MCQs on Photometry
- What is the power of the lamp if its luminous efficiency is 2 lumen/watt and its luminous intensity is 42 candela?
- 62 W
- 138 W
- 76 W
- 264 W
Answer: (d) 264 W
- In a movie hall, if the distance between the screen and the projector is increased by 1% what happens to the illumination on the screen?
- Increases by 1%
- Decreases by 1%
- Increases by 2%
- Decreases by 2%
Answer: (d) Decreases by 2%
- At a height of one meter above the centre of a circular table of diameter 4m, a bulb of 100 W hangs. If the intensity at a point on its rim is I0, then what is the intensity at the centre of the table?
- Lux is a unit of which of the following?
- Illuminance on a surface
- Luminous intensity of a source
- Luminous efficiency of the source of light
- Transmission coefficient of a surface
Answer: (a) Illuminance on a surface
- Lux is equivalent to which of the following?
- 1 candela/m2
- 1 lumen/cm2
- 1 lumen/m2
- 1 candela/cm2
Answer: (a) 1 candela/m2
- If a lamp has a luminous efficiency of Five lumen/watt and a luminous intensity of 35 candela. What is the power of the lamp?
- 176 W
- 88 W
- 36 W
- 80 W
Answer: (b) 88 W
- The distance between a point source of light and a screen is 60 cm and now this distance is increased to 180 cm. By how many fractions will the intensity on the screen change as compared to the original intensity?
- 9 times
- 3 times
- (1/9) times
- (1/3) times
Answer: (c) (1/9) times
- Venus looks brighter than other stars because
- it has no atmosphere
- atomic fission occurs on its surface
- it has a higher density than other stars
- it is closer to earth than most stars
Answer: (d) it is closer to earth than most stars
- Which of the following sources of light is the inverse square law valid for?
- Cylindrical source
- Isotropic point source
- All types of light sources
Answer: (c) Isotropic point source
- Which of the following has more luminous efficiency?
- 40 W fluorescent tube
- 40 W bulb
- Both have the same luminous efficiency
- Cannot say
Answer: (a) 40 W fluorescent tube
- A lamp hangs at a height of 4 m above a table. The lamp is lowered by 1 m. By how much will the illuminance increase?
Answer: (a) 78%
- A point source of 100 candela is held 5 m above a sheet of blotting paper which reflects 75% of the incident light. What is the illuminance of blotting paper?
- 4 lux
- 4 phot
- 3 lux
- 3 phot
Answer: (a) 4 lux