Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 41)

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If you wrap two wires from different circuits around
different ends of an iron bar then a current flowing
through the wire from the first circuit will magnetically
create a current in the wire from the second circuit! If the
second coil has twice as many turns (more magnetic
linkage) as the first coil then the second coil will have
twice the voltage but half the current as the first coil. A
device like this is called a transformer. Your Electronic
Playground includes one. It consists of a 300mH coil, with
a middle tap point allowing use as two connected 150mH
coils, and a 3mH coil wrapped around an iron bar. In
Experiment 17 we used the 300mH coil by itself but
usually it will be used to drive a speaker, which needs a
high current with low voltage. The symbol for a
transformer is shown on the right: The magnetic field created in an iron bar by an electric
current in the coil around it can be harnessed if the bar is
allowed to rotate - it is a motor. It could be used to drive
the wheels of a car, for example. The reverse is also true,
if a magnet within a coil is rotating then an electric
current is created in the coil - a generator. These two
statements may not seem important to you at first but
they are actually the foundation of our present society.
Nearly all of the electricity used in our world is produced
at enormous generators driven by steam or water
pressure. Wires are used to efficiently transport this
energy to homes and businesses where it is used.
Motors convert the electricity back into mechanical form
to drive machinery and appliances.
It must be remembered that all of the inductance
properties discussed here for coils and transformers only
apply to AC (alternating current). For DC, inductors act
as wires with no special properties and transformers are
just two separate, unconnected wires.
Transformer
Symbol for
Transformer
1. A diode has very high resistance when it is
__________-biased.
2. Diodes whose turn-on energy is so high that light is
generated are known as __________.
3. The transistor is best thought of as a current
__________.
4. An __________ circuit is one that might have many
resistors, diodes, capacitors and transistors on a
single piece of silicon.
5. A transistor is __________ when the circuit
resistances, not the transistor itself, are limiting the
transistor’s collector current.
6. Inductors have low resistance to __________ current
and high resistance to __________ current.
7. Adding inductors in parallel __________ the
inductance while adding inductors in series
__________ the inductance.
8. Electrons not only have electric properties but also
__________ properties.
9. Wrapping a coil around an iron bar __________ the
inductance.
10. If the second coil in a transformer has half as many
turns as the first coil, then the second coil will have
__________ as much alternating current as the first
coil.
(Answers are on page 5).
TEST YOUR KNOWLEDGE #2