20-1 Schematic diagrams and circuits
• Schematic diagrams use standardized symbols to summarize
the contents of electric circuits.
• A circuit is a set of electrical components connected
so that they provide one or more complete paths for the movement of charges.
• Load – something in the circuit that uses up electricity
(i.e. bulb, motor)
• Closed circuit – the circuit makes a continuous loop
with no interruptions
• Open circuit – there is a break in the circuit and
current does not flow
• Short circuit – when a circuit path contains little
or no resistance; can cause damage/fire
• Any device that transforms nonelectrical energy into
electrical energy is a source of emf.
• If the internal resistance of a battery is neglected,
the emf can be considered equal to the terminal voltage.
• Know the symbols on p. 731.
20-2 Resistors in series or in parallel
• Resistors in series – the equivalent resistance is
equal to the sum of the individual resistors.
• Req
= R1 + R2
+ R3 + …
• Resistors in series have the same current flowing through
all of them.
• Resistors in parallel
1/Req
= 1/R1
+ 1/R2
+ 1/R3
+ …
• The current produced by the emf source is divided into
the different paths.
• I = I1
+ I2 + I3
+ …
• If the resistors in parallel are equal, the current
is evenly divided.
• Resistors in parallel have the same voltage across
them.
• Not all paths in a parallel circuit have to be closed
for other parts to conduct electricity.
20-3 Complex resistor combinations
• Most electrical devices use a combination of series
and parallel resistor circuits.
• To obtain the resistance of a complex circuits
- isolate the segments of series
and/or parallel resistances
- find the resistance of each
segment
- combine the resistance of
all segments |
