Mechanical Engineering Principles

276 MECHANICAL ENGINEERING PRINCIPLES

junction, an e.m.f. is produced. This

effect is used in a thermocouple to mea-

sure:

(a) e.m.f. (b) temperature

(c) expansion (d) heat

3. A cold junction of a thermocouple is at
   room temperature of 15°C. A voltmeter
   connected to the thermocouple circuit
   indicates 10 mV. If the voltmeter is cal-
   ibrated as 20°C/mV, the temperature of
   the hot source is:
   (a) 185°C (b) 200°C
   (c) 35°C (d) 215°C


4. The e.m.f. generated by a copper-
   constantan thermometer is 15 mV. If
   the cold junction is at a temperature
   of 20°C, the temperature of the hot
   junction when the sensitivity of the
   thermocouple is 0.03 mV/°Cis:

(a) 480°C (b) 520°C

(c) 20.45°C (d) 500°C

In questions 5 to 12, select the most appro-

priate temperature measuring device from this

list.

(a) copper-constantan thermocouple

(b) thermistor

(c) mercury-in-glass thermometer

(d) total radiation pyrometer

(e) platinum resistance thermometer

(f) gas thermometer

(g) temperature sensitive crayon

(h) alcohol-in-glass thermometer

(i) bimetallic thermometer

(j) mercury-in-steel thermometer

(k) optical pyrometer

5. Over-temperature alarm at about 180°C


6. Food processing plant in the range
   − 250 °Cto+ 250 °C


7. Automatic recording system for a heat
   treating process in the range 90°Cto
   250 °C


8. Surface of molten metals in the range
   1000 °C to 1800°C


9. To calibrate accurately a mercury-in-
   glass thermometer


10. Furnace up to 3000°C


11. Inexpensive method of measuring very
    small changes in temperature


12. Metal surface where a visual indication
    is required when the temperature reaches
    520 °C