Part 2 (2/2)

That's how the battery keeps on discharging

We ed for the lead sulphate is not soluble, as I just told you, and it will coat up that plate until there isn'tthe process to reverse That's e are so careful not to let the discharge process go on too long before we reverse it and charge That's hen the car battery has been used pretty hard to start the car, I like to run quite a while to let the generator charge the battery again When the battery charges, the process reverses and we get spongy lead on the negative plate and lead peroxide on the positive plate

You've learned enough for one day Write o on in my next letter to tell how the audion works

You know about conduction of electricity in wires; that is, about the electron stream, and about batteries which can cause the stream Now you are ready for the most wonderful little device known to science: the audion

LETTER 5

GETTING ELECTRONS FROM A HEATED WIRE

DEAR SON:

I was pleased to get your letter and its questions Yes, a proton is a speck of electricity of the kind we call positive and an electron is of the kind we call negative You ht remember this simple law; ”Like kinds of electricity repel, and unlike attract”

The word ion[2] is used to describe any atom, or part of a molecule which can travel by itself and has more or less than its proper number of electrons By proper number of electrons I mean proper for the number of protons which it has If an ion has ative; if the inequality is the other way around it is positive An atom or molecule has neither more nor less protons than electrons It is neutral or ”uncharged,” as we say

No, not every substance which will dissolve will dissociate or split up into positive and negative ions The salt which you eat will, but the sugar will not If you want a name for those substances which will dissociate in solution, call them ”electrolytes” To make a battery we must always use an electrolyte

Yes, it is hard to think of a smooth piece of metal or a wire as full of holes Even in the densest solids like lead the atoe spaces between the nuclei and the planetary electrons of each atom

I hope this clears up the questions in yourto the vacuum tube By a vacuum we mean a space which has very few atoet, with the bestFor the present let's suppose that we can get all the gas lass bulb

The audion is a glass bulb like an electric light bulb which has in it a thread, or filah the glass so that we may connect a battery to theh the wire If we do so the wire gets hot

What do we ets hot?” We lass bulb and we can feel it But what do we mean in words of electrons and atoms? To answer this we must start back a little way

In every bit of matter in our world the atoases they can move anywhere; and do That's why odors travel so fast In liquidswithout getting out of the dish or above the surface Not all of the away fro out into the air above That is why a dish of water will dry up so quickly The faster theclear away fro the liquid makes its molecules move faster and so more of them are able to jump clear of the rest of the liquid That's e coet warm The water in them evaporates ” is speeding up the et very far away fro back and forth and around and around The hotter the body is, the faster are itsGenerally they move a little farther when the body is hot than when it is cold That means they er when hot than when cold It expands with heating because its htly farther

When a wire is heated its molecules and atoms are hurried up and they dash back and forth faster than before Now you know that a wire, like the filaets hot when the ”electricity is turned on,”

that is, when there is a streaet hot? Because when the electrons strea like rude boys on a crowded sidewalk The atoms have to step a bit more lively to keep out of the way These rowing hotter

That is why an electric current heats a wire through which it is flowing Nohat happens to the electrons, the rude boys who are dodging their way along the sidewalk? So so fast and so carelessly that they will have to dodge out into the gutter and off the sidewalk entirely The oing the e off the sidewalks

The greater and faster the strea through the wire, the more electrons will be ”emitted,”

that is, thrown out of the wire If you could watch the out of the wire, here, there, and all along its length, and going in every direction The nue until they have stirred things up so that the wire is just about red hot

What becoet very far away froain They scoot off the sidewalk and on again just as boys do in dodging their way along Soood

If the wire is in a vacuuet very far away Of course there is lots of roo so fast that they need round than do the little tots By and by there gets to be so e each other and so back into the hile new electrons are shooting out fro back into the wire each second as are being emitted from it the vacuuht say it is ”saturated” with electrons, which et out of the filao back inside Or else they have got to be taken away somewhere else

What I have just told you about electrons getting away from a heated wire is very much like what happens when a liquid is heated The et away fro heated the liquid et far away and very soon the space between the surface of the liquid and the cover gets saturated with them Then every time another molecule escapes from the surface of the liquid there oes back into the liquid There is then just as much condensation back into liquid as there is evaporation fro they put covers over the vessels when they don't want the liquid all to ”boil away”