Temperature - Mechanical Engineering (MCQ) questions and answers

ANSWER: 300° C

Explanation:
The resistance and temperature relation is given by R = R₀ (1 + αt) by electric resistance thermometer.
where R₀ is the resistance at 0° C
R₀ = 2 ohm
R₁₀₀ =3 ohm
= (1 + α 100)
Therefore α = 0.005
Now,
R= 5 ohm
5 = 2 (1 + 0.005t)
t = 300° C

ANSWER: Seebeck effect

Explanation:
The Seebeck effect states that when two ends of a thermocouple are kept at different temperatures then the emf is generated in the circuit depending on the temperature difference between the hot and the cold junction. Therefore emf is a thermometric property of the circuit. The thermocouple is calibrated by measuring the thermal emf at various known temperatures, the reference junction being kept at 0° C. Peltier effect is exact opposite of Seebeck effect that the temperature difference is created by applying the voltage between two junctions of thermocouple circuit.

ANSWER: resistance of a metal wire

Explanation:
When current passes through a metal wire, as the temperature increases the resistance increases due to vibration of molecules in metal and collision of electrons carrying current. Therefore resistance of a metal wire is taken as a thermometric property in electric resistance thermometer. A suitable wire may be used for measuring temperature and the setup is arranged in a Wheatstone bridge circuit. Usually platinum wire is used as it can measure temperature to a high degree of accuracy and sensitivity. Platinum makes electric resistance thermometer suitable for the calibration of other thermometers.

ANSWER: P V = m R T

Explanation:
The pressure–volume –temperature relation of any gas at low pressure is given by,
p v = R T
where R is the universal gas constant and is the molar specific volume, m³/gmol. Dividing it by the molecular weight μ,
p v = R T
where v is the specific volume in, m³/kg and R is the characteristic gas constant.
In terms of total volume of gas we can wright this equation as,
P V = n R T
P V = m R T
Where n is the number of moles and m is mass of gas. This equation is called as ideal gas equation of state.

ANSWER: Gas

Explanation:
When the temperature of a system is measured simultaneously with all the above thermometers which are in options, then it is found that there are considerable variations among the readings. But with experiments, it is found that the minimum variation is observed among the gas thermometers. Therefore gas is chosen as a standard thermometric substance.

ANSWER: Thermometric property

Explanation:
Thermal equilibrium is achieved by heat transfer between two bodies which are at different temperature. To obtain a quantitative measure of the temperature of any body, a reference body is used and a particular physical characteristic of that reference body is selected which changes with temperature. The change in the selected characteristic is the indication as change in temperature. This selected characteristic is called as thermometric property, and the reference body is called as thermometer. Mercury is a common example of the thermometer.

ANSWER: Zeroth law of thermodynamics

Explanation:
When a body A is in thermal equilibrium with a body B, And also the same body A is in thermal equilibrium with a body C, then body B and body C are also in thermal equilibrium with each other. This is called as Zeroth Law of Thermodynamics. It is the basis of temperature measurement.

ANSWER: Temperature

Explanation:
Temperature plays a very important role in thermodynamics as force does in static and velocity does in dynamics. Temperature is the term through which we can differentiate between hot and cold. When two bodies are brought in physical contact with each other and one body has more temperature than other then hear transfer takes place from hot body to cold one. After some time they attain a common temperature and then they are in a thermal equilibrium. These phenomena are very important in thermodynamics.