Heat Transfer Mechanisms

It is the collective movement of molecules within fluids or gases. When a burner is placed at one side of a tumbler full of water, the different levels of heat can be felt in the tumbler. This explains convection. 

Heat is considered a form of energy because it represents the transfer of thermal energy between systems or objects due to temperature difference. It is not matter, mass, or fluid, but rather energy in transit that moves from hotter bodies to colder ones until thermal equilibrium is reached.

Heat always flows naturally from a region of higher temperature to a region of lower temperature due to the second law of thermodynamics. This spontaneous flow continues until thermal equilibrium is reached, meaning both objects attain the same temperature. Heat cannot flow from cold to hot without external work being done, such as in refrigeration systems.

A thermos flask (vacuum flask) prevents heat transfer through all three modes: conduction (by using a vacuum between walls), convection (vacuum eliminates air needed for convection currents), and radiation (silvered surfaces reflect infrared radiation). This comprehensive insulation makes it highly effective at maintaining temperature.

In solids, heat is transferred primarily through conduction - the process where heat energy is transferred through direct collision of neighboring particles within the material. Convection requires fluid movement (impossible in solids), and radiation is less significant in solid materials compared to conduction.

It is incorrect to say that heat cannot be transformed in other forms of energy. Heat energy is converted into mechanical energy. For example, a steam engine pulls a train.  

Energy is defined as the capacity to do work. The S.I unit of energy is Joule. When energy is transferred from one object to another due to temperature difference, it is called heat.

Photosynthesis is the process by which green plants prepare their own food. In this process, heat energy is trapped by chlorophyll for the conversion of raw material into carbohydrate.

The degree of hotness of a body is called its temperature. The direction of flow of heat energy is always from a body at higher temperature to a body at lower temperature. 

Statement (1) is correct. Infrared rays lie just under the visible light range in the electromagnetic spectrum. The molecules of IR rays are strike to oscillate, which produce heating effect. Statement (2) is wrong. For detecting forged bank notes, UV rays are used. Some bank notes have security elements either words or images printed onto the note using non-visible dyes, which fluorescence under ultraviolet light.

Non-shivering thermogenesis can be both obligatory and facultative. Obligatory thermogenesis is the heat production caused as a result of the metabolic rate, while facultative thermogenesis can be triggered in cold exposure to raise body temperature.

A layer of mud and straw is laid over the roof of the house in between the concrete and brick tiles. This layer does not conduct heat due to sun rays into the room of the house through the roof and helps to keep the room cool in summer.

Radiation heat transfer is concerned with the exchange of thermal radiation energy between two or more bodies. No medium is required for heat transfer by radiation; the radiation can travel through vacuum. For example, the heat is transferred from the sun to the earth by this method.

 Two thin blankets are warmer than a single blanket of same thickness as the two because some air sheet is enclosed in between them preventing heat flow .

Statement (1) is correct. Steam contains more heat than the same amount of water at the same temperature. When steam condenses, it gives out this extra latent heat and causes severe burns. Statement (2) is correct. The combination of low specific heat (requires less temperature to react) and high thermal conductivity (rapid transfer of heat) is the most desirable for a cooking pot.