: why diode has such a sign??

so current is not the flow of electrons???

4. May 24, 2010

### nhrock3

Re: why diode has such a sign??

then what flows there?

5. May 24, 2010

### mgb_phys

Re: why diode has such a sign??

Current is the flow of electric charge.
There are two things that confuse people:

1, electrons don't move (much). The electricity flows through a wire at almost the speed of light but electrons only drift a cm/s. The electricty is more like one electron bumping into the next and pushing it, it then pushes the next one and so on.

2, Current was invented before people knew about electrons and people arbitrarily decided it flowed from positive to negative. This is just a convention - like deciding that North is UP on a map.
Now we have discovered electrons are negative and actually flow from negative to positive there is a small problem. in practice this doesn't matter you can just ignore the electrons and use current, or imagine a negative current flowing from negative to positive.
In semiconductor physics we picture a flow of 'holes' which are imaginary positive electrons (or rather the absence of an electron) which do flow in the correct direction.

6. May 24, 2010

### nhrock3

Re: why diode has such a sign??

thanks :)

7. May 24, 2010

### dlgoff

Last edited by a moderator: Apr 25, 2017