# Biomedical Instrumentation Questions and Answers – Methods of Monitoring Foetal Heart Rate – 2

This set of Biomedical Instrumentation Multiple Choice Questions & Answers focuses on “Methods of Monitoring Foetal Heart Rate – 2”.

1. The energy must be reflected and returned through a single 30° prism, so that it passes through the prism in both directions is called __________
a) Cornu mounting
b) Mono mounting
c) Littrow mounting
d) Trio mounting

Explanation: Quartz shows the property of double refraction. Therefore, two pieces of quartz, one right-handed and one left handed are taken and cemented back-to-back in the construction of 60° prism (Cornu mounting), or the energy must be reflected and returned through a single 30° prism, so that it passes through the prism in both directions (Littrow mounting).

2. Most modern instruments now use a _______ as a dispersing element in the monochromator.
a) Prism monochromators
b) Holographic gratings
c) Diffraction gratings
d) Replica gratings

Explanation: Most modern instruments now use a diffraction grating as a dispersing element in the monochromator, as prisms in general have a poorer stray light performance and require complex precision cams to give a linear wavelength scale. Replica gratings can even be produced more cheaply than prisms and require only a simple sine bar mechanism for the wavelength scale.

3. A typical reflection grating may have 1200 grooves/mm, which means the grooves are spaced at about _______ intervals.
a) 800 nm
b) 600 nm
c) 860 nm
d) 680 nm

Explanation: A typical reflection grating may have 1200 grooves/mm, which means the grooves are spaced at about 800 nm intervals. The grating may have a width of 20 mm or more, giving a total of at least 24,000 grooves.

4. What is reproduced from a master holographic grating by moulding its grooves onto a resin surface or silica substrate?
a) Diffraction grating
b) Replica grating
c) Silicate glasses
d) Fused silica

Explanation: Holographic gratings used in commercial spectrophotometers are either original master gratings produced directly by an interferometer or are replica gratings. Replica gratings are reproduced from a master holographic grating by moulding its grooves onto a resin surface on a glass or silica substrate.

5. What is the utilization wavelength limit for quartz?
a) 300 nm
b) 350 nm
c) 180 nm
d) 210 nm

Explanation: Normally, the absorbance of any material should be less than 0.2 at the wavelength of use. Below 300 nm, quartz or fused silica is utilized. The limit for quartz is 210 nm.
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6. Which material is used to reduce the reflections from glass surfaces?
a) Manganese Flouride
b) Magnesium oxide
c) Magnesium Flouride
d) Manganese oxide

Explanation: Reflections from glass surfaces are reduced by coating these with magnesium fluoride, which is one-quarter wavelength in optical thickness. With this, scattering effects are also greatly reduced.

7. With the use of _______ chromatic aberrations and other imperfections of the lenses are minimized.
a) Lenses
b) Mirrors
c) Slits
d) Diaphragm

Explanation: To minimize light losses, lenses are sometimes replaced by front-surfaced mirrors to focus or collimate light beam in absorption instruments. Mirrors are aluminized on their front surfaces. With the use of mirrors, chromatic aberrations and other imperfections of the lenses are minimized.

8. _______ are often used for splitting the beam.
a) Multilayer coated lenses
b) Silvered films
c) Silicate glasses
d) Half-silvered mirrors

Explanation: The two beams must retain the spectral properties of the incident beam. Half-silvered mirrors are often used for splitting the beam. However, they absorb some of the light in the thin metallic coating. Beam splitting can also be achieved by using a prismatic mirror or stack of thin horizontal glass plates, silvered on their edges and alternatively oriented to the incident beam.

9. The sample holder is generally inserted somewhere in the interval between the ______and _______
a) Silvered film and multi-layered coating
b) The light source and the detector
c) The light source and silvered film
d) Silvered film and the detector

Explanation: Gases may be contained in cells which are sealed or stoppered to make them air-tight. The sample holder is generally inserted somewhere in the interval between the light source and the detector. For the majority of analyses, a 10 mm path-length rectangular cell is usually satisfactory.

10. In sample holders, for such applications, a 50 cm path-length with about a ________ volume cell is employed.
a) 0.3 ml
b) 3 liters
c) 0.3 liters
d) 3 ml

Explanation: Studies of dilute or weakly-absorbing liquid samples, or of samples where trace components must be detected, require a cell with a long path-length. For such applications, a 50 cm path-length with about a 300 ml volume cell is employed.

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