About Photometry

Photometry is the measurement of light, defined as electromagnetic radiation that can be detected by the human eye. Photometry is distinct from other measurements of light in the optical field, such as radiometry, which is the science of measuring electromagnetic radiation, including visible light. Photometry is generally based on the eye's photopic response, and thus photometric measurements cannot accurately determine a sources perceived brightness under low-light conditions, when colors are undetectable, like only moonlight or starlight. Photometry is the science and technology of quantifying and measuring light properties related to their perceived brightness to human eyes.

Differential photometry is measuring changes in an object's brightness over time. The measurements are combined in the object's light curve. When measuring an object's brightness across multiple images taken over time, compared stars should be used. When performing photometry, a circle, often called a lens, is placed around each star for which the brightness is to be measured. A general outline of the visual average of human eyesight would be required if any methods were to be developed for measuring or reproducing the colour of the light.

The Photometry short course at NIST covers fundamentals in photometry, radiometry, and colorimetry, and the practical aspects of measuring the light flux, luminous intensity, illuminance, luminosity, color temperature, and chroma of a light source.

Following are some of the multiple choice questions on the Photometry with answers that will help the students in developing their knowledge.

Photometry MCQ

1. In Flame photometry, Flame color’s intensity tells about

  • how much of the element present
  • Number of compound present
  • complex structure of compound
  • none of above

2. Which of the following is the advantage of grating monochromators?

  • Dispersion is non-overlapping
  • Dispersion occurs in non-linear manner
  • Dispersion is overlapping
  • Dispersion occurs in a linear manner

3. Which of the following is the advantage of prism monochromators?

  • Dispersion is non-overlapping
  • Dispersion occurs in non-linear manner
  • Dispersion is overlapping
  • Dispersion occurs in a linear manner

4. Laminar flow burner used in Flame photometers is also known as

  • Turbulent burner
  • Premix burner
  • Total consumption burner
  • Nozzle mix burner

5. Which of the following is disadvantage of Laminar flow burner used in Flame photometry?

  • Noiseless
  • Stable flame for analysis
  • Efficient atomization of sample
  • Sample containing two or more solvents can be burned efficiently

6. In Flame emission photometers, the measurement of _____________ is used for qualitative analysis.

  • Colour
  • Intensity
  • Velocity
  • Frequency

7. Which of the following is the principle of Flame emission photometers?

  • Radiation is absorbed by non-excited atoms in vapour state and are excited to higher states
  • Medium absorbs radiation and transmitted radiation is measured
  • Colour and wavelength of the flame is measured
  • Only wavelength of the flame is measured

8. The elements like gold, silver, & inert gases are not analyzed by flame photometry because

  • They need higher amount of energy for excitation than 1st and 2nd group.
  • They need lesser amount of energy for excitation than 1st and 2nd group.
  • not related to energy
  • depends on molecular weight

9. Flame photometry is mainly used for,

  • 1st and 2nd group elements
  • 3rd and 4th group elements
  • Whole periodic table
  • none of this

10. In Flame emission photometers, the measurement of _____________ is used for quantitative analysis.

  • Intensity
  • Colour
  • Frequency
  • Velocity

11. Phototubes are more sensitive than photovoltaic cells

  • True
  • False

12. Which of the following is not an application of Flame emission photometers?

  • Analysis of biological fluids
  • Analysis of complex mixtures
  • Determination of metals such as Mn, Cu
  • Determination of sodium, potassium in soil

13. 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?

  • 2√5Io
  • 5√5Io
  • 2Io
  • None of these

14. What is the power of the lamp if its luminous efficiency is 2 lumen/watt and its luminous intensity is 42 candela?

  • 62 W
  • 78 W
  • 128 W
  • 264 W

15. Lux is equivalent to which of the following?

  • 1 lumen/cm2
  • 1 lumen/m2
  • 1 candela/cm2
  • 1 candela/m2

16. Which of the following has more luminous efficiency?

  • 40 W bulb
  • 40 W fluorescent tube
  • 100 W bulb
  • None of these

17. 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?

  • 92%
  • 40%
  • 64%
  • 78%

18. 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?

  • 3 lux
  • 3 phot
  • 4 lux
  • 4 phot

19. Which of the following sources of light is the inverse square law valid for?

  • Cylindrical source
  • Isotropic point source
  • Searchlight
  • None of these

20. Which is application of flame photometry ?

  • To study of chemical structure
  • To determine functional group
  • To assay of drug
  • To estimate metalic ions like sodium, potassium, etc.

21. Which of the following is not an advantage of Laminar flow burner used in Flame photometry?

  • Noiseless
  • Stable flame for analysis
  • Efficient atomization of sample
  • Sample containing two or more solvents can be burned efficiently

22. Which is not application of flame photometry

  • To estimate sodium, magnesium, calcium
  • Assay of metformin.
  • Used to determine magnesium and calcium in cement.
  • To detected metallic ions in sample

23. Flame photometry is used for the determination of compositional analysis of_______________?

  • Solids
  • Alkali metals
  • Natural gas
  • Isotopes

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