Photometry MCQs
1. What is the power of the lamp if its luminous efficiency is 2 lumen/watt and its luminous intensity is 42 candela?
A. 62 W
B. 138 W
C. 76 W
D. 264 W
Answer: D. 264 W
2. 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?
A. Increases by 1%
B. Decreases by 1%
C. Increases by 2%
D. Decreases by 2%
Answer: D. Decreases by 2%
4. Lux is a unit of which of the following?
A. Illuminance on a surface
B. Luminous intensity of a source
C. Luminous efficiency of the source of light
D. Transmission coefficient of a surface
Answer: A. Illuminance on a surface
5. Lux is equivalent to which of the following?
A. 1 candela/m2
B. 1 lumen/cm2
C. 1 lumen/m2
D. 1 candela/cm2
Answer: A. 1 candela/m2
6. 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?
A. 176 W
B. 88 W
C. 36 W
D. 80 W
Answer: B. 88 W
7. 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?
A. 9 times
B. 3 times
C. (1/9) times
D. (1/3) times
Answer: C. (1/9) times
8. Venus looks brighter than other stars because
A. it has no atmosphere
B. atomic fission occurs on its surface
C. it has a higher density than other stars
D. it is closer to earth than most stars
Answer: D. it is closer to earth than most stars
9. Which of the following sources of light is the inverse square law valid for?
A. Cylindrical source
B. Searchlight
C. Isotropic point source
D. All types of light sources
Answer: C. Isotropic point source
10. Which of the following has more luminous efficiency?
A. 40 W fluorescent tube
B. 40 W bulb
C. Both have the same luminous efficiency
D. Cannot say
Answer: A. 40 W fluorescent tube
11. 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?
A. 78%
B. 64%
C. 40%
D. 92%
Answer: A. 78%
12. 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?
A. 4 lux
B. 4 phot
C. 3 lux
D. 3 phot
Answer: A. 4 lux
