Question

Thermal radiation are:
A. Electromagnetic wave
B. Mechanical transverse wave
C. Mechanical longitudinal wave
D. None of the above

Answer 1

Hint-The heat emitted due to the energy transition of atoms, molecules or electrons of a substance is called thermal radiation. Temperature is a measure of thermal radiation. If temperature increases then the rate of thermal radiation also increases.
Energy transfer in thermal radiation is by electromagnetic waves. All objects can emit thermal radiation. The hotter an object thermal radiation emitted will be more. The radiations emitted by hot objects will be at shorter wavelength which means at high energy. Whereas, cold objects will emit most of the radiations at longer wavelengths that are at a lower energy.

Step by step solution:

The heat emitted due to the energy transition of atoms, molecules or electrons of a substance is called thermal radiation. Temperature is a measure of thermal radiation. If temperature increases then the rate of thermal radiation also increases.

Energy transfer in thermal radiation is by electromagnetic waves. All objects can emit thermal radiation. The hotter an object, thermal radiation emitted will be more. The radiations emitted by hot objects will be at shorter wavelength which means at high energy. Whereas, cold objects will emit most of the radiations at longer wavelengths that are at a lower energy.

Thermal radiation takes place when the atoms are heated up so that kinetic energy is released resulting in the vibration of the atoms. The energy that atoms accumulate through vibration is constantly released as electromagnetic radiation.
Examples of thermal radiations are the heating of earth by the sun, heating of room by an open hearth, fireplace etc. The flames, Coals and hot bricks radiate heat to the objects in the room.

The range of thermal radiation is from long infrared through visible light to the short ultraviolet rays. The black body radiation is also thermal radiation. Intensity of distribution of radiant energy will be governed by the temperature of the surface that is emitting the radiation.

Note: Since, thermal radiations are in the form of electromagnetic radiation emitted by the heated surface in all directions, they travel at the speed of light directly to the point of absorption. The electromagnetic radiation does not require an intervening medium to travel. So, thermal radiations can travel through vacuum.