Measurement of Temperature and Heat, Change of State and Latent Heat, Modes of Heat Transfer
Measurement of Temperature and Heat, Change of State and Latent Heat, Modes of Heat Transfer MCQ Questions
1.
What is the standard unit of temperature in the SI system?
Approach
The question asks for the standard unit of temperature in the International System of Units (SI). This requires knowledge of the fundamental SI units.
Step-by-step
- The International System of Units (SI) defines seven base units for seven fundamental physical quantities.
- One of these fundamental quantities is temperature.
- The SI base unit for thermodynamic temperature is the Kelvin.
- Other temperature scales like Celsius, Fahrenheit, and Rankine are also used, but they are not the standard SI unit.
Correct Option:
A) Kelvin is the standard unit of temperature in the SI system. It is an absolute temperature scale, meaning its zero point (0 K) is absolute zero, where all thermal motion ceases.
Incorrect Options
- B) Celsius is a widely used temperature scale, especially in many parts of the world for everyday measurements and in scientific contexts. However, it is a derived unit in the SI system, related to Kelvin by a simple offset (\(T_{\text{Celsius}} = T_{\text{Kelvin}} - 273.15\)). It is not the base SI unit.
- C) Fahrenheit is a temperature scale primarily used in the United States. It is not part of the SI system.
- D) Rankine is an absolute temperature scale, similar to Kelvin, but its degree size is equal to one degree Fahrenheit. It is not part of the SI system.
2.
What is the temperature at which water boils at standard atmospheric pressure?
D.
212 degrees Fahrenheit
ANSWER :
B. 100 degrees Celsius
Approach
The question asks for the boiling point of water at standard atmospheric pressure. This is a fundamental concept in physics and chemistry, and the answer depends on the temperature scale used. We need to identify the correct temperature in the given options.
Step-by-step
- Understand Boiling Point: The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure, allowing the liquid to turn into a gas (vaporize) throughout its bulk, not just at the surface.
- Standard Atmospheric Pressure: Standard atmospheric pressure is typically defined as 1 atmosphere (atm) or 101.325 kilopascals (kPa).
- Recall Water's Boiling Point: At standard atmospheric pressure, pure water boils at 100 degrees Celsius (\(100^\circ \text{C}\)).
- Convert to other scales (if necessary):
- To convert Celsius to Kelvin: \(K = ^\circ C + 273.15\). So, \(100^\circ \text{C} = 100 + 273.15 = 373.15 \text{ K}\).
- To convert Celsius to Fahrenheit: \(^\circ F = (^\circ C \times 9/5) + 32\). So, \(100^\circ \text{C} = (100 \times 9/5) + 32 = 180 + 32 = 212^\circ \text{F}\).
- Compare with options: We are looking for \(100^\circ \text{C}\), \(373.15 \text{ K}\), or \(212^\circ \text{F}\). Option B directly states \(100^\circ \text{C}\).
Correct Option:
B) 100 degrees Celsius. This is the internationally recognized boiling point of water at standard atmospheric pressure.
Incorrect Options
- A) 273 degrees Kelvin: This temperature is approximately \(0^\circ \text{C}\) (\(273.15 \text{ K}\)), which is the freezing point of water, not the boiling point.
- C) 0 degrees Celsius: This is the freezing point of water at standard atmospheric pressure, not the boiling point.
- D) 212 degrees Fahrenheit: While \(212^\circ \text{F}\) is indeed the boiling point of water, the question asks for "what is the temperature
3.
What is the freezing point of water in Celsius scale?
Approach
This question asks for the freezing point of water on the Celsius scale. This is a fundamental concept in physics and chemistry, and its value is a standard reference point for temperature measurement.
Step-by-step
- The Celsius scale is a temperature scale that defines the freezing point of water as 0 degrees and the boiling point of water as 100 degrees, both at standard atmospheric pressure.
- Therefore, by definition, the temperature at which water freezes is 0 °C.
Correct Option: A) 0 °C is the correct answer because the Celsius scale is defined such that 0 °C represents the freezing point of pure water at standard atmospheric pressure.
Incorrect Options
- B) 32 °C — This is the freezing point of water in the Fahrenheit scale, which is 32 °F. It is not 32 °C.
- C) -273.15 °C — This temperature represents absolute zero, the lowest possible temperature at which all molecular motion theoretically ceases. It is not the freezing point of water.
- D) 100 °C — This is the boiling point of water at standard atmospheric pressure on the Celsius scale, not its freezing point.
4.
What is the boiling point of water in Fahrenheit scale?
Approach
The question asks for the boiling point of water in the Fahrenheit scale. This is a fundamental concept in physics and general science, often tested in competitive exams. We need to recall the standard boiling point of water in Celsius and then convert it to Fahrenheit, or directly recall the Fahrenheit value.
Step-by-step
- Recall the boiling point in Celsius: The standard boiling point of water at sea level is \(100 \text{ °C}\).
- Recall the conversion formula: The formula to convert temperature from Celsius (\(C\)) to Fahrenheit (\(F\)) is given by:\[ F = C \times \frac{9}{5} + 32 \]
- Apply the formula: Substitute the boiling point of water in Celsius into the formula:\[ F = 100 \times \frac{9}{5} + 32 \]
- Calculate the Fahrenheit value:\[ F = 20 \times 9 + 32 \]\[ F = 180 + 32 \]\[ F = 212 \]So, the boiling point of water in Fahrenheit is \(212 \text{ °F}\).
Correct Option:
C) 212 °F is the correct boiling point of water on the Fahrenheit scale.
Incorrect Options
- A) -273.15 °F — This value is approximately absolute zero (\(-273.15 \text{ °C}\) or \(-459.67 \text{ °F}\)), which is the lowest possible temperature, not the boiling point of water.
- B) 0 °F — This is a specific point on the Fahrenheit scale, but it does not correspond to the freezing or boiling point of water. Water freezes at \(32 \text{ °F}\) and boils at \(212 \text{ °F}\).
- D) 100 °F — This is the boiling point of water in Celsius (\(100 \text{ °C}\)), not Fahrenheit. In Fahrenheit, \(100 \text{ °F}\) is a warm temperature, approximately \(37.8 \text{ °C}\), which is around body temperature.
5.
What is the temperature coefficient of resistance?
A.
The change in resistance per unit temperature change
B.
The change in temperature per unit resistance change
C.
The temperature at which resistance becomes zero
D.
The resistance at a specific temperature
ANSWER :
A. The change in resistance per unit temperature change
Approach
The question asks for the definition of the temperature coefficient of resistance. This is a fundamental concept in physics and electrical engineering, describing how the electrical resistance of a material changes with temperature. We need to recall its standard definition and mathematical representation.
Step-by-step
- Understand Resistance and Temperature: The electrical resistance of most materials changes with temperature. For conductors, resistance generally increases with temperature, while for semiconductors, it generally decreases.
- Define Temperature Coefficient of Resistance: The temperature coefficient of resistance, denoted by \(\alpha\), quantifies this change. It is defined as the fractional change in resistance per unit change in temperature.
- Mathematical Formulation: If \(R_0\) is the resistance at a reference temperature \(T_0\) (often \(0^\circ\text{C}\) or \(20^\circ\text{C}\)), and \(R_T\) is the resistance at temperature \(T\), then the change in resistance is \(\Delta R = R_T - R_0\) and the change in temperature is \(\Delta T = T - T_0\). The definition can be expressed as:
\[ \alpha = \frac{1}{R_0} \frac{\Delta R}{\Delta T} = \frac{1}{R_0} \frac{R_T - R_0}{T - T_0} \]From this formula, we can see that \(\alpha\) represents the change in resistance per unit original resistance per unit temperature change. Rearranging, \(\Delta R = \alpha R_0 \Delta T\). This implies that the change in resistance \(\Delta R\) is proportional to the original resistance, the temperature change, and the temperature coefficient. Therefore, the temperature coefficient itself describes the change in resistance per unit temperature change, normalized by the initial resistance.
More simply, it can be thought of as the change in resistance per unit temperature change, relative to the initial resistance. Option A captures the essence of this definition.
Correct Option:
A) The change in resistance per unit temperature change
This option correctly describes the essence of the temperature coefficient of resistance. While the precise definition includes a division by the initial resistance (fractional change), this option captures the primary physical meaning of how resistance varies with temperature.
Incorrect Options
B) The change in temperature per unit resistance change — This is the inverse of the concept and is not how the temperature coefficient of resistance is defined. The coefficient describes how resistance changes with temperature, not the other way around.
C) The temperature at which resistance becomes zero — This refers to a specific temperature, often related to superconductivity or the theoretical absolute zero for some materials, but it is not the definition of the temperature coefficient of resistance. The temperature coefficient describes the rate of change of resistance, not a specific point.
D) The resistance at a specific temperature — This describes a value of resistance at a particular temperature, e.g., \(R_T\) or \(R_0\). The temperature coefficient, however, describes how this resistance changes with temperature, not the value itself.
6.
What is the SI unit of temperature coefficient of resistance?
ANSWER :
D. Ohm per Kelvin
Approach
To determine the SI unit of the temperature coefficient of resistance, we need to recall its definition and the formula associated with it. The temperature coefficient of resistance describes how much the electrical resistance of a material changes for each degree of temperature change.
Step-by-step
- The resistance \(R_T\) of a material at a temperature \(T\) can be expressed in terms of its resistance \(R_0\) at a reference temperature \(T_0\) (often \(0^\circ \text{C}\) or \(20^\circ \text{C}\)) and its temperature coefficient of resistance \(\alpha\). The formula is given by:
\[ R_T = R_0 [1 + \alpha (T - T_0)] \]
- Rearranging the formula to isolate \(\alpha\):
\[ \alpha = \frac{R_T - R_0}{R_0 (T - T_0)} \]
- Now, let's analyze the units of each term in the formula for \(\alpha\):
- \(R_T - R_0\) is a difference in resistance, so its unit is Ohm (\(\Omega\)).
- \(R_0\) is resistance, so its unit is Ohm (\(\Omega\)).
- \(T - T_0\) is a difference in temperature. In SI units, temperature can be expressed in Kelvin (K) or Celsius (\(^\circ \text{C}\)). A change of \(1^\circ \text{C}\) is equal to a change of 1 K. So, the unit of \((T - T_0)\) is Kelvin (K).
- Substitute these units into the formula for \(\alpha\):
\[ \text{Unit of } \alpha = \frac{\Omega}{\Omega \cdot \text{K}} \]
- The Ohm units cancel out:
\[ \text{Unit of } \alpha = \frac{1}{\text{K}} = \text{K}^{-1} \]
- Therefore, the SI unit of the temperature coefficient of resistance is per Kelvin or Ohm per Kelvin (if we consider the change in resistance per unit resistance per unit temperature change, which is effectively the same).
Correct Option:
D) Ohm per Kelvin is the correct unit. While \(\text{K}^{-1}\) is the most precise SI unit, "Ohm per Kelvin" is also commonly used and implies the same physical quantity, as the resistance term in the numerator and denominator cancels out, leaving only the inverse of temperature.
Incorrect Options
- A) Ohm — Ohm is the SI unit of electrical resistance, not the temperature coefficient of resistance.
- B) Celsius — Celsius is a unit of temperature, not the temperature coefficient of resistance. Although temperature difference can be expressed in Celsius, the final unit is per degree of temperature.
- C) Kelvin — Kelvin is the SI unit of thermodynamic temperature, not the temperature coefficient of resistance.
