Download Equivalent Resistance

Circuits
Series Circuits
Big R = Big DV
small R = small DV
Current is the same everywhere
Voltage gets divided up based on the resistance
Parallel Circuits
Current gets divided up amongst the resistors
Voltage stays the same
SERIES
PARALLEL
SERIES
Resistors in Series…just add up
Req  R1  R2  R3
Resistors in Parallel…add the reciprocals
1
1
1
1



Req R1 R2 R3
= 5W
Equivalent
Resistance
These two resistors in
parallel can be calculated
as one resistor
= 1W
= 2W
= 4W
= 3W
1
1
1


R2,3 R2 R3
1
1
1


R2,3 4W 2W
R2,3 = 1.33W
Req = 3W + 1.33W +1W +5W = 10.33W
series
= 10W
parallel
Find the Equivalent
Resistance and Current
in the circuit
1
1

10W 10W
= 5W series
= 10W
I = V/Req = 40.0V/10W = 4A
What is the current through the 2.0W resistor?
equal resistance…the current divides equally
2A each way
= 40W
= 20W
= 40W
= 20W
Find the equivalent resistance and current
through the 20W and 8W resistors
I = V/Req = 12V/40W = 0.3 A
I through 8W resistor = .15 A
What if the resistance is not equal
in each resistor?
12V
6W
2W
How much current is going through the 2W resistor?
Calculate the equivalent resistance…
1/Req = 1/6W + 1/2W = .667W-1
Req = 1.5W
Calculate the current in the circuit I = V/Req
I = 8A
The 6W resistor has 3x the resistance than the 2W, so 3x more
current will flow through the 2W resistor… (2W gets ¾, 6W gets ¼)