CBSE 2026 · Region 5 · Set 1 · Q38

Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire. Shweta put nichrome wire of length ' $\displaystyle l$ ' in the circuit and after plugging the key, noted current in the ammeter. Ayesha put nichrome wire of same thickness but twice the length i.e. ' $\displaystyle 2 l$ ' in the circuit and after plugging the key, noted current in the ammeter. Samridhi took copper wire of length ' $\displaystyle l$ ' and same thickness in the circuit and after plugging the key, noted current in the ammeter.

(a)

If the ammeter reading is X ampere with nichrome wire of length ' $\displaystyle l$ ', then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?

(b)

What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ' $\displaystyle l$ ' the same ?

(c)OR(c)

Define 'resistivity'. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.