This set of Biomedical Instrumentation Multiple Choice Questions & Answers (MCQs) focuses on “Photoelectric Transducers”.
1. What is the principle behind photoelectric transducers?
a) conversion of wind energy to electrical energy
b) conversion of light energy to electrical energy
c) conversion of mechanical energy to electrical energy
d) conversion of electrical energy to light energy
Explanation: Photoelectric transducers are based on the principle of conversion of light energy into electrical energy. This is done by causing the radiation to fall on a photosensitive element and measuring the electrical current so generated with a sensitive galvanometer directly or after suitable amplification.
2. Which of the following material is used to build photovoltaic cells ?
Explanation: Photovoltaic or barrier layer cells usually consist of a semiconducting substance, which is generally selenium deposited on a metal base which may be iron and which acts as one of the electrodes. The semiconducting substance is covered with a thin layer of silver or gold deposited by cathodic deposition in vacuum. This layer acts as a collecting electrode.
3. Selenium cells are sensitive to almost the entire range of wavelengths of the spectrum.
Explanation: Selenium cells are sensitive to almost the entire range of wavelengths of the spectrum. However, their sensitivity is greater within the visible spectrum and highest in the zones near to the yellow wavelengths.
4. Which of the following is not a photoemissive cell?
a) high vacuum photocells
b) barrier layer cell
c) gas-filled photocell
d) photomultiplier tubes
Explanation: Barrier layer cells are photovoltaic cells. They consist of a semiconducting substance, which is generally selenium deposited on a metal base which may be iron and which acts as one of the electrodes. Photovoltaic cells are very robust in construction, need no external electrical supply and produce a photocurrent sometimes stronger than other photosensitive elements.
5. Photo-diodes work in ____
a) forward biased
b) reverse biased
c) independent of forward and reverse biasing
d) any configuration
Explanation: The photodiode is a P-N junction semiconductor diode. It always operated in the reversed biased condition. The light is always focused through a glass lens on the junction of the photo diode.
6. Photovoltaic cells need external electrical supply to function?
Explanation: Photovoltaic cells are very robust in construction, need no external electrical supply and produce a photocurrent sometimes stronger than other photosensitive elements. Typical photocurrents produced by these cells are as high as 120 mA/lumen. At constant temperature, the current set up in the cell usually shows a linear relationship with the incident light intensity.
7. The instruments which give direct reading of the temperature at the thermistor position are known as _________
Explanation: The instruments which give direct reading of the temperature at the thermistor position are known by the name telethermometers. This is because of their ability to use leads which are hundreds of feet long without a significant decrease in accuracy. The continuous signal is also suitable for recording without amplification.
8. Which of the following is a photoemissive cell ?
a) photomultiplier tubes
b) barrier layer cell
c) galvanic cell
d) rochell-salt cell
Explanation: Photomultiplier tubes are photoemissive cells. These type to cells do require an external power supply to provide a sufficient potential difference between the electrodes to facilitate the flow of electrons generated at the photosensitive cathode surface. Also, amplifier circuits are invariably employed for the amplification of this current.
9. Cesium-silver oxide cells are sensitive to the near infrared wavelengths.
Explanation: Cesium-silver oxide cells are sensitive to the near infrared wavelengths. Potassiumsilver oxide and cesium-antimony cells have maximum sensitivity in the visible and ultraviolet regions. The spectral response also depends partly on the transparency to different wavelengths of the medium to be traversed by the light before reaching the cathode.
10. Thermister is used to measure ____________
Explanation: Thermistor is used to measure temperature. It is a temperature transducer. With change in temperature its resistance changes. Thus its working principle is variable resistance. Thermistors are the oxides of certain metals like manganese, cobalt and nickel which have large negative temperature coefficient, i.e. resistance decreases with increase in temperature.
Sanfoundry Global Education & Learning Series – Biomedical Instrumentation.
To practice all areas of Biomedical Instrumentation, here is complete set of 1000+ Multiple Choice Questions and Answers.