Note: For systematic learning, you can check the index page of the Instruments in Forensic Science. Here, we listed all the MCQs based on the NTA UGC syllabus.

1. The visible spectrum in EMR has the following range:

1. 3700 – 7800 A°
2. 8000 – 12000 A°
3. 12000 – 18000 A°
4. 18000 – 25000 A°

Answer: (1) 3700 – 7800 A°

Explanation: The visible spectrum in the electromagnetic spectrum is from violet (400 nm) to red (750 nm) (more precisely 3700 – 7800 A°)

2. The ‘fingerprint’ region of IR spectrum can be subdivided into the following except:

1. 1500 – 1350 cm-1
2. 1350 – 1000 cm-1
3. Below 1000 cm-1
4. Below 500 cm-1

Explanation: The fingerprint region (infrared spectrum) ranges from 1450 – 500 cm-1 and this region has an almost unique spectrum for a compound and that is why they are called the fingerprint region.

3. The wavelength of waves associated with electrons accelerated through a potential difference of ‘V’ volts is

1. Directly proportional to V
2. Directly proportional to (V)1/2
3. Inversely proportional to V
4. Inversely proportional to (V)1/2

Answer: (4) Inversely proportional to (V)1/2

Explanation:
de-Broglie wavelength (λ) = h/p
-> h= plank constant (​6.6×10−34) and
-> p=  √(2meV); m= mass of electron, e= charge of electron and V= potential difference.
The final equation will be (λ) = h/√(2meV)
-> Thus, λ is inversely proportional to √V

4. The energy of photon is directly proportional to its :

1. Incident angle
2. Reflection angle
3. Frequency
4. Absorption

Explanation: -> Amount of energy is directly proportional to the photon’s electromagnetic frequency.
-> Amount of energy is equivalently and inversely proportional to the wavelength.

5. A substance that behaves in the same way as light polarised in any direction is

1. Isotropic
2. An isotope
3. Anisotropic
4. Divergent

Explanation: -> Isotropic: the velocity of light or the refractive index does not vary with the direction in the substance.
-> Anisotropic: Variable velocity of light and RI with the direction.

6. NAA measures the characteristic energy values of the following rays emitted by radioactive isotope:

1. Alpha rays
2. Beta rays
3. Gamma rays
4. X-rays

Explanation: -> In NAA, a coaxial detector is used to measure the gamma–rays with energies over the range from about 60 keV to 3.0 MeV.
-> Geiger-Mueller (GM) detector is used to detect alpha, beta, and gamma radiation.

7. Assertion (A): The nature of all electromagnetic radiations is the same.

Reason (R): They differ only in frequency and wavelength and in the effect they produce in matter.

1. Both (A) and (R) are correct
2. (A) is correct, but (R) is incorrect
3. Both (A) and (R) are incorrect
4. (A) is incorrect, but (R) is correct

Answer: (1) Both (A) and (R) are correct

Explanation: All electromagnetic waves are transverse waves that travel at 3 lakhs km/s. The only difference is the wavelength and how they affect the matter.

8. Beer’s and Lambert Law is the basic principle in

1. TLC
2. Spectrophotometry
3. Neutron Activation Analysis
4. X-ray

Explanation:
-> Beer-Lambert law states the linear relationship between the concentration and absorbance of the solution which enables the concentration determination by measuring its absorbance.
-> Spectrophotometry is a method for determining how much light is reflected (or absorbed, emitted) by a chemical material over a certain wavelength.
-> So, one can say that the basic principle of spectrophotometry is absorption that governs by Beers and Lambert law.

9. Apart from Beer’s law, another limiting law in chemistry is:

1. Michelson law
2. Debye-Huchel law
3. Planks law
4. Maxwell law

Explanation:
-> Debye Huckel Limiting Law states that the activity of an ion in an aqueous solution is inversely proportional to the square root of the ionic strength of the solution.
-> It is applicable only for a dilute solution, so it is called the limiting law.

10. The full name of N.M.R. is

1. Nuclear Magnetic Resolution
2. Nuclear Magnetic Remittance
3. Nuclear Magnetic Resonance
4. Nuclear Magnetic Resistance

11. Radio frequency falls in which of the following wavelength region of EMR?

1. 100 to 0.1 m
2. 100 to 1 mm
3. 200 to 800 mm
4. 2 to 0.1 mm

Answer: (1) 100 to 0.1 m

12. Soft X ray are useful for the examination of

(i) Paintings (ii) Jewellery (iii) Hidden Objects (iv) Loaded Dices

1. (i) and (iii)
2. (ii) and (iii)
3. (iii) and (iv)
4. (i) and (ii)

Answer: (4) Both Paintings and Jewellery

13. The working of Polilight is based on ______.

1. Alternate light source
2. U.V. light source

Explanation: Polilight is a portable, high-intensity, and alternative light source that is used to detect various evidences at the scene of crime. Evidences such as fingerprints, bodily fluids, and other trace evidence can be easily be seen using this alternate light source.

14. Which of the following statements is not true?

1. The chemical and physical effects of various electromagnetic radiations are quite similar.
2. The potential energy of an atom depends on the electronic configuration.
3. Molecular spectra are much more complicated than those of atomic spectra.
4. X-rays cause the ejection of inner electrons from matter.

Answer: (2) The potential energy of an atom depends on the electronic configuration.

Explanation:
-> Statement 1 [True]: All electromagnetic waves are transverse waves that travel at 3 lakhs km/s. The only difference is the wavelength (or frequency).
-> Statement 2 [False]: The potential energy is independent of the direction in space and depends only on the distance between the electron and the nucleus.
-> Statement 3 [True]: because molecules can also vibrate and rotate, the energies associated with those motions are needed to study separately.
-> Statement 4 [True]: X-rays cause the ejection of inner electrons from matter and create a vacancy in the inner shell of that atom.

15. Which of the following statements is not correct for a spectrophotometer?

1. Decreasing the slit width will increase noise
2. Noise will increase with the age of source
3. Decreasing the slit width will decrease noise
4. Noise will depend on the wavelength being used

Answer: (3) Decreasing the slit width will decrease noise

Explanation:
-> Decreasing the slit width will increase noise because both, thermal noise and shot noise (from discrete nature of electric charge), increase with signal strength decreases. And signal strength decreases with a decrease in slit width. Hence, an increase in noise.
-> As the age of the sources increases, the resultant drop in power output is seen which increases the relative noise.
-> Noise will depend on the wavelength being used because the power output of the system is also a function of wavelength. So, either power drop or raise is seen which again is proportional to the respective noise level.
-> Silt: Slit has a rectangular aperture through which light enters into and exits from the monochromator that controls the spectral resolution (ability to separate close wavelengths).
-> Slit Width is the width of the entrance and exit slits of the monochromator which are expressed in mm.
Reference Book: Analytical Instrumentation: Performance Characteristics and Quality By Graham Currell

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