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Solar Energy Multiple Choice Questions on “Measurements of Solar Radiation – 2”.
1. What is the Angstrom compensation pyrheliometer used to measure?
a) Direct solar radiation
b) Indirect solar radiation
c) Diffused solar radiation
d) UV radiation
Answer: a
Clarification: Angstrom compensation pyrheliometer is used to measure direct solar radiation. It is one of the standard equipment for the process. UV radiation is generally measured by pyranometer.
2. What is the main difference between pyranometer and pyrheliometer?
a) Both measure solar radiation
b) Pyranometer measures global radiation while pyrheliometer measures direct solar radiation
c) Pyranometer and pyrheliometer measure global radiation
d) Pyranometer measures solar radiation while pyrheliometer measures global radiation
Answer: b
Clarification: The main difference pyranometer and pyrheliometer is the purpose of measurement. Pyranometer is used to measure global solar radiation and hence it is used for both visible and UV. Pyrheliometer is used to measure direct solar radiation.
3. What is the main advantage of sunshine recorder?
a) It is more sophisticated than pyranometers and pyrheliometers
b) It is more expensive than pyranometers and pyrheliometers
c) It is less accurate but inexpensive
d) It is less accurate but extremely expensive
Answer: c
Clarification: The main advantage of a sunshine recorder is that it is inexpensive. However, it is less accurate as well. Also, it is not as sophisticated as pyranometers and pyrheliometers.
4. How does a sunshine recorder work?
a) Measures the solar irradiance
b) Measures the solar radiation
c) Measures the number of hours of sunshine
d) Measures the number of hours of sunshine above a certain threshold
Answer: d
Clarification: A sunshine recorder works by measuring the number of hours during which sunshine is above a certain threshold. The threshold is typically set at 200 mW/cm2. The data collected can be used to determine the solar insolation.
5. Which of the following best describes the measurement process in a pyrheliometer?
a) Sunlight → window in pyrheliometer → thermopile → heat is converted to electrical signal → recorded
b) Sunlight → window in pyrheliometer → heat is converted to electrical signal → thermopile → recorded
c) Window in pyrheliometer → sunlight → thermopile → heat is converted to electrical signal → recorded
d) Sunlight → heat is converted to electrical signal → window in pyrheliometer → thermopile → recorded
Answer: a
Clarification: Sunlight enters inside the pyrheliometer through a window. This sunlight is directed onto a thermopile which then converts into an electrical signal. This electrical can be recorded and mapped to a corresponding intensity.
6. Thermopile is a collection of _______
a) thermocouples connected in parallel
b) thermocouples connected in series
c) reflectors connected in series
d) reflectors connected in parallel
Answer: b
Clarification: Thermopile is a collection of thermocouples, usually connected in series. It works on the principle of thermoelectric effect – generating a voltage when dissimilar metals are exposed to temperature difference.
7. What is the irradiation proportional to in thermopile technology?
a) Difference between sun exposed area and shadow area
b) Difference between temperature of sun exposed area and shadow area
c) Difference between temperature of sun exposed area and temperature of shadow area
d) Difference between of sun exposed area and temperature of shadow area
Answer: c
Clarification: In thermopile technology, irradiation is proportional to the difference between temperature of sun exposed area and shadow area. A thermopile pyranometer consists of a sensor based on thermopiles.
8. Which portion of the solar spectrum can a photodiode-based pyranometer detect?
a) 100 – 200nm
b) 1 – 10um
c) 150 – 200nm
d) 400 – 900 nm
Answer: d
Clarification: Photodiode-based pyranometer detects the portion of solar spectrum between 400 – 900nm. The best ones detect between 350 – 1100nm. Since it uses silicon technology, photodiode-based pyranometers are also called as silicon pyranometers.
9. Photodiode works on the principle of _______
a) photoelectric effect
b) LED
c) thermocouple
d) differential resistance
Answer: a
Clarification: Photodiode works on the principle of photoelectric effect. Photoelectric effect is the emission of electrons when electromagnetic radiation hits the surface of a material (generally a metal).
10. What does the net radiometer measure?
a) Measures the incoming solar radiation
b) Measures the difference between incoming and outgoing radiation
c) Measures the sum of incoming and outgoing radiation
d) Measures the outgoing solar radiation
Answer: b
Clarification: As the name suggests, a net radiometer measures the difference between incoming and outgoing radiation. Hence, it is used to the “net radiation” (NR) at the earth’s surface.
11. Which of the following technology does a net radiometer work on?
a) Semiconductor
b) Conductor-insulator
c) Thermopile sensor
d) Photoelectric effect
Answer: c
Clarification: A net radiometer is based on a thermopile sensor which works on Seebeck effect. It basically measures the temperature difference between two receivers. Photodiode based pyranometer uses semiconductor technology.
12. What is a bolometer made up of?
a) A thermal reservoir and a metal layer
b) An electrical reservoir and an insulated layer
c) An absorptive element, thermal reservoir and a thermally insulated material linking both of them
d) An absorptive element, thermal reservoir and a thermal link
Answer: d
Clarification: A bolometer is a physical device used to measure power of incident electromagnetic radiation. It consists of an absorptive element such as a metal layer, a thermal reservoir and a thermal link connecting both of them.
13. Which of the following best describes the working of bolometer?
a) Radiation → temperature of absorptive element increases above the thermal reservoir → resistive thermometer to measure temperature change
b) Radiation → resistive thermometer to measure temperature change → temperature of absorptive element increases above the reservoir
c) Temperature of absorptive element increases above the reservoir → radiation → resistive thermometer to measure temperature change
d) Radiation → temperature of absorptive element increases above the electrical reservoir → resistive thermometer to measure temperature change
Answer: a
Clarification: When any radiation is incident on a bolometer, the absorptive element absorbs the radiation and raises its temperature above that of the thermal reservoir. The temperature change can be directly measured by connecting a resistive thermometer.
14. In a bolometer, the greater the absorbed power, higher the temperature.
a) True
b) False
Answer: a
Clarification: In a bolometer, the greater the absorbed power, higher the temperature. This is evident because as the absorptive element absorbs more power, it further raises its temperature. The intrinsic thermal time constant sets the speed of the detector.
15. Bolometers are used for ionizing particles, photons and non-ionizing particles.
a) True
b) False
Answer: a
Clarification: Bolometers are used for ionizing particles, photons and non-ionizing particles. This is because they are directly sensitive to the energy left inside the absorber.
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