Answer:
2. + 2.1
Explanation:
Formula for resistance is as follows
R_t = R₀ ( 1 + α t )
R_t is resistance at changed temperature , Ro is resistance at initial temperature , α is temperature coefficient of resistivity . t is temperature change .
For iron , R₀ = 10 , α = 5 x 10⁻³ , t = - 100 degree
R_t = 10( 1 + 5 x 10⁻³ x - 100 )
= 10( 1 - 5 x 10⁻³ x 100 )
10 x ( 1 - .5 )
10 x .5
For carbon
, R₀ = 10 , α = - 0.5 x 10⁻³ , t = - 100 degree
R_t = 10( 1 - 0. 5 x 10⁻³ x - 100 )
= 10( 1 + .5 x 10⁻³ x 100 )
10 x ( 1 + .05 )
10 x 1.05
Required ratio
= 10 x 1.05 / 10 x .5
= 105 / 50
= 21 / 10
= 2.1
