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The first step is to find Rt (note that there is no symbol for R1 - the
wire
itself
has resistance!).
Rt = R1+R2+R3
Rt = 1 ohm + 9 ohms + 2 ohms = 12 ohms
The next step is to find It:
It = Et/Rt
It = 12 volts/ 12 ohms = 1 amp
Remember that:
It =I1=I2=I3...... !
Using Ohm's Law, each of the voltage drops can be found:
E1 = I1xR1
E1 = 1 amp x 1 ohm = 1 volt
(V1)
E2 = I2xR2
E2 = 1 amp x 9 ohms =
9 volts (V2)
E3 = I3 x R3
E3 = 1 amp x 2 ohms = 2 volts
(V3)
According to Kirchhoff's Voltage Law:
Et = E1+E2+E3....
12 volts = 1 volt + 9 volts + 2 volts
The first step is to find Rt:
Rt = R1+R2
Rt = 3 ohms + 1 ohm = 4 ohms
Then find It:
It = Et/Rt
It = 12 volts/ 4 ohms = 3 amps
Remember!! It =I1=I2=I3......
Then find the voltage drops:
E1 = I1 x R1
E1 = 3 amps x 3 ohms = 9 volts
(V2)
E2 = I2 x R2
E2 = 3 amps x 1 ohm = 3 volts
(V3)
There is no reading at V1 because there is no resistance - and therefore no voltage drop!
The voltage drops should equal the source voltage as a check:
Et = E1 + E2
Et = 9 volts + 3 volts = 12
volts
Problem #3
This is a tricky one! Notice there is MORE than one path for
current flow - therefore
this is no longer a SERIES circuit.
This is classified as a Complex Circuit (or combined
Series/Parallel circuit) - and a different
set of rules apply - so you must first learn the rules for
PARALLEL CIRCUITS! (Then you can come
back and attempt to solve this problem.)