The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency ‘A’ × 10¹² hertz and that has a radiant intensity in that direction of 1/B watt per steradian. ‘A’ and ‘B’ are respectively:

Candela Definition Based Question | JEE Main PYQ | Structure of Atom

Q. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency ‘A’ × 10¹² hertz and that has a radiant intensity in that direction of 1/B watt per steradian. ‘A’ and ‘B’ are respectively

(A) 450 and 683

(B) 540 and 1/683

(D) 450 and 1/683

Correct Answer: (C) 540 and 683

Explanation

By SI definition, one candela is the luminous intensity of a source emitting monochromatic radiation of frequency 540 × 10¹² Hz and having a radiant intensity of 1/683 watt per steradian in that direction.

Hence,
A = 540
B = 683

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