This set of Engineering Materials and Metallurgy Questions and Answers for Aptitude test focuses on “Pyrometry and the Types of Pyrometers”.
1. What is the most widely used method for metallurgical temperature measurement?
a) Thermoelectric pyrometer
b) Optical pyrometer
c) Radiation pyrometer
d) Recording pyrometer
View Answer
Explanation: The most widely preferred method of measurement and control of metallurgical temperature is the thermoelectric pyrometer. It can be used up to a temperature of 3000 F. It consists of a thermocouple, junction block, extension leads, and a recorder.
2. The total emf of the thermoelectric pyrometer is given as ___________
a) Peltier effect
b) Thomson effect
c) Seebeck effect
d) Joule’s method
View Answer
Explanation: Generation of an emf due to the contact between two dissimilar metals or wires is called Peltier effect. The generation of an emf due to a temperature difference due to opposing ends of the same wire is Thomson effect. The algebraic sum of these four emfs is known as Seebeck effect.
3. The cold junction in a thermoelectric pyrometer is maintained at ________
a) 12 F
b) 32 F
c) 55 F
d) 80 F
View Answer
Explanation: The Peltier effect of thermoelectric pyrometer involves emf at the hot and cold junctions, whereas Thomson effect deals with emfs along each wire. The cold junction must be kept at a constant temperature of 0oC or 32 F.
4. Chromel-Alumel can be used at a temperature range of __________
a) 300-1400 F
b) 420-600 F
c) 800-1000 F
d) 1200-2200 F
View Answer
Explanation: Thermoelectric pyrometer makes use of dissimilar materials for the metallic wires to develop an emf. Chromel-Alumel is a commonly used material containing chromel (nickel and chromium) and alumel (nickel, manganese, aluminum, silicon). It is useful at a temperature range of 1200-2200 F.
5. Constantan is an alloy containing _________
a) Nickel and aluminum
b) Silicon, manganese, and aluminum
c) Copper and nickel
d) Aluminum and manganese
View Answer
Explanation: Thermoelectric pyrometer makes use of dissimilar materials for the metallic wires to develop an emf. One such material is Iron-Constantan. Constantan is an alloy containing 54% copper and 46% nickel. It is useful at a temperature range of 300-1400 F.
6. What is the advantage of copper-constantan over iron-constantan?
a) Low density
b) Low coefficient of expansion
c) Low-temperature measurement
d) Elevated temperature difference
View Answer
Explanation: Copper-constantan differs from iron-constantan due to the use of copper instead of iron, along with the possible addition of manganese and iron. This is useful for measuring low temperatures up to -420 F and a maximum limit of 600 F.
7. Which material is used when radiation pyrometers don’t produce a satisfactory result?
a) Chromel-Alumel
b) Iron-Constantan
c) Copper-Constantan
d) Rhodium-Platinum
View Answer
Explanation: 10% Rhodium-Platinum is a noble-metal thermocouple used for measuring very high temperatures. It can be used in a temperature range of 32-3200 F. These are used when radiation or optical pyrometers do not perform satisfactorily.
8. __________are used as protecting tubes in thermocouples above 2000 F.
a) Wrought iron
b) 14% chrome iron
c) Nichrome
d) Porcelain
View Answer
Explanation: Thermocouples are often covered using protecting tubes. Wrought iron or cast iron can be used as a protecting tube up to 1300 F. 14% chrome iron is used up to 1500 F, whereas 28% chrome iron or nichrome is used up to 2000 F. Above this temperature, porcelain or silicon carbide tubes are used.
9. Which type of pyrometer uses an electric circuit?
a) Controlling pyrometer
b) Optical pyrometer
c) Radiation pyrometer
d) Recording pyrometer
View Answer
Explanation: A recording pyrometer is used to obtain an entire record of the temperature. On the addition of an electric circuit, it may be used to control the flow of gas. Such a device is known as a controlling pyrometer.
10. A radiation pyrometer is based on ___________
a) Planck’s law
b) Stefan-Boltzmann law
c) Rayleigh-Jeans law
d) Sakuma-Hattori equation
View Answer
Explanation: The principle of radiation pyrometer is based on a standard radiation body known as a blackbody. These pyrometers are calibrated to indicate blackbody or true temperature. The Stefan-Boltzmann law expresses the rate of radiation energy.
11. What does Stefan-Boltzmann law for radiation pyrometers denote?
a) W = KT4
b) W = KT
c) W = KT-4
d) W = K/T4
View Answer
Explanation: The principle of radiation pyrometer is based on a standard radiation body known as a blackbody. By Stefan-Boltzmann law, W = KT4 expresses the rate of radiation energy as a proportional to the fourth power of absolute temperature. Here W is the rate of energy emitted and K is a constant of proportionality.
12. What is the maximum usable temperature of radiation pyrometers?
a) 1000 F
b) 5000 F
c) 10000 F
d) No limit
View Answer
Explanation: The radiation pyrometer does not require direct contact with the hot body. Therefore, the upper limit for temperature is not limited by the ability to withstand high temperatures. The lower limit is 1000 F, whereas by using proper stops there is no upper limit temperature.
13. What can be done to increase the temperature range of optical pyrometers?
a) Better accuracy of telescope
b) Using electrical circuit for control box
c) Inclusion of absorbing screen
d) Using red filter
View Answer
Explanation: Optical pyrometers have a temperature range of 1400-2400 F. This range can be improved by using an absorbing screen between the lens and the filament. Therefore, by using various absorbing screens the range can be increased to be over 10000 F.
14. What can be done to make the color comparison better for an optical pyrometer?
a) Better accuracy of telescope
b) Using electrical circuit for control box
c) Inclusion of absorbing screen
d) Using red filter
View Answer
Explanation: An optical pyrometer measures temperature by comparing brightness or the emitted light. To make this comparison easy, a red filter is used. This red filter limits the visible radiation only to the wavelength of red radiation.
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