Electronics - Parallel Circuits - Discussion

One way to start is that, the power comes from the smallest resistor. So, after verifying that currents through R3 and R2(0.04A) and R4(0.012) sum up to 0.052A, we search for a smaller value for R1 that could elevate the power to 9.408W which is exactly 1/3K.

How the current flows, when the source is open circuited with voltmeter.

I1=V/R=48/1K=48mA=0.048A
It=I1+0.052(in circuit itself)
It=0.048+0.052=0.1A
It=0.1A

P=VI
P=48*0.1=4.8W

so the watt meter reading should be 4.8 watts but the circuit shows 9.408W.

so mistake in R1.

Answer is A

P = VxIt
It = P/V = 9.408/48 = 0.196A (Total Current)

IR4 = 0.012 A (Given)

R4 = 48/0.012 = 4000 = 4K R4 is correct

IR3 = V/R3 = 48/3000 = 0.016A
IR2 = V/R2 = 48/2000 = 0.024A
IR1 = V/R1 = 48/1000 = 0.048A

IR3 = (I3-I4)
I3 = (IR3+I4)
I3 = (0.016+0.012)=0.028A

R3 = V/(I3-I4) = 48/(0.028-0.012) = 3000 = 3K R3 is correct

R2 = V/(I2-I3) = 48/(0.052-0.028) = 2000 = 2K R2 is also correct

R1 = V/(It-I2) = 48/(0.196-0.052) = 333.33ohms which is notcorrect

since R1=1000ohms = 1k from the given circuit

@ vinoth: that's a wattmeter..not a voltmeter...

@ H@R you are correct!

Circuit itself wrong. voltmeter is connected in series with circuit no current flows.

P = V*I .... I = P/V = 9.408/48 = 0.196A (Total Current)
Current on R1 = 0.196 - 0.052 = 0.144A
R1 = 48V/0.144A = 333.33 Ohm (Should be the correct value of R1)

Given total power=9.408
Power of r1=48/1*1000=.48mW
r2=48/2*1000=.24mW
r3=48/3*1000=.16mW
r4=48/4*1000=.12mW

Total power = 1W
But the total power given=9.408W.
ie, one resistor is wrong value.
................................................................

0.012A is current through R4
I R4= 48/4*1000 = .012A

So R4 is correct value
.................................................................

0.053 is the current total through r2, r3 and r4 as branch current total.
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We know that current through R4=.012

I (R2+R3) = V/(R2*R3/R2+R3)

=48/(2*3/2+3)1000
=48/(6/5)1000
=48/1200
=.04

Then I(R2+R3+R4)= .04+.012 = .052

So that R2,R3,R4 are correct.

i.e. R1 is wrong

Can any one give the correct explanation?