# Analytical Instrumentation Questions and Answers – Introduction to UV Visible Spectrometers

This set of Analytical Instrumentation Interview Questions and Answers focuses on “Introduction to UV Visible Spectrometers”.

1. Beer’s law states that the intensity of light decreases with respect to ___________
a) Concentration
b) Distance
c) Composition
d) Volume

Explanation: According to Beer’s law, the intensity of light diminishes as the medium’s concentration increases. Beer made the statement.

2. Lambert’s law states that the intensity of light decreases with respect to __________
a) Concentration
b) Distance
c) Composition
d) Volume

Explanation: Lambert’s law indicates that light intensity falls as the concentration of the medium increases. Lambert made the statement.

3. The representation of Beer Lambert’s law is given as A = abc. If ‘b’ represents distance, ‘c’ represents concentration and ‘A’ represents absorption, what does ‘a’ represent?
a) Intensity
b) Transmittance
c) Absorptivity

Explanation: ‘a’ represents the absorption constant. It is also known as absorptivity.

4. Which of the following is not true about Absorption spectroscopy?
a) It involves transmission
b) Scattering is kept minimum
c) Reflection is kept maximum
d) Intensity of radiation leaving the substance is an indication of a concentration

Explanation: In absorption spectroscopy, reflection and scattering must both be kept to a minimum. Absorption is proportional to the number of molecules in the substance.

5. Transmittance is given as T = P/Po. If Po is the power incident on the sample, what does P represent?
a) Radiant power transmitted by the sample
b) Radiant power absorbed by the sample
c) Sum of powers absorbed and scattered
d) Sum of powers transmitted and reflected

Explanation: The sample’s radiant power is denoted by the letter P. The ratio of radiant power transferred by the sample to radiant power incident on it is known as transmittance.

6. What is the unit of absorbance which can be derived from Beer Lambert’s law?
a) L mol-1 cm-1
b) L gm-1 cm-1
c) Cm
d) No unit

Explanation: There is no unit for absorbance. Absorptivity, distance, and concentration units cancel each other out. As a result, there is no unit for absorption.

7. What is the unit of molar absorptivity or absorptivity which is used to determine absorbance A in Beer Lambert’s formula?
a) L mol-1 cm-1
b) L gm-1 cm-1
c) Cm
d) No unit

Explanation: The unit of absorptivity is L mol-1 cm-1. If concentration is represented as gm per litre it becomes L gm-1 cm-1.

8. Beer Lambert’s law gives the relation between which of the following?
c) Energy absorption and concentration
d) Energy absorption and reflected radiation

Explanation: The relationship between energy absorption and concentration is given by Beer Lambert’s law. Beer and Lambert were the ones who proposed it.

9. In which of the following ways, absorption is related to transmittance?
a) Absorption is the logarithm of transmittance
b) Absorption is the reciprocal of transmittance
c) Absorption is the negative logarithm of transmittance
d) Absorption is a multiple of transmittance

Explanation: The ratio of the radiant power transmitted by a sample to the radiant power incident on the sample is known as transmittance. The negative logarithm of transmittance is absorption.

10. Which of the following is not a limitation of Beer Lambert’s law, which gives the relation between absorption, thickness and concentration?
a) Concentration must be lower
b) Radiation must have higher bandwidth
c) Radiation source must be monochromatic
d) Does not consider factors other than thickness and concentration that affect absorbance

Explanation: The law is derived with monochromatic radiation in mind. As a result, as bandwidth expands, deviation occurs.

UV-visible (UV-Vis) spectrophotometry is a technique for measuring light absorbance in the ultraviolet and visible wavelength ranges of the electromagnetic spectrum. Incident light can be absorbed, reflected, or transmitted as it strikes materials. UV–Vis spectroscopy, also known as ultraviolet–visible spectrophotometry (UV–Vis or UV/Vis), is the study of absorption and reflectance spectroscopy in the ultraviolet and visible parts of the electromagnetic spectrum. This means it makes use of visible and neighbouring light.