The correct answer is D. All of the above.
Heat dissipation is the process of transferring heat from a hotter object to a cooler object. There are three main modes of heat dissipation: conduction, convection, and radiation.
Conduction is the transfer of heat between two objects that are in direct contact with each other. For example, when you touch a hot stove, the heat from the stove is transferred to your hand through conduction.
Convection is the transfer of heat through the movement of fluids. For example, when you boil water, the heat from the stove is transferred to the water through convection. The hot water rises to the top of the pot, while the cooler water sinks to the bottom. This creates a current that circulates the water and distributes the heat evenly.
Radiation is the transfer of heat through electromagnetic waves. For example, the sun radiates heat to the Earth through electromagnetic waves. This is why you can feel warm even when you are not in direct contact with the sun.
The heated parts of an electrical machine dissipate heat into their surroundings by all three modes of heat dissipation. Conduction occurs when the heat from the machine is transferred to the surrounding air and objects. Convection occurs when the heat from the machine causes the air to circulate, which carries the heat away from the machine. Radiation occurs when the heat from the machine is transferred to the surrounding air and objects through electromagnetic waves.
The amount of heat that is dissipated by each mode of heat dissipation depends on the specific design of the machine and the surrounding environment. For example, a machine that is in a well-ventilated area will dissipate heat more effectively through convection than a machine that is in a closed area.