Thermal Properties of Matter - Result Question 19

19. A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using [2013]

(a) Wien’s displacement law

(b) Kirchoff’s law

(c) Newton’s law of cooling

(d) Stefan’s law

Show Answer

Answer:

Correct Answer: 19. (a)

Solution:

  1. (a) Wein’s displacement law

According to this law

$ \lambda _{\max } \propto \frac{1}{T} $

or, $\lambda _{\text{max }} \times T=$ constant

So, as the temperature increases $\lambda$ decreases.