Question

Three light sources A, B and C emit equal amount of radiant energy per unit time. The wavelengths emitted by the three source are 450 nm, 555 nm and 700 nm respectively. The brightness sensed by an eye for the sources are XA, XB and XC respectively. Then,
(a) XA > XB, XC > XB
(b) XA > XB, XB > XC
(c) XB > XA, XB > XC
(d) XB > XA, XC > XB

Answer 1

Three light sources A, B and C emit equal amount of radiant energy per unit time. The wavelengths emitted by the three source are 450 nm, 555 nm and 700 nm respectively. The brightness sensed by an eye for the sources are XA, XB and XC respectively. Then  XB > XA, XB > XC

Explanation:

Given in the question :

Three luminous sources A,B and C emit equivalent radiant energy per unit time. The wavelengths emitted by these three sources are 450 nm ,555 nm,and 700 nm.

Light Wavelength B is 555 nm. It has the greatest brightness; hence XB will be the lowest.  

Again 450 nm is closer than 700 nm to 555 nm.  

       $555- 450 = 105$

But  $700 - 555 = 145$

Therefore, the intensity of XA is greater than that of XC

Thus Option(c) is the correct answer