Board question (CBSE 2025 Main, 31/3/1 Q13): A wire of length ‘l’ is gradually stretched so that its length increases to 3l. If its original resistance is R, then its new resistance will be: (A) 3R (B) 6R (C) 9R (D) 27R
Full Electricity long video (every repeated question type, 2022–26):
A wire of length l is stretched to 3l. Its new resistance is not 3R: the volume stays the same, so the area also drops to A/3, and R = ρl/A becomes 9R. Solve it step by step.
Question (CBSE board question, verbatim): A wire of length ‘l’ is gradually stretched so that its length increases to 3l. If its original resistance is R, then its new resistance will be : (A) 3R (B) 6R (C) 9R (D) 27R
R₂ = ρ(3l) ÷ (A/3) = 3 × 3 × ρl/A = 9R, option (C).
Comment challenge: a 2 Ω wire is stretched to 4 times its length. Find the new resistance.
Quick recall (Electricity, Ohm’s law): 6 V across 3 Ω: current? I = V/R = 2 A.
Electricity quick revision (full video):
References: NCERT Class 10 Science, Ch 11 Electricity, §11.5 Factors on which the resistance of a conductor depends (R = ρl/A, resistivity ρ depends on the material) and §11.4 Ohm’s law (V = IR, so I = V/R); CBSE Class 10 board question and marking scheme ((C) 9R).
Narration uses a licensed AI voice (Azure AI Speech, Indian English). Script and physics research by ScoreSpark.
#class10 #cbse #electricity #resistivity #shorts
source
Board question (CBSE 2025 Main, 31/3/1 Q13): A wire of length ‘l’ is gradually stretched so that its length increases to 3l. If its original resistance is R, then its new resistance will be: (A) 3R (B) 6R (C) 9R (D) 27R
Full Electricity long video (every repeated question type, 2022–26): https://www.youtube.com/watch?v=MEab_ZNl5Lg
Answer: stretched to 4 times its length, the wire's area becomes A/4, so the new resistance = ρ(4l) ÷ (A/4) = 4 × 4 × ρl/A = 16 × 2 Ω, so R₂ = 32 Ω (not 8 Ω).
Quick recall (magnetic effects): Fleming's left-hand rule: first finger, second finger, thumb? → Field · current · motion (force)
Electricity quick revision (full video): https://www.youtube.com/watch?v=ppYotzJBczM