Given data: n=9.1×1028m−3 σ=6.4×107S∕m E=10N∕C e=1.6×10−19C m=9.1×10−31kg Step 1. Relation between conductivity and relaxation time (Drude model) σ=
ne2τ
m
⇒τ=
mσ
ne2
Step 2. Substitute values τ=
(9.1×10−31)(6.4×107)
(9.1×1028)(1.6×10−19)2
Compute step by step: Denominator: ne2=9.1×1028×(1.6×10−19)2 =9.1×1028×2.56×10−38 =2.33×10−9 Numerator: mσ=9.1×10−31×6.4×107=5.82×10−23 Now divide: τ=