Question

what is the resultant resistance of two resistance 15 ohm and 10ohm connected in a series​

Answer 1

Explanation:

A resistance of 10 ohm is connected in series with two resistances each of 15 ohm arranged in parallel. What resistance must be shunted across this parallel combination so that the total current taken shall be 1.5A with 20V applied?

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Resistance seen from power supply is R1= 20/1.5=13.333 ohms

Substracting 10 ohms resistor in serie R1-10= 3.333 ohms=Rp or parallels resistance.

the two 15 ohms in parallel gaves half resistance 7.5 ohms

Rp=7.5*R / (7.5+R) or (7.5+R)*Rp=7.5*R solving for R

7.5 *Rp=R*(7.5-Rp) or R=7.5*Rp/(7.5-Rp) replacing Rp=10/3

R=75/(22.5-10)=75/12.5=6 ohms