Question

When an iron rod is heated in a furnace, the colour of the iron rod first turns dull red and on further increase in temperature it changes to bright red to orange, then yellow, progressively white and then finally blue at the elevated temperatures.
This sequence of colours observed on heating an iron rod are in the sequence of __________

• A. Increasing wavelength
• B. Decreasing wavelength
• C. Decreasing frequency
• D. None of the above

Answer 1

The correct option is B Decreasing wavelength

When an iron rod is heated its colour changes to blue from red. Red light has higher wavelength and blue light has lower wavelength which means that the radiation emitted goes from a higher wavelength to lower wavelength.
Since wavelength is inversely proportional to the temperature of the body, higher the temperature, lower will be the wavelength.