Rankers Physics
Topic: Current Electricity
Subtopic: Relation between Current and Drift Velocity

The resultant resistance value of n resistance each of r ohm when connected in parallel, is x. When these n resistances are connected in series, the resultant value is :  
nx
n²x
rnx
r²x/n

Solution:

Let's break this down step by step.

1. Resistances connected in parallel

When

nn

resistors, each of resistance

rr

, are connected in parallel, the total or equivalent resistance

RparallelR_{\text{parallel}}

is given by the formula:

 

1Rparallel=1r+1r++1r(n terms)\frac{1}{R_{\text{parallel}}} = \frac{1}{r} + \frac{1}{r} + \cdots + \frac{1}{r} \quad \text{(n terms)}

 

This simplifies to:

 

1Rparallel=nr\frac{1}{R_{\text{parallel}}} = \frac{n}{r}

 

So, the equivalent resistance is:

 

Rparallel=rnR_{\text{parallel}} = \frac{r}{n}

 

We're told that the resultant resistance when connected in parallel is

xx

, so:

 

x=rnx = \frac{r}{n}

 

2. Resistances connected in series

When the same

nn

resistors, each of resistance

rr

, are connected in series, the total or equivalent resistance

RseriesR_{\text{series}}

is simply the sum of the individual resistances:

 

Rseries=r+r++r(n terms)R_{\text{series}} = r + r + \cdots + r \quad \text{(n terms)}

 

So:

 

Rseries=n×rR_{\text{series}} = n \times r

 

3. Relating the two scenarios

From the parallel connection, we know that:

 

x=rnx = \frac{r}{n}

 

Thus, the resistance when the resistors are connected in series is:

 

Rseries=n×r=n×(x×n)=r×n×xR_{\text{series}} = n \times r = n \times \left( x \times n \right) = r \times n \times x

 

Therefore, the resistance when these

nn

resistors are connected in series is:

 

r×n×x\boxed{r \times n \times x}

 

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