Electronics - Series-Parallel Circuits - Discussion

8. 

With 21 V applied, if R1 = 5 ohms, R2 = 35 ohms, and R3 = 14 ohms, what is the current of R2 if R1 is series connected with parallel circuit R2 and R3?

[A]. 200 mA
[B]. 800 mA
[C]. 600 mA
[D]. 400 mA

Answer: Option D

Explanation:

No answer description available for this question.

Maddy said: (Apr 18, 2011)  
May be the answer is 600ohm
Plz check someone and explain if answer is 400ohm.

Swastik said: (Jun 3, 2011)  
R2 & R3 are in parallel and then in series with R1
Solving, Eq Resistance = 15ohm
Then V(given)=21 V
So I=V/R=21/15 = 1.4Amp

Current across R2(By Current Divider Rule Formula)
= 1.4 x 14(R3)/(35+14)= 0.4Amp = 400 mA

Orange said: (May 23, 2014)  
By applying mesh analysis at each loop.

40I1-35I2=21---->eqn(1).
-35I1+49I2=0----->eqn(2).

RESOLVING BOTH WE GET,

I1=1.1amp and I2= 1.5amp.
current at R2 is I1-I2 =====> 1.5-1.1=0.44amp=400mA.

James Adams said: (Apr 23, 2015)  
Where did the 15 ohms come from?

Jhedd said: (Aug 10, 2015)  
It is the total resistance.

Pankaj said: (Aug 12, 2015)  
1st calculate the total Resistance.

Rt = R1+R2||R3.

= 5+(35*14)/35+14 = 15.

According to voltage divider:

Voltage across R1 is V1 = v*R1/Rt.

V1=21*5/15=7.

Then voltage across the parallel circuit is 21-7=14;

Then current across I2 = 14/R2 = 14/35 = 0.4 A or 400 mA.

Chinmay said: (Feb 20, 2016)  
I satisfied with your explanation.

Deepthi said: (Aug 31, 2016)  
Thanks @Pankaj.

Happy said: (Sep 15, 2016)  
Thanks, @Pankaj. Your explanation is very nice.

P@$Hoo said: (Oct 19, 2016)  
Nice explanation @Pankaj.

Kamran said: (Oct 27, 2016)  
Thanks @Pankaj.

Lester said: (Dec 17, 2016)  
Not getting, please explain the solution.

Tayyab Rehaman said: (Mar 25, 2017)  
Good explanation, Thanks @Pankaj.

Manish said: (Apr 13, 2017)  
If a series"parallel circuit has all 30-ohm resistors, what is the total resistance when R1 is in series with a parallel circuit consisting of R2 and R3?

* 45
* 50
* 60
* 90

Please give me the answer.

Damchi said: (May 23, 2017)  
Loop1: V =i1(R1+R2) - i2R2.
=> 21=40i1-35i2 ---------1.

Loop2: - i1R1+i2(R2+R3) =0.
=> - 35i1+49i2=0.
=> i1=(49/35)i2=(7/5)i2-------2.

Solving 1 and 2,
i2 = 1 A
i1 = 1.4 A.

Current through R2 = i1-i2
= 0.4 A = 400 mA.

Vishal said: (Aug 31, 2018)  
Nice explanation @Pankaj.

Gurcharn said: (Feb 1, 2019)  
I think 600 mA.

Red said: (Mar 17, 2020)  
In a circuit, R1 and R2 are connected in series having a resistance of 5 ohms and 10 ohms respectively. The voltage across resistor R1 is equal to 4 V. Find the current passing through R2 and the voltage across the same resistor.

Please help.

Red said: (Mar 17, 2020)  
A parallel circuit has three branches of 6 ohms, 12 ohms, and 20 ohms. If A of current flows through the 12-ohm branch, what is the current flow through the 20-ohm branch?

Red said: (Mar 17, 2020)  
A lamp rated at 120 V, 100 W is to be used on a 220 V line. What size of the resistor should be connected in series with the lamp for correct operation?

Red said: (Mar 17, 2020)  
A store lightning system consists of 25 lamps of 100 watts each connected in parallel with 120 V sources. What is the total resistance of this system?

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