Question

A students records the initial length l, change in temperature ∆T and change in length ∆l of a rod as follows :

If the first observation is correct, what can you say about observation 2, 3 and 4?

Answer 1

\(\alpha=\frac{ΔI}{IΔT}\)

From I observation,

\(\alpha=\frac{4\times10^{-4}}{2\times10}\)

\(=2\times10^{-5}C^{-1}\)

For II, observation   Δl=\(\alpha/ΔT \)

= 2 × 10^-5 × 1 × 1 

= 2 × 10^-4 ≠ 4 × 10^-4 m

For III, observation    

Δl=\(\alpha/ΔT \)

= 2 × 10^-5 × 2 × 20 

= 8 × 10^-4 m 

= 2 × 10^-4 m

For IV, observation  

 Δl=\(\alpha/ΔT \)

= 2 × 10^-5 × 3 × 10 

= 6 × 10^-4 m = 6 × 10^-4 m 

Therefore, IV observation is correct and II, III are wrong