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MCQ practice · SSC Physics Board questions · Chapter 11: Current Electricity

Chattogram Board 2021

Which of the following relations is correct?

Think it through first, then pick an option.

  1. a V = R/I
  2. b R = ρA/L
  3. c ρ = R·A/L
  4. d A = Rρ/L
Answer and explanation

Correct answer: c ρ = R·A/L

From R = ρL/A we get ρ = RA/L.

Why the other options are wrong

  • a V = R/I: V = R/I is upside down; by Ohm's law V = I × R.
  • b R = ρA/L: R = ρA/L is not right; the correct form is R = ρL/A, since R ∝ L and R ∝ 1/A.
  • d A = Rρ/L: A = Rρ/L is not right; from R = ρL/A we get A = ρL/R.