Electronics - Parallel Circuits - Discussion


What happens to total resistance in a circuit with parallel resistors if one of them opens?

[A]. It increases.
[B]. It halves.
[C]. It remains the same.
[D]. It decreases.

Answer: Option A


No answer description available for this question.

Raji said: (Dec 24, 2010)  
We know that if voltage increases, current increases & if resistor increase then current decreases.. then in parallel current ckt as increases total resistance also increases...

S.Jeyasudha said: (Jun 13, 2011)  
According to the parallel resistance circuit the equivalent resistance is given by RT=R1||R2= (R1*R2)/(R2+R2. That answer will be less compare with when any one resistance open, because the total resistance is equalto RT=R1 or R2 only. So RT is increases.

Aditya said: (Jul 13, 2011)  
If we consider the two resistance in parallel, r1 &r2, So according law R1*R2/ (R1+R2). If one of them is open means R1=NO, So it will be R2 in Series. So total resistance will decrease.

Ankit said: (Aug 1, 2011)  
As we know for a particular resistor in series net resistance is greater than a resistance in parallel if we remove resistor of one of them from a parallel circuit the net result will increases as reverse as in series.

Nandini said: (Oct 30, 2011)  
Can you give me the proper explanation? I want correct answer.

Ragi G R said: (Jan 11, 2012)  
In parallel resistance the effective resistance value will be less than the smallest valued resistance. For eg, if a 2 ohm and 3 ohm resistance are in parallel effective resistance will be less than 2 ohm. So when one is opened the effective resistance increases.

Sreeyush Sudhakaran said: (Feb 19, 2012)  
Case 1: R1&R2 in parallel


Case 2 : R2 is open circuited

RT= R1

To understand correctly

case 1: R1=1k R2=1k

RT= (1x10^6)/(2x10^3)

RT= 0.5k

case 2: R1=1k


So RT increases with removal of R2

Matthew said: (May 4, 2012)  
Consider two resistors in parallel. Their total resistance is,

(R1 * R2) / (R1 + R2)

We would like to determine the effect of opening R2. The circuit then contains a single resistor, R1 in series. We would then like to determine whether ? is > or < in the below equation,

(R1 * R2) / (R1 + R2) ? R1

Let's multiply both sides of this inequality by (R1 + R2), which yields,

R1 * R2 ? R1 * (R1 + R2)

expanding the right hand side yields,

R1 * R2 ? R1^2 + R1 * R2

Since resistance is always positive, we have that the right hand side is larger. Therefore, we conclude that resistance will increase.

Prasanna said: (Aug 19, 2012)  
Let me explain with the example

R1 = 4 & R2 =4
RT = R1* R2/( R1+R2)
=2 ohms

If R1 is open then R1= not available
So RT = R2

That means total resistance increases as one of the resistance is opened.

Subrata said: (Feb 20, 2013)  
What will be answered if more than two resistance is connected in a circuit? Like, r1=2, r2=3, r3=4.

Sushil said: (May 3, 2013)  
In series voltage is constant therefore in the circuit only changes current ane of the fact is that resistance decreases then current also increases as per ohms law.

Roshan said: (Oct 11, 2013)  
As circuit is open no current flows & infinite resistance.

Bhargavi Veera said: (Nov 30, 2013)  
Same question in series then then total resistance what happen?

Abc said: (Feb 5, 2014)  
If one of the resistors that are connected in series is opened, then total resistance becomes infinite.

Spurthi said: (Oct 4, 2014)  
If any one of the resistor connected in parallel is open can we take that resistor value as 0?

Ravi said: (Dec 19, 2014)  
Take V = IR relation.

In parallel circuit voltage is constant. So IR must be a constant value if one terminal is open means I = 0. So R became infinity.

Keerthi Raj said: (Feb 3, 2015)  
Suppose if you have more than 2 resistors say r1=r2=r3=2 ohm then the equivalent resistance is around 1.3 ohm.

Say r3 is opened then the equivalent resistance is 1 ohm hence from this the resistance is decreased. If we consider only 2 resistors in parallel then the resistance will be increased.

Azhagusurya said: (Feb 20, 2015)  
Consider r1 ,r2 are the resistance which are in parallel.

If any one of resistor get open mean the connection became series.


r1 = 2kohm.
r2 = 1kohm.

If both are in parallel means Rt = r1*r2/(r1+r2) = 2/3 = 0.667 kohm.

If both are in series means,

Rt = r1+r2.
Rt = 2+1 = 3kohm.

So resistance value increases when one of them get opened.

Vicky Meena said: (Mar 10, 2015)  
How many resistor is there?

Vicky said: (Oct 11, 2015)  
What happens to total resistance in a circuit with parallel resistors if one of them opens?

Anyone explain this question please?

Mithun said: (Oct 13, 2015)  
No. The given answer is wrong. It may increase or decrease resistance value depending on the value of resistance.

Sooraj said: (Aug 9, 2016)  
If R1 is in series with parallel connected to R2 and R3, what happens to total current if R2 opens?

Shandelin Priyanka said: (Jun 11, 2017)  
Three identical resistors are connected in series to a battery. If the current of 12 A flows the battery, how much current flows through any one of the resistors?

Can anyone answer this?

Tushar said: (Jun 15, 2019)  
If one of the resistors in a parallel circuit, is removed, what happens to the total resistance?

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