In this lesson
you're going to learn about charge. Before we start, here's a quick
question for you.
Q1
Have you ever used
charge? Click on your answer.
You are using charge now, believe it or
not.
These lessons have been designed to be read electronically,
not on paper.
To read them electronically means using a monitor.
A monitor uses charge to make the screen emit light of
various colors, and to control that light so that it forms letters and windows,
etc.
To produce the
light that the monitor emits, and to control the appearance of that light,
voltage is used to control the path of charge that is emitted at the back of the
monitor and which strikes the monitor screen.
A caveat! If you are reading this lesson using a flat
panel display, then these statements are not true. In that case imagine
that you are using a CRT monitor.
Here is a little pictorial model of what happens.
Click the appropriate phrase to show how the electrons (which carry charge!)
move up, move down, or travel a flat path. Note the following:
When there is positive charge on the top plate there is
also negative charge on the bottom plate. The electron is simultaneously
attracted to the positive charge and repelled by the negative charge.
The same attraction/repulsion is obtained when the charges
are reversed.
Here is what happens.
When you want a dot in the top portion of the screen
you put positive charge on the top plate and negative charge on the bottom
plate, and the positive charge attracts the electrons and the negative charge
repels the electrons as they fly by so they hit the screen above the center.
When you want a dot in the bottom portion of the screen you
put a positive charge on the top plate and a negative charge on the top plate to
repel the electrons, moving them lower.
With no charge on the plates, the electron travels a flat
path.
Here are a few
questions for you to answer.
Q2 If there is more positive
charge on the top plate, which way will the charge move?
Q3
If the moving charge is positive, which way will it move compared to the
direction the electron moves?
Don't get the
idea that monitors are the only devices that use charge. Let's review a
few other places where you may have used charge.
You may have spoken of charging your car battery - or
charging any other re- chargeable battery. Charging a battery is doing
exactly what the phrase says. When you charge a battery you are putting
charge into your battery, and the battery stores the charge for later use.
When you discharge that battery you are also using charge.
Charge flows through the devices you attach to your battery - the lights in your
car, the electronics that control your car, the CD player you put the charged
batteries into, etc.
You use charge
all the time. You may not think about it much, but you do. Here are
some examples of times when you use charge.
Every time you run electronic gear - a TV, a stereo, a
computer - from an AC wall plug outlet, you use a device called a power supply
that stores charge in a capacitor. That stored charge allows the
electronic circuits you use to run during the very short times when the AC
voltage goes through zero - and it does that 120 times a second on a 60hz power
line.
You not only use charge, but charge should be feared - at
times. When clouds get charged they can discharge by producing large
lightning bolts that are very destructive.
Charge affects
everything!
When there's a solar flare, the sun emits a stream of
charged particles that pour down on the earth at a million miles per hour.
A flare can disrupt satellite communications affecting the whole world.
Comets have a tail of charged particles and provide one of
the most awesome sights in the heavens.
What Do You Need To Learn About
Charge?
There are
many things that you might need to know about charge. Here is a partial
list.
Two charges can interact and produce forces on each other.
That effect is used when we deflect a stream of electrons to produce spots at
different points on a monitor screen. The same process occurs in ink-jet
printers. You need to learn about forces between charges.
You need to learn about how charge flows. Remember,
it flowed into the battery and out of the battery. Charge flow is
important.
You will need to learn about units for charge and charge
flow, and you will need to learn about charge related energy concepts like
voltage.
Goals For This Lesson
This lesson
introduces you to some simple concepts about charge. At the end of the
lesson, you want to be able to do the following.
Given
a question involving charge
Be
able to compute amounts of charge.
Be
able to predict how charge moves - when charges attract and when they repel.
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