Unit 7: Thermal Properties of Matter — Short Questions

Solids have fixed volume and shape because their particles are closely packed and have a fixed position in space, with strong forces holding them together.

Gases have neither fixed volume nor a fixed shape because:
i. Molecules are widely spaced.
ii. Molecules are free to move.
iii. Weak intermolecular forces.

In solids the particles are closely spaced due to strong interatomic forces but in case of liquids the spacing is greater than solids because of moderate intermolecular forces. The spacing in case of gases is much greater than solids and liquids due to weak forces.

Raising the temperature of a liquid increases the kinetic energy of its particles, causing them to move faster and spread out, eventually turning into vapours form.

The degree of hotness or coldness is called temperature of a body. It can also be defined as a physical quantity which determines the direction of flow of thermal energy.

Heat can be defined as "The energy that is transferred from one body to another due to a temperature difference between the two bodies."

A thermometric property in a physical property that changes with temperature some common thermometric properties include:
i. Volume expansion (e.g. Hg in a thermometer)
ii. Colour change (liquid crystal thermometer)
iii. Electrical resistance (e.g. thermistors)
iv. Pressure change (e.g. gas thermometer)

See answer from comprehensive Q.No.7.

Sensitivity of thermometer refers to how small change in temperature it can detect and measure.

Linearity of a thermometer refers to how directly its readings correspond to the actual temperature i.e. whether the temperature scale is evenly spaced and consistent.

The scale reading of a thermometer is accurate due to:
i. Calibration: The thermometer is calibrated against a known temperature standard.
ii. Linear expansion: The thermometric property (e.g., mercury expansion) changes linearly with temperature.
iii. Accurate markings: The temperature scale is accurately marked and evenly spaced.
iv. Proper construction: The thermometer is constructed to minimize errors and ensure consistent readings.

Temperature difference determines the direction of heat flow. Heat always flows from a body at a higher temperature to a body at a lower temperature.

Heat • Energy transferred between systems due to temperature difference.
• Can be gained or lost
• Measured in joules (J)

Internal Energy • Total energy of particles in a system
• Includes kinetic energy and potential energy of bonds
• Also measured in joules (J)

The heat flows from your hand to the cold surface because of fundamental nature of heat flow and laws of thermodynamics.

No, you can't feel fever by touching your own forehead. This is because your hand is at the same temperature as your forehead, so you won't be able to detect the heat.

(i) The walls of thermometer are made thin for:
• Reducing thermal mass.
• Increasing heat transfer
• Improving sensitivity.

(ii) The narrow inner bore in thermometer made to:
• Increase capillary action
• Improves sensitivity
• Reduces thermal lag

The pressure of a given mass of gas increases with temperature. So, pressure of a gas is also a thermometric property which is used in gas thermometers. The resistance of a given length of wire also depends upon temperature. It increases with the increase in temperature. So, the resistance of a wire is also a thermometric property

Thermometers use some property of a substance, which changes appreciably with the change of temperature are called thermometric properties.

The device which converts the heat energy into electrical energy is called thermistors.

The temperature of matter of which particles of stop their motion is called absolute zero temperature. Its value is 0K or −273.15°C.

According to this theory, matter is composed of very small particles called molecules which are always in motion. Their motion may be vibrational, rotational or linear. There exists a mutual force of attraction between the molecules know as intermolecular force. Tis force depends upon the distance between the molecules. It decreases with increasing distance between them.

The plasma is a gas in which most of the atoms are ionized containing positive ions and electrons. They are freely moving in the volume of the gas. Due to presence of positive ions and free electrons, plasma is the conduction state of matter. It allows electric current to pass through it.

Kinetic theory applies to plasma. It explains the random motion of ions and electrons, but additionally complexities like coulomb interaction and collective behavior also need to be considered.

Mercury is preferred to alcohol as a thermometric liquid because:
iii. High boiling point (357°C)
iv. Lower freezing point (−39°C) Mercury remains liquid at low temperature while alcohol solidifies at lower temperature.
v. Uniform expansion
vi. High density (Allows for more compact thermometer)
vii. Chemically stable does not wet the surface of glass tube.

Water is not suitable for use in thermometer because:
i. Freezing point: Water freezes at 0°C, making it unsuitable for measuring temperature below 0°C.
ii. Boiling water: Water boils at 100°C, limiting its range for measuring higher temperature.
iii. Expansion properties: Water expands when it freezes, which can cause the glass tube to burst. Expansion properties also make it less sensitive to temperature change.
iv. The equivalent temperature of 373 K on Celsius scale is 100°C and 212°F on Fahrenheit scale (without calculation).

Following are two ways to increase the sensitivity of a liquid-in-glass thermometer:
i. Narrow bore: By reducing the diameter of glas tube (bore), the thermometer becomes more sensitive. This is because a smaller bore requires less liquid expansion to register a temperature change, allowing for more precise measurement.
ii. Increasing liquid expansion co-efficient: Using a liquid with a higher expansion co-efficient (such as ethanol or pentane) instead of mercury or water, increases the sensitivity of thermometer. This is because liquids with higher expansion co-efficient expand more for a given temperature.

Specific heat capacity of water remains constant, the temperature rise will become half of original value, since the same amount of heat energy is spread over twice the mass of water. So, the temperature for 2 liters of water will approximately 1°C (half of the original 2°C rise).

There are no negative numbers on the Kelvins scale because it starts at absolute zero (0k), the lowest possible temperature where all molecular motion stops. Since temperature measures the thermal energy of a system, and energy cannot be less than zero, negative values are not possible on Kelvin scale.

A thermometer measures the temperature of substance not its own temperature. It measure the temperature of an external object or environment.

Metal objects feel colder than air temperature:
• Wooden objects feel closer to temperature.
• Cotton and plastic objects feel slightly warmer than air temperature.
This is because metals are good conductors of heat, quickly transferring heat away from your skin, making them feel colder. Wood and plastic are poorer conductors, while cotton is a poor conductor and a good insulator.

An increase in temperature of 1°C is greater than 1°F.
Reason: 1°C = 1.8°F

Gas molecules do not have same speed due to random motion and collisions, resulting in a distribution of speeds.

In an ideal vacuum, where no particles exist, temperature does not have any sense. However, in practical or at so physical contexts, we might refer to the effective temperature associated with radiations present in vacuum. Thus, it may make sense in specific contexts.

A hot body does not contain heat, instead, it has internal energy due to the motion of its particles. Heat only describes the energy transferred between systems due to a temperature difference.

The sun is matter because it is composed of physical substances (hydrogen, Helium, and other elements) in a plasma state, which have mass and occupy space. However, it also emits energy, which is not matter but a byproduct of the nuclear reaction taking place at sun.

See QNo.1.

See QNo.6.

See QNo.7.

See QNo.9.

The structure of glass in a thermometer is improved to enhance its sensitivity, range, and linearity. Here's how:

Sensitivity (i) Thin-walled glass: Using thin-walled glass reduces the thermal mass of the thermometer, allowing it to respond more quickly to temperature changes.
(ii) Uniform bore: A uniform bore (inner diameter) ensures that the mercury or alcohol column rises or falls uniformly, providing a more sensitive response to temperature changes.

Range (i) Long, narrow tube: A longer, narrower tube allows for a greater expansion and contraction of the mercury or alcohol column, increasing the thermometer's range.
(ii) Gradations: Careful gradations (markings) on the thermometer enable accurate readings over a wider temperature range.

Linearity (i) Constant internal diameter: Maintaining a constant internal diameter along the length of the thermometer ensures that the mercury or alcohol column expands and contracts linearly with temperature changes.
(ii) Accurate calibration: Accurate calibration of the thermometer ensures that the gradations are evenly spaced and correspond to a linear temperature scale.

By improving the structure of glass in a thermometer, manufacturers can create more sensitive, accurate, and reliable thermometers with a wider range and better linearity.