No, electromagnetic waves from thermal radiation, also known as thermal radiation or blackbody radiation, are not pure sinusoids.
Thermal radiation is emitted by objects due to their temperature, and it consists of a continuous spectrum of electromagnetic waves covering a range of frequencies. This spectrum is known as the Planck spectrum or blackbody spectrum. According to Planck's law, the intensity of radiation emitted by a blackbody is a function of both frequency and temperature.
The shape of the blackbody spectrum depends on the temperature of the object. At low temperatures, the spectrum is dominated by longer-wavelength radiation in the infrared region. As the temperature increases, the spectrum shifts towards shorter wavelengths, encompassing the visible, ultraviolet, and even X-ray and gamma-ray regions at extremely high temperatures.
The blackbody spectrum does not exhibit a simple sinusoidal pattern because it is not a single-frequency wave. Instead, it represents the combination of many different frequencies, each contributing to the overall intensity of the thermal radiation. The distribution of these frequencies follows the shape of the blackbody spectrum, which is typically described by Planck's law or the Stefan-Boltzmann law.
In summary, thermal radiation consists of a broad spectrum of electromagnetic waves with various frequencies, and it does not exhibit a pure sinusoidal waveform.