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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

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Answer:

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The current she needs in the entire circuit is 9 A. 

Therefore, we choose case 1.

So, R 2 = 2 ohm

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Transcript

Question 4 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 Case 1 : She uses the 2 ohm resistor. So, R2 = 2 ohm R1 = 4 ohm R1 & R2 are connected in parallelCase 2 : She uses the 3 ohm resistor. So, R2 = 3 ohm R1 = 4 ohm R1 & R2 are connected in parallel Let total resistance be R 1/𝑅=1/𝑅1+1/𝑅2 1/𝑅1=1/4+1/2 1/𝑅1=(1 + 2)/4=3/4 Therefore, R = 4/3 Given, V = 12 volts According to omh’s law V = 𝐼/𝑅 So, I = 𝑉/𝑅Let total resistance be R 1/𝑅=1/𝑅1+1/𝑅2 1/𝑅1=1/4+1/3 1/𝑅1=(3 + 4)/12=7/12 Therefore, R = 12/7 Given, V = 12 volts According to omh’s law V = 𝐼/𝑅 So, I = 𝑉/𝑅= 12/((4/3) ) = ((12 × 3))/4 = 9 A= 12/((12/7) ) = ((12 × 7))/12 = 12 A The current she needs in the entire circuit is 9 A. Therefore, we choose case 1. So, R2 = 2 ohm

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo