Set the meter (M5) to the 1A setting and turn on the switch (S1). The
lamps light and the meter measures the electric current flow. Try
rearranging the parts in the circuit (keeping the “+” side of the meter
aligned with the “+” side of the batteries) and how it affects the circuit.
Next, try replacing any of the lamps (L4) with the press switch (S2)
and push it.
This circuit has the lamps connected in
a series (not in parallel, as in project 5).
This arrangement makes the lamps
dimmer because the battery voltage is
divided among the 3 lamps, but also
makes the batteries last longer
because less current is flowing.
Electricity from the batteries flows in a
loop, equally through each component
in the circuit.
Rearranging the components in a
series circuit does not change it,
because the same amount of electricity
is flowing through each component.
Replacing one of the lamps with the
press switch increases the current,
because the pressed switch has no
resistance to the flow of electricity.
If several lamps are arranged in series
and one burns out, none will work
because the only path for electricity is
blocked.
Project 8
Fast Brig t, Slow Dim
Incandescent light bulbs, like those in the L4 lamps, make
light by passing a big electric current through a special
resistive wire (the filament), which gets so hot that it glows.
The two left bulbs (A & B) get less current than the right bulb
(C) so they take longer to heat up and don’t get as hot.
The meter measures the voltage cross left lamps A & B.
This voltage will be low when the left lamps are dim. When
you remove lamp B, both remaining lamps have the same
voltage across them and the same current through them.
In part A, you might have expected left lamps A & B to be
half as bright as the right lamp (C), because the current
through lamp C should divide equally between lamps A & B,
but instead lamps A & B are much dimmer. This occurs
because bulb filaments offer less resistance to the flow of
electricity when they are cold, and increase in resistance as
they heat up. Your L4 lamps have resistance of less than 5
ohms when they are cold, and about 15 ohms then bright.
1A
5
Project 7 Find Your Own Parts
1A
Build the circuit shown; the can be
anything you want. Set the meter (M5) to
the 1A setting and turn on the switch
(S1). Touch various materials between
the snaps on the 4-snap wire and
batttery holder “—” side. Use the red
jumper wire to help make a connection if
needed. See which materials are good
at transporting electricity by watching the
meter current and lamp (L4) brightness.
If the meter reads zero, switch it to the
1mA setting to see if there is just a very
small current. With the 1mA meter
setting, try placing two of your fingers
across the snaps to see how well you
transport electricity; wet your fingers to
get better electrical contact. To help
protect the meter, always switch back to
the 1A scale before testing a new circuit.
?
?
Part A: Set the meter (M5) to the 5V setting. Push the press switch (S2)
for several seconds, while watching the meter. The meter is measuring
the voltage across the two left lamps (labeled A & B); its reading jumps
up when the switch is pressed, then slowly rises more for a few
seconds. Push the switch again while closely watching the lamps A &
B. Notice how lamps A & B initially are off, but turn on dimly within a
second or two.
Note: The voltage measured in this step will be small; in some cases in
may even be too small to measure with your M5 meter. M5 is a simple
meter, don’t expect it to be as accurate as normal electronic test
instruments.
Part B: Remove lamp B, and push the switch again. Now both
remaining lamps (A & C) get equally bright fast, and the meter shows a
higher voltage across the left lamp (A).
Part C: Replace the right lamp (C) with a 3-snap wire, and push the
switch again. Now the left lamp (A) gets the full battery voltage, as
shown on the meter.
Project 6 Loop
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