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1% of light of a source with luminous in...

1% of light of a source with luminous intensity 50 candela is incident on a circular surface of radius 10 cm . The average illuminance of surface is

A

100 lux

B

200 lux

C

300 lux

D

400 lux

Text Solution

Verified by Experts

The correct Answer is:
b
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Photometry: The measurement of light as perceived by human eye is called photometry. Photometry is measurement of a physiological phenomenon, being the stimulus of light as received by the human eye, transmitted by the optic nerves and analysed by the brain. The main physical quantities in photometry are (i) the luminous intensity of the source, (ii) the luminous flux or flow of light from the source and (iii) illuminance of the surface. The SI unit of luminous intensity (I) is candela (cd). The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 xx 10^12 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian. If a light source emits one candela of luminous intensity into a solid angle of one steradian, the total luminous flux emitted solid angle is one lumen (1m). A standa o incandescent light bulb emits approximately 1700 lumens. The SI unit of luminous intensity is:

ERRORLESS -RAY OPTICS-Photometry
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  15. An electric lamp is fixed at the ceiling of a circular tunnel as shown...

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  16. When sunlight falls normally on earth, a luminous flux of 1.57 xx 10^(...

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  17. In the above problem, the luminous flux emitted by sun will be

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  18. A screen receives 3 watt of radiant flux of wavelength 6000 Å . One lu...

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  19. A point source of 3000 lumen is located at the centre of a cube of sid...

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  20. A point source of light moves in a straight line parallel to a plane t...

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