Can inserting a resistor in a circuit produce an effect similar to a short circuits?

Question

circuits subject

Answer 1

Yes.

A low value resistor wired between two points in a circuit will produce the same effect as a short between those two points.

low value means 1 ohm. Some cases 10 ohms or even 100 ohms will have the same effect.

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Answer 2

Short Answer: Yes, inserting a resistor into a circuit CAN produce a symptom similar short circuit.

1. The resistor must be  placed in parallel with other resistors in the circuit.

2. The resistor must have the smallest resistance compared to the other resistors in the parallel group.

Long Answer: Yes, because ......

Say you have a simple 120VAC circuit going though a fuse, a fixed resistor, and a light bulb.  All components are wired in series.

120VAC HOT--->F1---->R1--->R2--->Neutral

The fuse F1 is rated for 5 amp

The resistor R1 has a resistance of 35 ohms

The light bulb R2 is rated 5 ohms.

Assuming the wire has negligible or 0 impedance: Ohm's Law says E=IR (Voltage=Current*Resistance)

plugging in from the example,

E=120

R = 40 (R1 + R2).

We solve for current which is I

120=I(40)

120/40=I

3=I

Current = 3 amps

Because the fuse is rated for 5 amps, the circuit is protected up to 5 amps. If the current gets any higher it will blow the fuse.

Now look what happens if we place a 10 ohms resistor (R3) in parallel with the 35 ohms resistor from the original circuit.



120VAC HOT--->F1--->(parallel R1+ R3)--->R2--->Neutral

                                          

When resistors in placed are parallel the total resistance is the inverse of all the inverted resistance values combined. From our example, the 10 resistor is in parallel with the 35 ohm resistor so the resistance of that section of the circuit is:

RT=1/(1/R1 + 1/R3)= 1(1/10 +1/35) = 1/(0.1 + 0.029) = 1/0.129=7.75 ohm.

Here’s how it works out

E=120

R= 12.75 (RT + R2 )

Again we solve for current which is I

120=I(12.75)

120/12.75=I

9.4=I

Current = 9.4 amps

With 9.4 amps flowing through the circuit, the fuse will blow acting like there is a short in the circuit.

Answer 3

It should do the opposite.  It resists current so there is a voltage drop across the resistor.

How many ohms is the resistor and what's the voltge?