Photometry Physics - Photometry

The yellow colour has a greater luminous efficiency as compared to the other colours. Can we increase the illuminating power of a white light source by putting a yellow plastic paper around this source?

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

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?

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

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.

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 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.

A source emits 45 joules of energy in 15s. What is the radiant flux of the source?

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

Figure shows a small diffused plane source S placed over a horizontal table-top at a distance of 2.4m with its plane parallel to the table-top. The illuminance at the point A directly below the source is 25 lux. Find the illuminance at a point B of the table at a distance of 1.8m from A.

A photographic plate is placed directly in front of a small diffused source in the shape of a circular disc. It takes 12s to get a good exposure. If the source is rotated by 60° about one of its diameters, the time needed to getthe same exposure will be:

1. 6s
2. 12s
3. 24s
4. 48s.

The one parameter that determines the brightness of a light source sensed by an eye is:

1. Energy of light entering the eye per second.
2. Wavelength of the light.
3. Total radiant flux entering the eye.
4. Total luminous flux entering the eye.

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.