The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency '$$A$$' $$\times 10^{12}$$ hertz and that has a radiant intensity in that direction of $$\frac{1}{B'}$$ watt per steradian. '$$A$$' and '$$B$$' are respectively

This question tests knowledge of the SI definition of the candela, the base unit of luminous intensity.

The Official SI Definition of the Candela:

The candela is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency $$540 \times 10^{12}$$ hertz and that has a radiant intensity in that direction of $$\frac{1}{683}$$ watt per steradian.

Why these specific values?

- The frequency $$540 \times 10^{12}$$ Hz corresponds to green light with a wavelength of approximately 555 nm. This is chosen because the human eye is most sensitive to light at this wavelength (the peak of the photopic luminosity function).

- The factor $$\frac{1}{683}$$ W/sr is chosen to maintain consistency with the historical definition of the candela, ensuring backward compatibility with previous measurement standards.

Matching with the question format:

The question states the frequency is $$A \times 10^{12}$$ Hz, so $$A = 540$$.

The question states the radiant intensity is $$\frac{1}{B}$$ W/sr, so $$B = 683$$.

The correct answer is Option 1: 540 and 683.