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Effects of heat Questions

Chapter: Heat and Its Transmission | Total Available: 10 Real Questions

Question 1 of 10 Authentic UPSC NDA Question

 Evaporation from the surface of a given liquid takes place more rapidly when

Step-by-Step Logic & Solution

Correct Answer

✓ Option A is correct. Evaporation occurs more rapidly at higher temperatures and larger surface areas.

📖 Governing Law / Core Concept

Evaporation is governed by the principles of thermodynamics, specifically, the rate of change of phase between liquid and gas states, which is influenced by factors like temperature and surface area.

🧪 Step-by-Step Breakdown

Evaporation involves molecules at the surface of a liquid gaining enough energy to escape into the gas phase. Key factors influencing this process include:

  • Temperature: Higher temperatures increase kinetic energy, allowing more molecules to overcome intermolecular forces.
  • Surface Area: More surface area exposes more molecules to the air, enhancing evaporation.

Therefore, the rate of evaporation can be expressed as:

\[ Rate \propto A \cdot e^{-\frac{E}{kT}} \]

where:

  • Rate: The amount of liquid evaporated per unit time.
  • A: Surface area of the liquid.
  • E: Activation energy for the phase change.
  • k: Boltzmann's constant.
  • T: Absolute temperature (Kelvin).

🔍 Option Analysis

  • Option B: Low temperature reduces kinetic energy, decreasing evaporation.
  • Option C: Low temperature and small surface area hinder evaporation.
  • Option D: Higher temperature benefits evaporation; small surface area does not.

⚡ Mnemonic / Speed-Run

Remember: High temperature + Large area = Rapid evaporation (H + A = R).

6. Visual Suggestion

6. Visual Suggestion

A schematic diagram illustrating increasing evaporation with large surface area and high temperature, perhaps with arrows indicating increased molecular energy on the surface.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Physics, Chapter 12 (Thermodynamics).

Question 2 of 10 Authentic UPSC NDA Question

Water is heated with a coil of resistance R connected to domestic supply. The rise of temperature of water will depend on

(1) Supply voltage.

(2) Current passing through the coil.

(3) Time for which voltage is supplied. Select the correct answer from among the following : 

Step-by-Step Logic & Solution

Correct Answer

✓ Option (a) is correct. The temperature rise depends on all three factors: supply voltage, current through the coil, and time.

📖 Governing Law / Core Concept

The temperature rise in water due to the heating coil can be described by the formula:

\[ Q = V \cdot I \cdot t \text{, where } Q \text{ is heat energy (in J), } V \text{ is voltage (in V), } I \text{ is current (in A), and } t \text{ is time (in s).} \]

The heat energy transferred to the water leads to a temperature increase.

🧪 Step-by-Step Breakdown

The total heat energy supplied is given by:

\[ Q = m \cdot c \cdot \Delta T \text{ (where } m \text{ is mass of water, } c \text{ is specific heat capacity, and } \Delta T \text{ is temperature rise).} \]

From Ohm's Law, we have:

\[ V = I \cdot R \]

Substituting for \(I\) gives:

\[ Q = (V/R) \cdot V \cdot t = \frac{V^2 \cdot t}{R} \]

This shows temperature increase depends on voltage \(V\), current \(I\), and time \(t\).

🔍 Option Analysis

Option (b): Incorrect, only mentions voltage and current but omits time.

Option (c): Incorrect, only addresses voltage.

Option (d): Incorrect, combines only current and time but ignores voltage.

⚡ Mnemonic / Speed-Run

Remember: "VIT" = Voltage, Current, Time - all are crucial for heating water!

📊 Visual Suggestion

📊 Visual Suggestion

A flowchart displaying the relationship between heat energy (Q), voltage (V), current (I), resistance (R), and time (t) in heating processes. Include an illustration of a heating coil in a container of water to visually represent energy transfer.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Physics, Chapter 12 (Thermodynamics).

Question 3 of 10 Authentic UPSC NDA Question

10 g of ice at -10 °C is is mixed with 10 g of water at 0 °C. The amount of heat required to raise the temperature of mixture to 10 °C is

Step-by-Step Logic & Solution

Solution

Option (c) is correct.

Explanation:

\[ Q = m \cdot c \cdot \Delta T \]
\[ Q_{ice} = m_{ice} \cdot c_{ice} \cdot (0 - (-10)) + m_{ice} \cdot L_f + m_{water} \cdot c_{water} \cdot (10 - 0) \]
\[ Q_{ice} = 10 \cdot 0.5 \cdot (10) + 10 \cdot 80 + 10 \cdot 1 \cdot (10) \]
\[ = 50 + 800 + 100 \]
\[ = 950 \text{ cal} \]
\[ Q_{total} = Q_{ice} + Q_{water} \]
\[ Q_{total} = 950 + 100 = 1050 \text{ cal} \]
📌 Hints / Properties Used:
  • Specific heat of ice: \(c_{ice} = 0.5 \text{ cal/g°C}\)
  • Latent heat of fusion: \(L_f = 80 \text{ cal/g}\)
  • Specific heat of water: \(c_{water} = 1 \text{ cal/g°C}\)
📊 Visual Diagram Suggestion:

A schematic showing the phase change of ice to water, including temperature changes, highlighting energy transfer at each step from ice at -10°C to ice at 0°C, water heating from 0°C to 10°C, and heat values involved.

📖 Factual Verification & Reference:

Verified against NCERT Class XII Physics, Chapter 11 (Thermodynamics).

Question 4 of 10 Authentic UPSC NDA Question

The temperature at which “vapour pressure of the liquid in an open vessel becomes equal tothe atmospheric pressure” is called

Step-by-Step Logic & Solution

Correct Answer

✓ Option B is correct. The boiling point is the temperature at which the vapor pressure of a liquid equals atmospheric pressure.

📖 Governing Law / Core Concept

The temperature at which the vapor pressure of a liquid equals the atmospheric pressure is defined as the boiling point.

🧪 Step-by-Step Breakdown

At boiling point:

\[ P_{vapor} = P_{atmospheric} \]

Where:

  • Pvapor = Vapor pressure of the liquid (measured in pascals, Pa)
  • Patmospheric = Atmospheric pressure (assumed standard value = 101.3 kPa)

When \( P_{vapor} \) reaches \( P_{atmospheric} \), bubbles of vapor form within the liquid, resulting in boiling.

🔍 Option Analysis

  • A: Melting point - The temperature at which a solid becomes a liquid.
  • C: Liquid point - Not a standard term in thermodynamics.
  • D: None of the above - This is incorrect as option B accurately identifies the boiling point.

⚡ Mnemonic / Speed-Run

To remember boiling point concepts: "Bubbles Boil at Boiling Point".

6. Visual Suggestion

6. Visual Suggestion

A diagram illustrating a boiling liquid in a pot, showing temperature arrows, vapor pressure, and atmospheric pressure lines, helping visualize how boiling occurs when vapor pressure equals atmospheric pressure.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 11 Physics, Chapter 1 (Thermodynamics).

Question 5 of 10 Authentic UPSC NDA Question

A system that does NOT allow exchange of heat with its surrounding is called

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option A is correct. A system that does not allow the exchange of heat with its surroundings is called an adiabatic system.

📖 Core Concept

An adiabatic system isolates itself thermally from its environment, meaning that no heat is transferred in or out, thus enabling internal energy changes from work done directly.

💡 3. Explanation

An adiabatic process is defined as one where the heat transfer (\(Q\)) equals zero. Therefore:
\[ Q = 0 \]
It follows that any work done on or by the system alters its internal energy without heat exchange with the environment. The first law of thermodynamics expresses this as:
\[ \Delta U = W \]
Thus, for an adiabatic system: - If the system does work on the surroundings, it loses internal energy. - If work is done on the system, it gains internal energy, effectively illustrating the principles of energy conservation in thermodynamic processes.

❌ 4. Option Analysis

  • •Option B: A non-adiabatic system allows heat exchange with its surroundings, which contradicts the definition of an adiabatic system.
  • •Option C: An equilibrium system describes a state where all processes occur at equal rates, and does not specifically entail heat exchange characteristics.
  • •Option D: A non-equilibrium system is characterized by ongoing changes, and it does not directly correlate with heat exchange properties like those defined in adiabatic systems.
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember the mnemonic "Adi-bag" where "Adi" stands for Adiabatic, indicating a closed system with no heat exchange.

🎯

5. Key Takeaways

An adiabatic system describes a process with no heat exchange, focusing purely on work-related changes in internal energy.

Question 6 of 10 Authentic UPSC NDA Question

Given below are the four cases in which certainheat transfer is taking place:

1. Ice is melting in a glass full of water.

2. Water is boiling in an open container.

3. A metal rod is heated in a furnace.

4. A cup of coffee is allowed to cool on a table.

In which of the above cases can Newton’s law of cooling be applied?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (b) is correct. Newton's law of cooling applies primarily in case 4.

📖 Governing Law / Core Concept

Newton's Law of Cooling states:

\[ \frac{dT}{dt} = -k(T - T_{env}) \]

Where \( T \) is the temperature of the object, \( T_{env} \) is the ambient temperature, and \( k \) is the cooling constant.

🧪 Step-by-Step Breakdown

Analyzing the cases:

  • Case 1: Ice melting involves latent heat transfer, not applicable under cooling laws.
  • Case 2: Water boiling signifies a phase change, rendering Newton's law irrelevant.
  • Case 3: Heating a metal rod increases temperature; different laws for heat transfer apply.
  • Case 4: A cup of coffee cooling aligns with Newton's law as it approaches \( T_{env} \).

🔍 Option Analysis

  • Option A: Incorrect; ice melting does not signify cooling.
  • Option C: Incorrect; case 1 is not applicable.
  • Option D: Incorrect; boiling water doesn't relate to cooling dynamics.

⚡ Mnemonic / Speed-Run

Recall cooling occurs when: 1) the object is warmer than its environment, and 2) the cooling rate is proportional to the temperature difference.

6. Visual Suggestion

Illustrate Newton's Law of Cooling with a graph showing the temperature decrease of a cooling cup of coffee over time as it approaches ambient temperature.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Physics, Chapter on Thermodynamics and Heat Transfer.

Question 7 of 10 Authentic UPSC NDA Question

Which one of the following statements best defines the concept of heat?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. Heat is defined as the transfer of energy due to a temperature difference.

📖 Governing Law / Core Concept

Heat transfer is governed by the Second Law of Thermodynamics, which states that energy flows spontaneously from regions of higher temperature to lower temperature until thermal equilibrium is achieved.

🧪 Step-by-Step Breakdown

Heat (\( Q \)) is quantitatively expressed by the formula:

\[ Q = mc\Delta T \]

Where:

  • m = mass of the substance (kg)
  • c = specific heat capacity (J/kg·°C)
  • \(\Delta T\) = change in temperature (°C)

This formula underscores that heat represents the transfer of energy across a temperature gradient.

🔍 Option Analysis

  • A: Incorrect. Describes energy transformation but not heat transfer specifically.
  • B: Incorrect. Refers to mass-energy equivalence, not heat transfer.
  • D: Incorrect. Relates to thermal expansion, not the concept of heat.

⚡ Mnemonic / Speed-Run

Recall: "Hot to Cold" - Heat moves from areas of high temperature to low temperature.

6. Visual Suggestion

A diagram illustrating a hot object transferring heat to a cold object, visually representing the direction of energy flow and the temperature difference.

📖 Factual Verification & Reference:

Verified against NCERT Class XI Physics, Chapter 14 (Heat).

Question 8 of 10 Authentic UPSC NDA Question

Consider the two statements given below:

Statement 1: Infrared waves are also called heat waves.

Statement 2: Water molecules readily absorb infrared waves.

Select the correct answer using the code given below:

Step-by-Step Logic & Solution

Correct Answer

✓ Option B is correct. Both statements are true, but Statement 2 does not explain Statement 1.

📖 Governing Law / Core Concept

Infrared waves, commonly known as heat waves, belong to the electromagnetic spectrum and are responsible for thermal radiation. Water molecules absorb infrared radiation leading to an increase in their thermal energy.

🧪 Step-by-Step Breakdown

Statement 1: Infrared waves raise the temperature of objects they contact, thus referred to as heat waves.

Statement 2: Water's high absorption capacity for infrared radiation is due to its molecular structure, leading to increased kinetic motion of the molecules.

Since both statements are scientifically accurate but do not directly correlate, we conclude that:

\[ \text{Statement 1: True} \]
\[ \text{Statement 2: True, but not an explanation} \]

🔍 Option Analysis

Option A states both are true and 2 explains 1, which is incorrect.

Option C claims 1 is true and 2 is false, which is incorrect.

Option D asserts 2 is true and 1 is false, which is incorrect.

⚡ Mnemonic / Speed-Run

Remember: "Infrared = Heat + Absorption" to assert that while they are interconnected, one does not explain the other causally.

6. Visual Suggestion

6. Visual Suggestion

Include a diagram illustrating the electromagnetic spectrum highlighting infrared waves and a water molecule's absorption mechanism showing increased thermal motion.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Physics, Chapter 15 (Waves and Sound).

Question 9 of 10 Authentic UPSC NDA Question

A liquid is heated up to a certain temperature. Which one of the following situation would correspond to the boiling of the liquid?

Step-by-Step Logic & Solution

Explanation: At boiling point vapour pressure become equal to atmospheric pressure.

Question 10 of 10 Authentic UPSC NDA Question

Radiations coming from the Sun are mostly in the form of

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. The Sun emits both visible light and short-wavelength infrared radiation.

📖 Governing Law / Core Concept

The electromagnetic spectrum describes the range of all possible frequencies of electromagnetic radiation, where visible light and infrared occupy a significant portion.

🧪 Step-by-Step Breakdown

Radiation from the Sun primarily consists of:

  • Visible Light: The light we can see.
  • Short-Wavelength Infrared: This includes infrared radiation just beyond the visible spectrum.

Most solar radiation reaches Earth in the form of:

\[ \text{Total Solar Radiation} \approx \text{Visible Light} + \text{Short-Wavelength Infrared} \]

🔍 Option Analysis

  • Option (a): Incorrect, as it excludes infrared.
  • Option (b): Incorrect, as it mentions long-wavelength infrared, which is not predominant.
  • Option (d): Incorrect, as it includes both types of infrared; only short-wavelength is primarily emitted.

⚡ Mnemonic / Speed-Run

Remember: "Visible shines, infrared aligns."

6. Visual Suggestion

6. Visual Suggestion

A diagram illustrating the electromagnetic spectrum, highlighting the visible light and short-wavelength infrared sections, would aid understanding.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Physics, Chapter on Electromagnetic Waves.

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