Photometry Physics - Photometry

What is the luminous flux of a source emitting radio waves?

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:

1. 0.5%
2. 1%
3. 2%
4. 4%

A light source emits monochromatic light of wavelength 555nm. The source consumes 100W of electric power and emits 35W of radiant flux. Calculate the overall luminous efficiency.

A battery-operated torch is adjusted to send an almost parallel beam of light. It produces an illuminance of 40 lux when the light falls on a wall 2m away. The illuminance produced when it falls on a wall 4m away is close to:

1. 40 lux
2. 20 lux
3. 10 lux
4. 5 lux

Why is the luminous efficiency small for a filament bulb as compared to a mercury vapour lamp?

The luminous flux of a monochromatic source of 1W is 450 lumen/ watt. Find the relative luminosity at the wavelength emitted.

As the wavelength is increased from violet to red, the luminosity:

1. Continuously increases.
2. Continuously decreases.
3. Increases then decreases.
4. Decreases then increases.

A bulb is hanging over a table. At which portion of the table is the illuminance maximum? If a plane mirror is placed above the bulb facing the table, will the illuminance on the table increase?

A source emits 31.4W of radiant flux distributed uniformly in all directions. The luminous efficiency is 60 lumen/ watt. What is the luminous intensity of the source?

The luminous flux of a 1W sodium vapour lamp is more than that of a 10kW source of ultraviolet radiation. Comment.

A point source emitting light uniformly in all directions is placed 60cm above a table-top. The illuminance at a point on the table-top, directly below the source, is 15 lux. Find the illuminance at a point on the table-top 80cm away from the first point.

A source emits light of wavelengths 555nm and 600nm. The radiant flux of the 555nm part is 40W and of the 600nm part is 30W. The relative luminosity at 600nm is 0'6. Find:

1. The total radiant flux.
2. The total luminous flux.
3. The luminous efficiency.

The relative luminosity of wavelength 600nm is 0.6. Find the radiant flux of 600nm needed to produce the same brightness sensation as produced by 120W of radiant flux at 555nm.

A student is studying a book placed near the edge of a circular table of radius R. A point source of light is suspended directly above the centre of the table. What should be the height of the source above the table so as to produce maximum illuminance at the position of the book?

The illuminance of a small area changes from 900 lumen/m² to 400 lumen/m² when it is shifted along its normal by 10cm. Assuming that it is illuminated by a point source placed on the normal, find the distance between the source and the area in the original position.