Explain why : an optical pyrometer (for measuring high temperatur… - Vidyadip

Question

Explain why :
an optical pyrometer (for measuring high temperature) calibrated for an ideal black-body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct
value for the temperature when the same piece is in the furnace.

✓

Answer

Keeping the red hot iron piece in the open the emitted radiation energy $E=\sigma\left(T^4-T_0^4\right)$.
Where $T _{ o }$ is the temperature of the environment. So the measured temperature will be less but when this piece is in the furnace it will be $E =\sigma T ^4$. So the measured temperature will give correct value.

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