[theThinker (OP)]

I'll like to know if heat radiation may also involve radio wave frequencies. If a battery is connected to a resistor, does the radiation from the resistor also have frequencies in the radio wave ranges?     

[Colin2B]

For a pure resistor carrying dc no radio frequencies just emr at infrared frequencies.
However, if the circuit is carrying rf then it is possible for some electronic components to oscillate are those frequencies or harmonics and radiate a small amount of rf.

[chris]

A mains electricity cable produces radio waves doesn't it?

[jeffreyH]

A mains electricity cable produces radio waves doesn't it?

Good point. An antenna and alternating current are the prime example.

[Colin2B]

A mains electricity cable produces radio waves doesn't it?

Good point. An antenna and alternating current are the prime example.

Yes, the ac in the cable can produce elf radio but the cable needs to be long, one wavelength is about 6000km so 1/4 wave antenna would be more practical  Unless you can get this sort of length you will only get near field effect which is not the long distance emissions that we call radio waves.
The varying em field around an ac conductor is used in cable detectors as the field cuts through a coil in the detector, but again it is near field effect.

[jeffreyH]

A mains electricity cable produces radio waves doesn't it?

Good point. An antenna and alternating current are the prime example.

Yes, the ac in the cable can produce elf radio but the cable needs to be long, one wavelength is about 6000km so 1/4 wave antenna would be more practical  Unless you can get this sort of length you will only get near field effect which is not the long distance emissions that we call radio waves.
The varying em field around an ac conductor is used in cable detectors as the field cuts through a coil in the detector, but again it is near field effect.

Another good point.

[evan_au]

If a battery is connected to a resistor, does the radiation from the resistor also have frequencies in the radio wave ranges?

Every object above absolute zero radiates electromagnetic radiation, with a "black body" spectrum.

At the high-frequency end, the spectrum is limited by quantum effects, as each photon has a high energy.
At the low-frequency end, the spectrum does extend into the radio-frequency part of the spectrum. But because each photon has such low energy, the power in this part of the spectrum is pretty low.

There is a peak frequency which carries the bulk of the emitted power - at higher temperatures (such as when you put current through the element of an electric heater), this peak occurs at higher frequencies (changing from infra-red to visible red and then orange as you increase the power).
See: https://en.wikipedia.org/wiki/Black-body_radiation

But even at room temperature, there will be some radio-frequency photons emitted.

Studies of the Cosmic Microwave Background Radiation (CMBR) with an effective temperature of 2.7K find that the peak emission is at 160GHz, which is in the microwave part of the radio-frequency spectrum.

See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Features

[syhprum]

You beat me to it I had just produced a post saying the same thing

[theThinker (OP)]

If a battery is connected to a resistor, does the radiation from the resistor also have frequencies in the radio wave ranges?

Every object above absolute zero radiates electromagnetic radiation, with a "black body" spectrum.

At the high-frequency end, the spectrum is limited by quantum effects, as each photon has a high energy.
At the low-frequency end, the spectrum does extend into the radio-frequency part of the spectrum. But because each photon has such low energy, the power in this part of the spectrum is pretty low.

There is a peak frequency which carries the bulk of the emitted power - at higher temperatures (such as when you put current through the element of an electric heater), this peak occurs at higher frequencies (changing from infra-red to visible red and then orange as you increase the power).
See: https://en.wikipedia.org/wiki/Black-body_radiation

But even at room temperature, there will be some radio-frequency photons emitted.

Studies of the Cosmic Microwave Background Radiation (CMBR) with an effective temperature of 2.7K find that the peak emission is at 160GHz, which is in the microwave part of the radio-frequency spectrum.

See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Features

Thanks.

I think it is correct. From another forum, there was also mention about thermal noise 
in usual circuit elements -  meaning radio waves interference from normal thermal radiations.   

[Colin2B]

there was also mention about thermal noise 
in usual circuit elements -  meaning radio waves interference from normal thermal radiations.   

thermal noise isn't radio wave interference. It occurs in the conductor, but it is a problem in radio reception - particularly radio astronomy - where the received signal is of very low amplitude and the noise in the circuitry can overwhelm it.

When you said radio waves in your original question what did you mean? Usually it means those frequencies used for radio communication, but if you meant emr in general then heat = infra red is also emr.
Can I ask the reason for your question, are you getting radio frequency interference and wondering if a resistor is the source? If so, I would stress that a resistor is very unlikely to generate radio waves unless it is carrying radio frequency current.

[theThinker (OP)]

there was also mention about thermal noise 
in usual circuit elements -  meaning radio waves interference from normal thermal radiations.   

thermal noise isn't radio wave interference. It occurs in the conductor, but it is a problem in radio reception - particularly radio astronomy - where the received signal is of very low amplitude and the noise in the circuitry can overwhelm it.

When you said radio waves in your original question what did you mean? Usually it means those frequencies used for radio communication, but if you meant emr in general then heat = infra red is also emr.
Can I ask the reason for your question, are you getting radio frequency interference and wondering if a resistor is the source? If so, I would stress that a resistor is very unlikely to generate radio waves unless it is carrying radio frequency current.

My question is only a general one, whether a resistor with current radiates any radio wavelength (> 1 meter). I think the answer I get is yes; but the power is negligible.

[Colin2B]

whether a resistor with current radiates any radio wavelength (> 1 meter). I think the answer I get is yes; but the power is negligible.

In reality at say 10MHz it is less than a fraction of a percent/m² greater than that radiated by the circuit board it sits on (which is also negligible, if we assume a 20°C differential), however, the circuit board has a greater surface area so radiates a greater absolute level.