Discussion :: Parallel Circuits  General Questions (Q.No.25)
25.  Which component is open? 

Answer: Option C Explanation: No answer description available for this question.

Sasi said: (Jan 10, 2011)  
If R3 get open means R4 also opened. So, we can get a maximum output. 
Krishnan said: (May 22, 2011)  
I don't understand its meaning. 
Deepti said: (Jun 22, 2011)  
Total current = 21mA Current through R1 & R2 = 18mA So it needs R1 & r2 equivalent = 2/3 which is true. So R1 R2 not open Now total voltage acrros last branch = 12v which is given by R4 ( 4Kohm * 3mA)so there is no need of R3 Hence it is opened. 
Gopiram Verma said: (Jul 31, 2011)  
Good explanation deepti. 
Hanish said: (Dec 7, 2011)  
Super deepi. 
Sreeyush Sudhakaran said: (Feb 20, 2012)  
It=I1=0.021A I3=0.003A IR1=12/1K=0.012A IR2=12/2K=0.006A IR3=12/3K=0.004A IR4=12/4K=0.003A here we can see that IR4=I3 (0.003A) ie no current is flowing through R3 Also It=IR1+R2+IR3+IR4=0.012+0.006+0.004+0.003=0.025 Which is not correct. By open circuiting R3 we get It=0.012+0.006+0.003=0.021 which is correct. So R1 is open in the circuit 
Kishu said: (Jun 4, 2012)  
Answer R1 is open because current not flow in R1 because there is short circuit across R1 current always flow in low resistive path. 
Saurabh said: (Jul 18, 2012)  
This is not clear how R3 is open connection means only one pole is connected. 
Subedar Sk Shakya said: (Jan 30, 2013)  
As we know in parallel circuits current divides& voltage remains same here the first amp meter shows 0.021A is the total current flowing through the R1,R2,R3,R4 and second one shows the current flowing through R3&R4 Now current reading for first one r1*r2/r1+r2=1*2/1+2 =2/3 I=V/R so(12)/(2/3)= 18ma now remains 3ma for second one so it clearly shows again I= V/R =12/4k=3ma So no need of R3. Here R3 is Open. 
Jaganadhan.R said: (Jun 7, 2013)  
Hi, Total current = 21mA. Current required by R1 and R2 = 18mA. So for remaining 3mA(21mA 18mA), R4 = 4K is enough no need for R3. Thank you. 
Aneel said: (Jun 9, 2013)  
How to calculate total current? 
Suresh B said: (Jul 14, 2014)  
1 amp = 1000 mA. 0.021 A = 21 mA. 
Priya said: (Dec 15, 2014)  
@Kishu is right. We can't connect volt and ammeters directly because their will be short circuit. 
Hima.V.M said: (Nov 15, 2016)  
It's a clear explanation, Thank you @Deepti. 
Naveen said: (Jun 27, 2017)  
Perfect explanation, Thanks. 
Mani said: (May 1, 2018)  
Here we have a total current of the 21m amp, Current across R1is. I1=v/R1=12/1*10^3=12m amp Current across R2 is; I2=v/R2=12/2*10^3=6m amp, Remaining current is 3m amp. Then current across R4 is, I3=v/R4=12/2*10^3=3m amp, Hence resistor R3 is open circuit. 
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