circuit notes.cwk

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Ch 35 Electric Circuits Notes
circuit symbols used in schematic diagrams
Resistors can be connected in series; that is, the current flows through them
one after another. The circuit in Figure 1 shows three resistors connected
in series, and the direction of current is indicated by the arrow.
Resistor- an electrical device which offers resistance to the flow of charge.
device where electrical energy is transformed into another form

The type of resistor connection will have a major affect upon the overall
resistance of the circuit, the total current in the circuit, and the current in
each resistor
pt. A
Series Circuit
pt. B
Parallel Circuit
all devices connected one after the other all devices connected at same 2 pts to voltage source
only 1 path from the ends of batteries each device has its own path from ends of batteries
a single pathway for charge flow multiple pathways for charge
thus current thru ea. device is same
total current divides b/w branches
I = Vbattery / R total Rtot increases I = Vbattery / R total Rtot decreases
Icircuit = I1 = I2 = I3 Icircuit = I1 + I2 + I3
Ohm’s law applies sep. to ea. device Ohm’s law applies sep. to ea. branch
-current for ea. determined separately
-current for ea. determined separately
-amt. of current in each ~ 1/ R device -amt. of current in each ~ 1/ R device
-Δ voltage across each decreases -voltage in each device same (all connected
-current across each bulb doesn’t Δ
to same voltage source @ same 2 pts)
(same ratio of ΔV to R I=ΔV/ R)
unscrew 1 bulb > others go out
if current is cut to one; it is cut to all
unscrew 1 bulb > others stay on
increase # of resistors/devices/bulbs: increase # of resistors- adding more branches
chg slows down thru each more paths for charge- flow speeds up
decreases overall resistance> increases current
decreases overall circuit current increases overall circuit current
bulbs get dimmer
bulbs get brighter
Questions of concern comparing and contrasting series & parallel circuits:
1. As the number of resistors (light bulbs) increases, what happens to the overall current within the
circuit Intensity of each bulb
2. As the number of resistors (light bulbs) increases, what happens to the overall resistance within
the circuit
3. If one of the resistors is turned off (i.e., a light bulb goes out), what happens to the other resistors
(light bulbs) in the circuit Do they remain on (i.e., lit)

Parallel Circuits
The study of the overall current for parallel connections requires the
addition of an indicator bulb. The indicator bulb is placed outside of the
branches and allows one to observe the affect of additional resistors upon
the overall current
With each increase in a branch with a light bulb, the overall resistance for
the circuit drops. There are more options for the charge to flow, actually
increasing the rate of flow of charge (increasing the current!)
all devices connected at same 2 pts to voltage source
pt. A
pt. B