How can you solve this circuit? I've tried, but I'm stuck. I don't know how to work backwards on this.
http://img441.imageshack.us/img441/8/circuitii7.jpg
Thanks for any help you can give me!
2007-06-16 02:45:57 · 4 answers · asked by F E 2 in Science & Mathematics ➔ Engineering
use kirchoffs law..
i cannot explain this to u ...
i have to do thi physically..
u will be unable to understand...
i can give u idea...k
use kirchoffs law.......
firat move from higher to lower potential in the circui which u know(u dont move in that arm off the circuit where u dont know the resistance...)
and then u move in that circuit where u do not,.know the resistance.....
solve the 2 equation u'll get...it
,...
OR
still wonderinf whats this...
go to basics...
ohms law....
You have to find the total R for the resistors in parallel:
1/Rt=1/R2+1/R3
=> Rt=(R3R2)/(R3+R2)
=> 2R3/2+R3=2R3
Apply the equation V=IR
=> 20=(2.5)(Rt+R1)
=> 8=Rt+4 => Rt=4
Rt=2R3
=> R3=2
is the answer...
all the best...
2007-06-16 02:51:21 · answer #1 · answered by Rohan 4 · 0⤊ 0⤋
The voltage across R2 = I 2 x R2 = 2 ohms X 2.5 Amps
= 5 Volts
The voltage across R3 also will be the same as they are parallel. Out of total 20 volts, the remaining 15 volts will be across the 4Ohm resistor as this resistor and the parallel combination of R2 and R3. are in series.
The current through the 4 ohm resistor is = V/R = 15/4 Amps
=3.75 Amps
This is the sum of the currents through R2 and R3
There for the current through R3 = 3.75 Amps - 2.5 Amps
ie.: = 1.25 Amps
The voltage across R3 is 5Volts
Hence, R3 = 5 Volts/1.25 Amps = 4 Ohms....Ans
2007-06-16 10:07:53 · answer #2 · answered by Joymash 6 · 2⤊ 0⤋
Well, since you know the current through R2 and it's value, you can now calculate the voltage across R2.
Using that voltage calculate the series equivalent resistance of R2 and R3 in parallel to get that voltage formed by the divider or R1 and the combination of R2/R3. Use that resistance to calculate the value of R 1 neded to generate that parallel combination vaue.
There are other ways to do it also, by the way.
2007-06-16 09:56:20 · answer #3 · answered by Gene 7 · 0⤊ 0⤋
1) You have to find the total R for the resistors in parallel:
1/Rt=1/R2+1/R3 => Rt=(R3R2)/(R3+R2)=2R3/2+R3=2R3
2) Apply the equation V=IR => 20=(2.5)(Rt+R1) =>
8=Rt+4 => Rt=4
3) Rt=2R3 => R3=2
2007-06-16 09:56:20 · answer #4 · answered by Anonymous · 0⤊ 0⤋