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JEE Main 2021 (1 Sep, Shift 2) · Combination of Resistors

Combination of Resistors question from JEE Main 2021 (1 Sep, Shift 2)

Q47JEE Main 2021 · 1 SEP · SHIFT 2Medium

Combination of Resistors

Two resistors R1 = (4 ±\pm 0.8) Ω\Omega and R2 = (4 ±\pm 0.4) Ω\Omega are connected in parallel. The equivalent resistance of their parallel combination will be:

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Answer: (c)

  1. Rp=R1R2R1+R2=168=2 ΩR_p = \dfrac{R_1 R_2}{R_1 + R_2} = \dfrac{16}{8} = 2\ \Omega.
  2. From 1Rp=1R1+1R2\dfrac{1}{R_p} = \dfrac{1}{R_1} + \dfrac{1}{R_2}: ΔRpRp2=ΔR1R12+ΔR2R22\dfrac{\Delta R_p}{R_p^2} = \dfrac{\Delta R_1}{R_1^2} + \dfrac{\Delta R_2}{R_2^2}
  3. ΔRp=4(0.816+0.416)=0.3 Ω\Delta R_p = 4\left(\dfrac{0.8}{16} + \dfrac{0.4}{16}\right) = 0.3\ \Omega
  4. So the answer is (c) (2±0.3) Ω(2 \pm 0.3)\ \Omega.
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