A metallic wire has variable cross sectional area. Cross sectional area at cd is twice the area at ab. The wire is connected to a cell as shown. Find the ratio of heat dissipated per unit volume at section cd to that at section ab.

Question

G1 Physics · Accepted Answer

Image The same current flows through every cross-section. Joule heating per unit volume is p = J²ρ = (I/A)²ρ. Since A(cd) = 2A(ab), p(cd)/p(ab) = (A(ab)/A(cd))² = 1/4.