Question

Three light source A, B and C emit equal amount of radiant energy per unit time. the wavelength emitted by the three source are 450 nm, 555 nm and 700 nm respectively. The brightness sensed by an eye for the source are $X_A,X_{B}and{X}_C$ respectively. then,

• A. $X_A>X_B,X_C>X_B$
• 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 1

The correct option is C $X_B>X_A,X_B>X_C$

With increase in wavelength of visible light, the sensitivity to eye increases, reaches a peak at 555 nm and then decreases.

So brightness sensed is maximum for 555 nm with brightness sensed being less than it for both 450 nm and 700 nm.

$X_B>X_A,X_B>X_C$