Question

Thermal radiation is also called:
(A) Infrared radiation
(B) EM radiation
(C) Nuclear radiation
(D) None

Answer 1

Hint
To answer this question, we should know the wavelength ranges for each of the radiations as given in the options. If we compare different types of radiations and distinguish between them, then we will understand which of them is thermal radiation.

Complete step by step answer
When we analyse the electromagnetic spectrum, the wavelengths ranging from to are included in the thermal radiation. This range also includes a part of the ultraviolet region, visible and the whole infrared region.
Because of the word ‘thermal’, we may feel that the thermal radiation is just the infrared radiation. But it is not true. In the EM spectrum, the infrared region is roughly between to .
The electromagnetic radiation is the waves or quanta of waves produced due to the oscillating electric and magnetic fields. It includes the whole electromagnetic spectrum containing different type radiations such as radio waves, microwaves, infrared, visible, ultraviolet, x-rays and gamma rays.
When the photons or other particles are emitted due to the reactions involving nuclei of the atoms, the radiation is called nuclear radiation. This type of radiation comes under the ionizing part of the electromagnetic spectrum. The ionizing radiation such as X-rays and Gamma rays are examples of such nuclear radiation.
Therefore none of the first three options (Infrared radiation, electromagnetic radiation, and nuclear radiation) is the correct answer for this question.
So, the right answer is option (D).

Note
We may think that the thermal radiations are the infrared radiations, since the heat waves emitted from different bodies are in the form of infrared radiation. But thermal radiations also include visible light and ultraviolet also. For example, if we take an iron piece and try to heat it, we can see that on increasing the temperature, the colour emitted by the iron piece varies and it is in the visible range. So, all thermal radiations are not in the infrared regime.