Download But back to the first question….

The Physics of
Electricity and
Magnetism
Transistors
9-12 Science Std: Phys 5h
Why have electronics gotten smaller
over the years?
The answer is: transistors
When we talk about transistors….
We first need to talk about electric current
Electricity
is made in
lots of
ways
From
water
power
Or from wind
power
From nuclear or
burning coal or gas
Then the electricity travels….
The current comes to our house…
Where we plug in
and use the
electricity
And we use the electricity
We use it in lots of ways….
To cook our
food
To light the
house at night
To heat up
a snack
And we use the electricity
But you probably use it to run
Your personal
electronics
But we didn’t always have these toys
Electronics have changed over the years
Look at a radio
In the 1920’s
they were
big
By 1940 they
started
getting
smaller
They got
even smaller
in the 1960s
And today….
A radio is even smaller
The smallest radio can fit in the palm – of an ant!
Even your cell phone….
Cell phones have changed as well….
The first cell phones were so large they had to be
carried in a briefcase
Even your cell phone….
Over the years they got smaller too…..
1981
1982
1993
2003
1996
2000
Not only smaller… but
they can do more
things
And why are they smaller?
One reason……..
A tiny electronic device called a transistor
So what is a transistor?
A transistor is an electronic device that can:
1. Control a large
amount of output
current with a small
input voltage
This is how a
radio works
2. Turn a large
electrical signal on
and off with a small
input voltage
This is how a
computer works
How does a transistor work?
First we must review some electrical words:
Electrical Conductor
A conductor is
something that easily
lets electric current go
through it
Like electric wire
Electrical Insulator
An insulator is
something that doesn’t
let electric current go
through it
Like the plastic insulation
on an electric wire
How does a transistor work?
A transistor is something different
It is an electrical semi-conductor
A semi-conductor is
something that
sometimes lets current
flow through it….
And sometimes it
stops current from
going through it
How does a transistor work?
A semi-conductor works something like this……
Think of a semi-conductor like a wall on an
electric current highway that can be moved…
The electric current comes along the conducting
wire and get stopped by the wall
So the semi-conductor is working like an insulator
How does a transistor work?
A semi-conductor works something like this……
When a small electrical voltage called a bias
voltage is applied to the semi-conductor
It is like a small tractor
that pulls the wall off
the road a little bit
When part of the road
is clear, some of the
current can get by and
keep on going
The rest of the current is still stopped by the wall
How does a transistor work?
A semi-conductor works something like this……
Turn off the bias voltage….
And the tractor
pushes the wall back
across the road
With the wall across
the road, all of the
current is stopped
again
How does a transistor work?
A semi-conductor works something like this……
That is how an amplifier works
A small input from a
microphone or a
guitar
Controls a large
current that powers
the speakers that
make the sounds we
hear
How does a transistor work?
A semi-conductor works something like this……
In a computer….
The control is big
enough to move the
wall out of the way
So the current is
either all the way on
or all the way off
But back to the first question….
Why have electronics gotten smaller?
We said it was because
we now use transistors
But why did that make
electronics smaller…..
Before transistors, we
used something called
a vacuum tube to do
the same thing as a
transistor
But back to the first question….
Why have electronics gotten smaller?
Vacuum tubes are very large and they use lots of
energy to work
Look at the
difference in
sizes between
vacuum tubes
and the
transistors on
the far right
But back to the first question….
Why have electronics gotten smaller?
So when you put lots of
vacuum tubes together
It made a very large
machine that used lots
of power and was hard
to use
This is an early
memory card
But back to the first question….
Why have electronics gotten smaller?
How much memory is this?
If you take a floppy disc
It would take over 100
of those vacuum
memory walls to equal
one floppy disc
But back to the first question….
Why have electronics gotten smaller?
So the first computer was huge… The ENIAC
computer filled
several rooms
and did the
same thing as a
pocket calculator
But back to the first question….
Why have electronics gotten smaller?
We replaced this wall of
tubes with a board of
transistors
And things started
getting smaller…..
Boards had 100’s of
transistors on them and
were as big as a text
book
But back to the first question….
Why have electronics gotten smaller?
Then we replaced
boards of transistors
with silicon chips
Things kept getting
smaller
Each silicon chip had
1000’s of transistors
on them
But back to the first question….
Why have electronics gotten smaller?
Now we replace big
silicon chips with even
smaller chips
This is a programmable
memory chip
Each one of these
chips has Millions
and Millions of
transistors on them
Important things to remember…..
Transistors are used in modern
electronics and have made them smaller
Transistors are semi-conductors
that can control a large current
using a small bias voltage
Transistors are amplifiers that
make a large output with a small
input
Transistors are switches that
turn on and off large currents
with a small control current
Your Homework…..
Keep working on
your projects