Advertisements
Advertisements
Question
The constants a and b for the pair silver-lead are 2.50 μV°C−1 and 0.012μV°C−2, respectively. For a silver-lead thermocouple with colder junction at 0°C, ______________ .
(a) there will be no neutral temperature
(b) there will be no inversion temperature
(c) there will not be any thermo-emf even if the junctions are kept at different temperatures
(d) there will be no current in the thermocouple even if the junctions are kept at different temperatures
Advertisements
Solution
(a) there will be no neutral temperature
(b) there will be no inversion temperature
The temperature of the hot junction at which the thermo-emf in the thermocouple becomes maximum is called neutral temperature for that thermocouple. The signs of the constants a and b are same. Therefore from the relation, \[\theta_n = - \frac{a}{b},\] the neutral temperature will be less than the temperature of the cold junction of thermocouple.
Hence, there will be no neutral or inversion temperature, as the temperature of the hot junction cannot be less than the temperature of the cold junction.
APPEARS IN
RELATED QUESTIONS
A silver wire has a resistance of 2.1 Ω at 27.5°C, and a resistance of 2.7 Ω at 100°C. Determine the temperature coefficient of resistivity of silver.
A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0°C? The temperature coefficient of resistance of nichrome averaged over the temperature range involved is 1.70 × 10−4 °C−1.
The order of coloured rings in a carbon resistor is red, yellow, blue and silver. The resistance of the
carbon resistor is:
a) 24 x 106 Ω ± 5%
b) 24 x 106 Ω ± 10%
c) 34 x 104 Ω ± 10%
d) 26 x 104 Ω ± 5%
Draw labelled graphs to show how electrical resistance varies with temperature for:
1) a metallic wire.
2) a piece of carbon
Is work done by a battery always equal to the thermal energy developed in electrical circuit? What happens if a capacitor is connected in the circuit?
A non-ideal battery is connected to a resistor. Is work done by the battery equal to the thermal energy developed in the resistor? Will your answer change if the battery is ideal?
Sometimes it is said that "heat is developed" in a resistance when there is an electric current in it. Recall that heat is defined as the energy being transferred due to temperature difference. Is the statement in quotes technically correct?
The resistance of an iron wire and a copper wire at 20°C are 3.9 Ω and 4.1 Ω, respectively. At what temperature will the resistance be equal? Temperature coefficient of resistivity for iron is 5.0 × 10–3 K–1 and for copper, it is 4.0 × 10–3 K–1. Neglect any thermal expansion.
When a current passes through a resistor, its temperature increases. Is it an adiabatic process?
Consider the following statements regarding a thermocouple.
(A) The neutral temperature does not depend on the temperature of the cold junction.
(B) The inversion temperature does not depend on the temperature of the cold junction.
An electric kettle used to prepare tea, takes 2 minutes to boil 4 cups of water (1 cup contains 200 cc of water) if the room temperature is 25°C. (a) If the cost of power consumption is Re 1.00 per unit (1 unit = 1000 watt-hour), calculate the cost of boiling 4 cups of water. (b) What will be the corresponding cost if the room temperature drops to 5°C?
Find the thermo-emf developed in a copper-silver thermocouple when the junctions are kept at 0°C and 40°C. Use the data given in the following table.
| Metal with lead (Pb) |
a `mu V"/"^oC` |
b `muV"/("^oC)` |
| Aluminium | -0.47 | 0.003 |
| Bismuth | -43.7 | -0.47 |
| Copper | 2.76 | 0.012 |
| Gold | 2.90 | 0.0093 |
| Iron | 16.6 | -0.030 |
| Nickel | 19.1 | -0.030 |
| Platinum | -1.79 | -0.035 |
| Silver | 2.50 | 0.012 |
| Steel | 10.8 | -0.016 |
Find the neutral temperature and inversion temperature of a copper-iron thermocouple if the reference junction is kept at 0°C. Use the data given in the following table.
| Metal with lead (Pb) |
a `mu V"/"^oC` |
b `muV"/("^oC)` |
| Aluminium | -0.47 | 0.003 |
| Bismuth | -43.7 | -0.47 |
| Copper | 2.76 | 0.012 |
| Gold | 2.90 | 0.0093 |
| Iron | 16.6 | -0.030 |
| Nickel | 19.1 | -0.030 |
| Platinum | -1.79 | -0.035 |
| Silver | 2.50 | 0.012 |
| Steel | 10.8 | -0.016 |
By increasing the temperature, the specific resistance of a conductor and a semiconductor -
The higher and lower fixed points on a thermometer are separated by 160 mm. When the length of the mercury thread above the lower point is 40 mm, the temperature reading would be :
