MCQ
Three light sources $A, B$ and $C$ emit equal amount of radiant energy per unit time. The wavelengths emitted by the three sources are $450\ nm, 555\ nm$ and $700\ nm$ respectively. The brightness sensed by an eye for thesources are $X_{A,} X_B$ and $X_C$ respectively. Then,
  • A
    $X_A > X_B, X_C > X_B$
  • $X_A > X_B, X_B > X_C$
  • C
    $X_B > X_A, X_B > X_C$
  • D
    $X_B > X_A, X_C > X_B$

Answer

Correct option: B.
$X_A > X_B, X_B > X_C$
Wavelength of light $B$ is $555\ nm.$ It has the highest luminosity$;$
hence$, X_B$ will be highest.
Again, $450\ nm$ is nearer to $555\ nm$ than $700\ nm.$
$\therefore 555 - 450 = 105$
But $700 - 555 = 145$
So$, X_A\ 's$ brightness will be greater than that of $X_C.$

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