Transcript 21-8 Applications of Induction: Sound Systems

21-8 Applications of Induction:
Sound Systems, Computer
Memory and the Seismograph
•Some microphones operate with induction…as the
‘plunger’ moves deeper from sound waves striking
it, as the coil moves, voltage is produced.
•Recording and playback in magnetic tape uses
induction. (analog)
•Digital induction involves 0 and 1 signals instead of
a continuous variation.
•Movement of the earth can cause a suspended coil
to move in a magnetic field to cause induction and
conversion of that movement to electric current.
21-9 Inductance
• Mutual inductance…If 2 coils are placed
close to one another, a changing current in
one will induce a current in the other one.
E=-M (DI1/Dt)
• Inductance has SI units of henrys
• 1H=Vs/A=Ws (Joseph Henry)
• The value of M depends on whether iron is
present or not, and on geometry.
• M=constant of proportionality
21-9 Inductance (cont’d)
• Self inductance can occur when a lone coil has a
current that produces a change in magnetic flux,
which causes induction on the coil.
E=-L (DI1/Dt) …
• L=constant of proportionality or self-inductance or
simply inductance.
• Any ac circuit contains some inductance…if there are
many coils then there may be considerable
inductance…often called an inductor or choke coil.
• See symbol on page 639. Winding backwards can
cancel the effect.
21-9 Inductance (cont’d)
• An inductance acts something like a
resistance to impede the flow of
current…we call this impedance.
• Impedance depends on L and on f.
• See Example 21-11pg. 640
21-10 Energy Stored in a Magnetic
Field
• We have seen that energy can be stored
in a capacitor… U=1/2 CV2
• For inductors, energy can be stored…
• … U=1/2 LI2
• See formulas on page 640-641
21-11 LR Circuit
• Any inductor will have some resistance.
• An LR circuit has some properties similar
to an RC circuit.
• See formula and diagrams on page 641.
• See Example 21-12 p 641.