Elenco Green Projects - Manual (Page 24)

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Project #19 Resistors
Honk Your Horn Project #20
Build the circuit shown. Set the meter (M6) to the 50mA
setting and the slide switch (S5) to position C. The pivot
stand base has 47
Ω and 10KΩ resistors in it. They are
used to control the flow of electricity in a circuit.
Push the press switch (S2) to measure the current
through the 47
Ω resistor; it should be around 50mA.
To measure the current through the 10K Ω resistor,
set the meter to the 0.5mA setting and the slide
switch to position B. Push the press switch to show
the current, it should be around 0.4mA. The current
is much lower this time, because the 10K
Ω is a higher
value resistor.
The meter has internal resistors, which scale the
measurement it makes into the ranges indicated on it.
The 10K
Ω resistor can be used with it to double the
voltage scale to 10V. Keep the slide switch in position
B, set the meter to the 5V setting, and push the press
switch to measure the battery voltage using a 10V
scale (double what you read on the 5V scale).
50mA
The resistance of a circuit represents
how much it resists the electrical
pressure (voltage) and limits the flow of
electric current. The relationship is
Voltage = Current x Resistance. When
there is more resistance, less current will
flow unless you increase the voltage.
Resistance is measured in ohms (
Ω), or
kilo ohms (K Ω, 1000 ohms).
What is Resistance? Take your hands
and rub them together very fast. Your
hands should feel warm. The friction
between your hands converts your effort
into heat. Resistance is the electrical
friction between an electric current and
the material it is flowing through; it is the
loss of energy from electrons as they
move through the material.
Build the circuit, set the meter (M6) to
the 50mA setting. Push the switch (S2)
to “honk” the horn (W1), while the
meter measures the current through it.
Compare the current with the horn to
the current using the LEDs and
resistors in projects 18 and 19.
50mA
The horn converts electricity into sound
energy by making mechanical vibrations.
These vibrations create variations in air
pressure, which travel across the room.
You “hear” sound when your ears feel
these air pressure variations.
See projects 1 & 3 if you need to recharge the battery (B4).