21 Most VSAQ’s of Thermal Properties of Matter Chapter in Inter 1st Year Physics (TS/AP)

Table of Contents

2 Marks

VSAQ-1 : Why gaps are left between rails on a railway track?

Gaps are left between rails on a railway track primarily due to thermal expansion of the steel rails in response to temperature changes, especially during hot summer months. These gaps allow the rails to naturally expand without bending or buckling sideways, which could lead to potential train accidents, ensuring safe and reliable railway operations.

VSAQ-2 : State Newton’s law of cooling.

Newton’s Law of Cooling states that the rate of heat loss from an object is directly proportional to the temperature difference between the object (T(t)) and its surroundings (T_s). It can be mathematically expressed as:

$$\frac{{dT(t)}}{{dt}} = -k(T(t) – T_s)$$

Here,

T(t) represents the object’s temperature at a given time (Kelvin, K).
t represents time in seconds.
T_s is the temperature of the surrounding environment (Kelvin, K).
k is a cooling constant specific to the object (1/second).

In essence, this law describes how the temperature of an object changes over time as it loses heat to its cooler surroundings, with k determining the rate of cooling.

VSAQ-3 : What are the lower and upper fixing points in Celsius and Fahrenheit scales?

Celsius Scale:

Lower Fixed Point: The lower fixed point on the Celsius scale is defined as the freezing point of water at one atmosphere pressure, and it is set at 0°C.
Upper Fixed Point: The upper fixed point on the Celsius scale is defined as the boiling point of water at one atmosphere pressure, and it is set at 100°C.

Fahrenheit Scale:

Lower Fixed Point: The lower fixed point on the Fahrenheit scale is defined as the freezing point of water at one atmosphere pressure, and it is set at 32°F.
Upper Fixed Point: The upper fixed point on the Fahrenheit scale is defined as the boiling point of water at one atmosphere pressure, and it is set at 212°F.

VSAQ-4 : Can a substance contact on heating? Give an example.

Yes, certain substances can indeed contract on heating. An illustrative example is cast iron. When subjected to an increase in temperature, cast iron undergoes a phenomenon known as thermal contraction. This contraction occurs due to a reduction in the molecular vibrations within the material, leading to a decrease in its overall volume.

VSAQ-5 : Distinguish between heat and temperature.

Heat:

Nature: Heat is a form of energy transfer between objects due to temperature differences.
Measurement: It is measured in units such as joules (J) or calories (cal).
Effect: The addition or removal of heat can result in temperature changes or phase transitions in a substance.

Temperature:

Nature: Temperature is a measure of the average kinetic energy of particles within a substance.
Measurement: It is measured using scales like Kelvin (K) or Celsius (°C).
Effect: Changes in temperature indicate alterations in thermal energy content and drive the transfer of heat.

VSAQ-6 : What is greenhouse effect ? Explain global warming.

The greenhouse effect is a natural process where certain gases in Earth’s atmosphere, such as water vapor, carbon dioxide, and methane, trap incoming solar radiation from the Sun. These gases allow sunlight to pass through but absorb and re-radiate some of the heat energy emitted by the Earth, thereby warming the planet’s surface.

Global Warming:

Global warming is the gradual increase in Earth’s average surface temperature over time. It is primarily driven by human activities, such as burning fossil fuels and deforestation, which release additional greenhouse gases into the atmosphere. These extra greenhouse gases intensify the natural greenhouse effect, trapping more heat and leading to long-term temperature rise. This phenomenon has far-reaching environmental and climatic consequences.

VSAQ-7 : The roofs of buildings are often painted white during summer. Why?

During the summer, roofs are commonly painted white for two main reasons. Firstly, white surfaces have a unique property of reflecting a significant portion of sunlight and heat away from the building, thanks to their low absorptive power. This results in reduced heat absorption by the roof, which in turn helps in keeping the interior of the building cooler. Consequently, during hot weather, the occupants enjoy a more comfortable environment with a reduced indoor temperature, making white roofs an effective strategy for improving comfort and energy efficiency in buildings.

VSAQ-8 : Why are utensils coated black? why is the bottom of the utensils made of cooper?

Utensils are coated black primarily because black surfaces excel at absorbing and emitting heat. This property facilitates faster and more even cooking, as black utensils efficiently absorb and distribute heat.

VSAQ-9 : State the conditions under which Newton’s law of cooling is applicable.

Conditions for Applicability of Newton’s Law of Cooling:

The primary mode of cooling or heating of an object is through radiation.
The object is situated within a medium with forced convection, for instance, when there is airflow around the object.
The temperature of the object is uniformly distributed over its entire surface.
The temperature difference between the object and its surroundings remains moderate, typically up to 30 degrees Celsius.

VSAQ-10 : State Wein’s displacement law.

Wien’s displacement law asserts that the peak wavelength of the black-body radiation curve is inversely proportional to the temperature of the object. This implies that as the temperature of the object rises, the peak wavelength of the emitted radiation shifts towards shorter wavelengths (higher energy). This law is highly relevant for objects that emit thermal radiation, including stars and other hot entities, and it provides insights into the connection between an object’s temperature and the color of the emitted radiation.

VSAQ-11 : Ventilators are provided in rooms just below the roof. Why?

Ventilators are strategically placed in rooms just below the roof to ensure effective air circulation and ventilation. When the air within the room becomes hot, it naturally ascends through convection. The presence of ventilators enables this hot air to exit the room, initiating a continuous flow of air. Simultaneously, cooler air enters from below to replace the rising hot air. This process contributes significantly to maintaining a comfortable temperature inside the room, particularly in hot summers, and prevents the room from becoming stuffy or suffocating, thus promoting a more pleasant and breathable environment.

VSAQ-12 : Explain triple point of water.

The triple point of water is a unique state where water exists as a solid (ice), liquid (water), and gas (water vapor) simultaneously in equilibrium. It’s a crucial reference point for temperature measurement, occurring at 273.16 Kelvin, 0.01 degrees Celsius, or 32.018 degrees Fahrenheit, defining the Kelvin scale and ensuring accuracy in measurements.

VSAQ-13 : Why do liquids have no linear and a real expansions?

Liquids and gases, known as fluids, lack linear and areal expansions because they can flow and conform to their container’s shape. Unlike solids, which have a fixed shape, fluids do not possess specific length or area properties. Instead, their expansions are described by volume changes, such as thermal expansion for liquids and gases, and compressibility for gases, when subjected to temperature or pressure variations.

VSAQ-14 : What is latent heat of fusion?

The latent heat of fusion represents the quantity of heat energy needed to transform a substance from its solid state to its liquid state, all while maintaining a constant temperature and pressure, with no change in temperature. Throughout this transition, the substance absorbs heat energy to overcome the attractive forces among its particles, enabling them to transition from a fixed structure (solid) to a more fluid configuration (liquid). This parameter is unique to each substance and is quantified in units of joules per kilogram (J/kg) or calories per gram (cal/g).

VSAQ-15 : What is latent heat of Vaporization?

The latent heat of vaporization denotes the quantity of heat energy required to convert a unit mass of a liquid substance into its gaseous state at a constant temperature and pressure, without altering the temperature. During this transformation, the substance absorbs heat energy to break the intermolecular forces and transition from a dense liquid state to a more dispersed gaseous form. This property is unique to each substance and is quantified in units of joules per kilogram (J/kg) or calories per gram (cal/g). It plays a crucial role in various natural processes, including evaporation and boiling.

VSAQ-16 : What is triple point of water? Mention the values of temperature and pressure at triple point of water.

The triple point of water designates a specific combination of temperature and pressure at which water can coexist in all three of its states: solid (ice), liquid (water), and vapor (steam) in a state of equilibrium. In the case of water, this triple point occurs at a temperature of 273.16 Kelvin (0.01 degrees Celsius) and a pressure of 6.11 millibars (or approximately 6.11 x 10^-3 atmospheres or 610 pascals). At this unique point, the three phases harmoniously coexist, making it a pivotal reference for establishing the Kelvin scale, which is grounded in absolute temperature measurements.

VSAQ-17 : State Boyle’s law and Charles law.

Boyle’s Law: At a constant temperature, the volume (V) of a fixed amount of gas is inversely proportional to its pressure (P). In simple terms, when the pressure of a gas increases, its volume decreases, and vice versa, as long as the temperature remains constant.

Charles’s Law: At a constant pressure, the volume (V) of a given amount of gas is directly proportional to its absolute temperature (T). This means that as the temperature of a gas increases, its volume also increases, and conversely, when the temperature decreases, the volume decreases, provided the pressure remains constant.

VSAQ-18 : State the different modes of transmission of heat. Which of these modes require medium?

Heat can be transmitted through three primary modes:

Conduction: Heat transfer through direct contact within a material, no medium required.
Convection: Heat transfer through fluid movement (liquid or gas), medium needed.
Radiation: Heat transfer via electromagnetic waves, no medium needed; can occur in a vacuum.

VSAQ-19 : Is there any substance available in nature that contracts on heating? If so, give an example.

No, there are no naturally occurring substances that contract when heated. In general, most substances exhibit thermal expansion, where they expand when heated and contract when cooled. This behavior is a result of the increased kinetic energy of particles when heated, causing them to move more and occupy a larger volume (expansion). Conversely, cooling reduces particle energy, leading to a decrease in volume (contraction). Therefore, claims that certain substances like leather, rubber, or cast iron contract when heated are not accurate.

VSAQ-20 : What is thermal expansion?

Thermal expansion is the property of matter that describes its ability to change its shape, area, and volume in response to alterations in temperature. When a substance is heated, its particles absorb energy and become more mobile, resulting in the substance expanding. Conversely, when the substance is cooled, its particles lose energy, leading to a contraction. Thermal expansion plays a crucial role in various applications, including building construction and the operation of thermometers. It can be categorized into linear, areal, and volumetric expansion depending on the dimension of expansion or compression involved.

VSAQ-21 : Why is it easier to perform the skating on the snow?

Skating on snow is easier due to the phenomenon known as the pressure melting effect. When pressure is exerted on the snow beneath the skate blades, it causes the snow to slightly melt at the point of contact. This results in the formation of a thin layer of water between the skate and the snow surface, which effectively reduces friction. As a result, the skater experiences smoother gliding and reduced resistance, making it easier to execute skating maneuvers on the snow-covered surface.