Question

2. Given three resistances of 30 ohm each. How can they
be connected to give a total resistance of (1) 90 ohm
(in) 10 ohm (iii) 45 ohm ?
(Ans (1) in series (ii) in parallel (iii) two
resistances in parallel and one in series)​

Answer 1

Explanation:

in this way we can connect the resistors to get the desired resultant resistance..

Answer 2

Given,

All the three resistances are equal.

R1=R2=R3=30 ohm.

Solution:

(1)The resistors will be connected in series to give the total resistance as 90 ohm.

When the resistors are connected in series, the net resistance is calculated as:

Rnet=R1+R2+R3

When there are n resistances of equal value connected in series,

Rnet=nR.

90 ohm=3x30 ohm.

Thus they should be connected in series.

(2)The resistors will be connected in parallel to give the total resistance as 10 ohm.

When there are n resistances of equal value connected in parallel,

Rnet=R/n

10 ohm=30/3 ohm.

Thus they should be connected in parallel.

(3The two resistors will be connected in parallel and the third in series.

Rp-resistors connected in parallel

Rs-resistor in series

Rp=30/2 ohm

Rp=15 ohm.

Rs=30 ohm.

Rnet=Rs+Rp

Rnet=(15+30) ohm

Rnet=45 ohm.

Two resistors in parallel and the third in series will give the net resistance as 45 m.

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