Here are some things to do to finish this section.
What question did you think of that could be studied, or
observation could you make that is interesting or unexpected?
Send it to the Question board!
Discuss these questions with the people in your group. Please
send us a discussion of these two
questions. Don't forget to tell us the group name.
Electrical appliances usually have a little placard on the back
or bottom giving their electrical ratings, specifying voltage (V)
and either current (A) or wattage (W) (or possibly both). (It also
tells the frequency (Hz or cycles); this is of less interest to us
at the moment).
Houses have fuses or circuit breakers that act like switches to
disconnect any device that is drawing a current that is too large
-- for example, more than 15 Amperes. The sum of the current
ratings for the devices on a circuit must be less than the circuit
breaker's limit.
Here are some examples:
This label on a heater gives
both current and wattage information.
The label on the bottom of a toaster
Part of the sign on the back of a computer
monitor. It says it can be used in a
100-to-120 V system, and will draw 1.8A, or in a
220-to-240 V system, and then it will draw 1.0 A.
Please make a table of the information for various devices.
(Here is a blank table that you
can print out) Please send us at least part of your table --
the device that drew the most current, the device that drew the
least current, and another one. We are compiling a giant table of
all the values anyone has found.
Judging from your table, what are the implications of a device with
a very large current rating?
Sometimes
switches do more than just connect or disconnect one wire. For
example, a common kind of switch is the "double throw" switch which
connects the wire on the left to the upper wire on the right or to
the lower wire on the right, depending on its position.
Another kind of switch is the "double pole" switch which really is
two separate switches connected so that you turn them on and off
together. (The green line in the picture represents a mechanical
connection, not an electrical connection). This would be useful if
you wanted to turn on both the stove light and the fan at once.
Finally, there are even "double pole double throw" switches.
Here's an oldfashioned version of these three kinds of switches.
You can "throw" the switch to right or left, and the handle may be
connecting more than one circuit at once. In addition to making the
connections, these switches also allow having no connection, as
shown; this would not be a desirable property in the problems posed
below -- let's assume our switches always connect some input to
some output.
Now that you know all about switches, here are some questions about
them, that will give you some practice in reading circuit
diagrams.
You have a
light switch at the bottom of the stairs and at the top of the
stairs, both of which turn the light on and off. Here are some possible
ways to connect the system. Which do you think you have in your
house? Justify your choice
Explain what each of these circuits does.
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If there is something that you don't understand about electrical
current, Ask us!
This is the end of this section. (Check this
box ) The next section is about current direction