Related InterviewSolutions

• The illuminance of a small -2 area changes from 900 lumen m^-2 to 400 lumen m^-2 when it is shifted along its normal by 10 cm. 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.
• 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(a) I∝ 1/r(b) I ∝ 1/r2(c) I ∝ 1/r3(d) I ∝ 1/r4
• Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of 60°, by what fraction will the illuminance change ?
• 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 2 m away. The illuminance produced when it falls on a wall 4 m away is close to(a) 40 lux(b) 20 lux(c) 10 lux(d) 5 lux.
• 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(a) 0.5%(b) 1%(c) 2%(d) 4%.
• A source emits light of wavelengths 555 nm and 600nm. The radiant flux of the 555 nm part is 40 W and of the 600 nm part is 30 W. The relative luminosity at 600 nm is 0.6. Find (a) the total radiant flux, (b) the total luminous flux, (c) the luminous efficiency.
• A circular area of radius 1.0 cm is placed at a distance of 2.0 m from a poit source.Teh source emits light uniformluy in al directions. The line joining the sorce to the dcentre of the area is normal to the area. It ils found that `2.0xx1^-3` lumen of luminous flux is incident on the area. Calculate the total luminous flux emitted by the soure and teh luminous intensity of the source along the axis of the area.
• Figure shows a small diffused plane source S placed over a horizontal table-top at a distance of 2.4 m 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 1.8 m from A.
• Using figure (22.1), find the relative luminosity of wavelength (a) 480 nm, (b) 520 nm (c ) 580 nm and (d) 600 nm.
• In the grease spot photometer, a lamp with dirty chimney is found to balance an electric lamp of constant illuminating power at a distance of `0.1` m from the spot. When the chimney is cleaned, the electric lamp has to be shifted by 2 cm to obtain a balance. Calculate the precentage of light absorbed by the dirty chimney