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
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Answer:
Correct Answer: 19. (a)
Solution:
- (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.
