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Two identical conducting slabs, each of resistance R, are joined end to end so the total length doubles while the cross-sectional area is unchanged. The resistance of the combination is
AR/2
BR
C2R
D4R
Answer & Solution
Correct answer: C. 2R
1. Resistance is proportional to length: $R \propto l$.
2. Doubling the length (area fixed) doubles the resistance.
3. The combination acts like one slab of length $2l$, so $R_c = 2R$.
4. R/2 would apply if area doubled; 4R has no basis here.
_Source: NCERT Class 12 Physics Ch 3 "Current Electricity", p.3_
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