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Topic 3 Continued: Resistors
Resistors are used to control the current or voltage in
order to protect other loads in the circuit. They are usually
made from a ceramic core that is coated with a metal, a metal
oxide, a metal film or wire.
Variable Resistor
These resistors have the ability to change their
resistance when exposed to temperature, light, voltages etc.
These are used in many electronic devices like dimmer
switches, fridges, volume controls etc.
Two Types of Circuits
1. Series: They have only one path for all the
current to travel down. If there is a break in the
circuit there is no where else for the electrons to
go so the flow will stop.
2. Parallel: They have multiple paths, (at least
two), for all the current to travel down. If there is a
break in the circuit the electrons will continue to
flow through the other paths.
Wiring
Most residential and commerical circuits are parallel.
•The voltage across all loads in parallel circuits is the
same. If you use an appliance it will not use up voltage for
a different appliance
• Current increases as each path becomes closed. The
current in the appliance closest to the source will increase
as more appliances are turned on.
•More current means temperature increases. If the
temperature rises too high, (too many things are plugged
in/turned on), a fire will start or a fuse will blow, (breaking
the circuit).
Know Chart below (page 291)
Factor
Effect
Length
Resistance Increases as
length increases.
Cross Sectional Area
Resistance decreases as area
increases.
Temperature
Resistance Increases as
temperature Increases.
Material
Some metals allow flow
more easily than others
Read Pages 283 – 291
Complete Designing Circuits Worksheet