The variation in temperature occurs between the two systems, and heat can be transferred from the higher to the lower. The various heat transmission modes include:

• Conduction: The mechanism by which heat transfers from higher-temperature to lower-temperature entities. A higher area of kinetic energy converts thermal energy into a lower area of kinetic energy. High-speed particles collide with slow-speed particles, which increases their kinetic energy with slow-speed. Such heat transfer is a standard method and occurs by physical contact and is also called thermal conduction or heat conduction.

• Radiation: Radiation depicts the phenomenon of energy transfer through propagation, regardless of the medium, from one body to another. Electromagnetic radiation is a continuous source of energy for all bodies. Not only the body temperature but the surface properties also affect the speed of such an energy flow. When you sit before a campfire, the heat that meets you is mostly radiant energy.
• Convection: The thermal energy is transported whenever a substance such as air and fluid is heated and then moves from the spring; such phenomenon is called convection. The molecules expand at the molecular level as thermal energy is introduced. The fluid mass volume must rise by the same factor as the given fluid mass’s temperature rises. As hot air increases immediately, it drives in warmer, denser air. All such sequences of events illustrate the formation of convection currents.

• Ironing clothes is an example of conduction where heat is transmitted from iron to clothes.
• Heat is passed from the hands to the ice cube that causes an ice cube to melt as it is held upright.
• Boiling water, where denser molecules move at the bottom and the less compact molecules go upwards, leading to the molecules’ circular motion such that water is heated.
• An example of radiation is microwave radiation released from the oven.
• Another example of radiation is UV rays originating from the sun.
• Blood circulation occurs by the convection of warm-blooded animals and thereby controls the body temperature.

It is very pivotal to know the primary differences between boiling and evaporation. Evaporation is the transformation of moisture into vapour. Evaporation is a straightforward explanation of how water evaporates from the ground by light’s thermal action. On the other side, boiling is heating a liquid where the fluid temperature is higher than the material’s boiling point. The most significant major distinction between evaporation and boiling is that evaporation only occurs on the fluid’s surface when boiling happens over its vast mass.

Thermal expansion is a propensity for matter in response to a shift in temperature in shape, density and space. As the matter is heated, the kinetic energy of the molecules increases. The molecules then begin to vibrate and shift further and usually sustain a much more average separation. The low thermal expansion and the high thermal conductivity of a low-density material (without volume-producing improvements in the phase) are characteristics that improve its usage.

In contrast to volume, linear expansion means a transition in one dimension. The first estimate is linked to the shift in length dimensions in an object due to thermal expansion. The expansion means length shift or length rise. If the length transition over the volume occurs along a single dimension, the phenomenon is called linear expansion.

It happens due to the difference in temperature behind the expansion. It is, thus, implied that the temperature change reflects the expansion rate. Therefore, the concept of linear expansion explains how much substance can withstand whose original form and dimensions have changed due to heat radiation.

Volume expansion is known as the volume increase of the solids on heat, while surface expansion means the increase in the surface area of a solid on heating. Also, the surface expansion coefficient is defined as the ratio of increase in the area to its original area for each temperature increase.

The difference between solid and liquid expansion is linked to intermolecular forces that hold the substance together in the heating field. The constituent molecules for a solid substance are firmly connected due to intermolecular forces. It is also why solids have a specific form and length. If heated, these molecules absorb a certain amount of kinetic energy, start moving apart, and the expansion of materials is linear and volumetric.

Compared with a solid, the liquid’s molecules are not so intimately linked. These weakly bound molecules tend to move away from each other when heated. As the intermolecular forces are weaker, liquids expand faster than solids subjected to the same temperature rise.

The liquids and gases examples and real-world applications of expansion are as follows:

Liquids such as engine coolant or water follow a gradual discernible pattern of volume increase or decrease depending upon the subjected temperature. Unlike liquids, gases respond towards any temperature change at a greater rate due to their higher molecular kinetic energy. The application of volume expansion in gases can be witnessed in volume gas thermometers, where volume expansion is used to calibrate other thermometers.

Understanding heat transfer is essential for the development of heat energy systems. Coal-fired/gas-fired power plants are an example of these systems. Nuclear energy has been transformed into heat in nuclear power stations and produces steam to drive turbines.

1. Which method is used to transfer heat from the sun to the ocean?
   In case of interaction with water at a temperature varying from the ground, heat transfer is carried out by conduction.
   
   
2. What is the significance of heat transfer?
   The heat transfer method is used in various industrial processes, including extrusion, catalysis, gas processing, etc.
3. What is the basic difference between a positive heat transfer and a negative heat transfer?
   When the heat is transferred from a source to the system, the phenomenon is positive heat transfer, while the reciprocal is referred to as negative heat transfer.
4. How to compare expansivity in solids?
   To compare expansivity in solids, we need to establish the relationship between their heat energy, the volume and the movements of their entities.