Parallel Resistance of Composite Strip

Correct Answer

B — 4/3 Ω

Concept and Reasoning

The added metal has twice copper resistivity and the same length and cross-sectional area, so its resistance is 4 Ω while the copper strip is 2 Ω. Because both layers experience the same end-to-end voltage, they conduct in parallel, giving 2||4=4/3 Ω.

Calculation / Key Relation

Rmetal=2Rcopper=4Ω

Req=(2×4)/(2+4)=4/3Ω

Exam Takeaway

Bonded layers along the same length act as parallel conducting paths.

Common Mistake

Do not add the two layer resistances in series.