Advertisements
Advertisements
Question
The relative luminosity of wavelength 600 nm is 0.6. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm.
Advertisements
Solution
Given,
Relative luminosity = 0.6
Let P be the radiant flux of the source.
∴ Luminous flux = P × 685
Again, relative luminosity
`="Luminous flux of a source of given wavelength"/"Luminous flux of a source of 555nm of same power"`
`therefore0.6="Luminous flux of a source P watt"/(685P)`
`rArr685 xxPxx0.6=120xx685`
`rArr P=120/0.6=200W`
So, 200 W radiant flux is needed to produce the same brightness sensation for 600 nm wavelength.
APPEARS IN
RELATED QUESTIONS
What is the luminous flux of a source emitting radio waves?
The luminous flux of a 1 W sodium vapour lamp is more than that of a 10 kW source of ultraviolet radiation. Comment.
As the wavelength is increased from violet to red, the luminosity ____________ .
An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about ___________ .
Light from a point source falls on a screen. If the separation between the source and the screen is increased by 1%, the illuminance will decrease (nearly) by ____________ .
The intensity produced by a long cylindrical light source at a small distance r from the source is proportional to _________ .
A photographic plate placed a distance of 5 cm from a weak point source is exposed for 3 s. If the plate is kept at a distance of 10 cm from the source, the time needed for the same exposure is _____________ .
A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance r from the source as ___________ .
The brightness-producing capacity of a source
(a) does not depend on its power
(b) does not depend on the wavelength emitted
(c) depends on its power
(d) depends on the wavelength emitted
A source emits 45 joules of energy in 15 s. What is the radiant flux of the source?
A photographic plate records sufficiently intense lines when it is exposed for 12 s to a source of 10 W. How long should it be exposed to a 12 W source radiating the light of same colour to get equally intense lines?
Two light sources of intensities 8 cd and 12 cd are placed on the same side of a photometer screen at a distance of 40 cm from it. Where should a 80 cd source be placed to balance the illuminance?
Light rays from a point object ______.
