Question

A student has two resistors- 2 Ω and 3 Ω. She has to put one of them in place
of R2 as shown in the circuit. The current that she needs in the entire circuit is
exactly 9A. Show by calculation which of the two resistors she should choose.​

Answer 1

Answer:

2 Ω

Explanation:

The overall current needed = 9A. The voltage is 12V  

Hence by Ohm’s Law V=IR,  

The resistance for the entire circuit = 12/9 = 4/3Ω = R  

R1 and R2 are in parallel.  

Hence, R=(R1R2) / (R1+R2) = 4R2 / (4+R2) = 4/3  R2 = 2Ω

Answer 2

Students has to put 2 ohm Resistor in place of R2

Explanation:

Battery Source = 12 V

=> V = 12 V

Total Current = 9 A

Total Resistance = R

V = IR

=> 12 = 9R

=> 4 = 3R

=> R = 4/3

R1 & R2 are in Parallel

Hence

1/R = 1/R1 + 1/R2

=> 1/(4/3) = 1/4 + 1/R2

=> 3/4 = 1/4 + 1/R2

=> 2/4 = 1/R2

=> 1/2 = 1/R2

=> R2 = 2

Students has to put 2 ohm Resistor in place of R2